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Papers by Marcel Egger

Uptake-leak balance of SR Ca2+ determines arrhythmogenic potential of RyR2R420Q+/− cardiomyocytes

Journal of Molecular and Cellular Cardiology

Journal of Molecular and Cellular Cardiology, 2020

Impairment of vascular responsiveness to nitric-oxide (NO•), or NO-resistance, occurs in many car... more Impairment of vascular responsiveness to nitric-oxide (NO•), or NO-resistance, occurs in many cardiovascular diseases. It is prominent especially in poorly-controlled diabetic individuals. We investigated HNO donor, isopropylamine NONOate (IPA-NO), offers haemodynamic advantages over the NO• donor, diethylamine NONOate (DEA-NO), in diabetic myocardium. After 8-weeks of streptozotocin diabetes (55 mg/kg i.v.) or citrate-vehicle sham (n = 12-16/group), hearts were isolated from anesthetized adult male rats (ketamine-xylazine 100-12 mg/kg, i.p.) and Langendorff-perfused. Following U46619 pre-constriction of the coronary vasculature to 50% of basal flow, dose-response curves to acute bolus doses of IPA-NO or DEA-NO (10 pmol-10 μmol) were performed. Blood glucose levels (31 ± 2 mM) were markedly elevated, body weight (291 ± 5 g) was significantly lower, in diabetic rats compared to sham (blood glucose 9 ± 1 mM, body weight 460 ± 5 g). Diabetes impaired NO•-induced LV-maximal relaxation by 50% (↓LV-dP/dt 150 ± 8 mmHg/s), LV-maximal contractile function by 22% (↑LV + dP/dt 322 ± 14 mmHg/s) and maximal coronary vasodilatation by 32% (↑4.2 ± 0.2 ml/min), compared to non-diabetic counterparts (↓LV-dP/dt 300 ± 10 mmHg/s, ↑LV + dP/dt 410 ± 10 mmHg/s, coronary-flow ↑5.8 ± 0.52 ml/min, p b .05). In contrast, HNO enhanced LV-maximum relaxation by 40% (↓LV-dP/dt 280 ± 10 mmHg/s) and LV-contractile function by 120% (↑LV + dP/dt 260 ± 20 mmHg/s), with preserved vasodilation (↑4.1 ± 0.1 ml/min) in diabetic myocardium, compared to non-diabetic counterparts (↓LV-dP/dt 200 ± 13 mmHg/s, ↑LV + dP/dt 120 ± 15 mmHg/s, coronary-flow ↑4.0 ± 0.2 ml/min, p b .05). These results provide the first evidence that NOresistance occurs in diabetic myocardium, and HNO largely circumvents this phenomena. These results support potential roles for therapeutic HNO administration in acute treatment of heart disease in diabetes.

Poster: Automatic detection, characterization, and classification of local Ca2+ release events in... more Poster: Automatic detection, characterization, and classification of local Ca2+ release events in cardiomyocytes

Ca2+ waves and the arrhythmogenicity paradigm: role of SERCA stimulation in a CPVT mouse model

Biophysical Journal, 2022

Bulletin des Médecins Suisses, 2022

Cardiac hypertrophy is associated with alterations in cardiomyocyte excitation-contraction coupli... more Cardiac hypertrophy is associated with alterations in cardiomyocyte excitation-contraction coupling (ECC) and Ca 2ϩ handling. Chronic elevation of plasma angiotensin II (Ang II) is a major determinant in the pathogenesis of cardiac hypertrophy and congestive heart failure. However, the molecular mechanisms by which the direct actions of Ang II on cardiomyocytes contribute to ECC remodeling are not precisely known. This question was addressed using cardiac myocytes isolated from transgenic (TG1306/1R [TG]) mice exhibiting cardiac specific overexpression of angiotensinogen, which develop Ang II-mediated cardiac hypertrophy in the absence of hemodynamic overload. Electrophysiological techniques, photolysis of caged Ca 2ϩ and confocal Ca 2ϩ imaging were used to examine ECC remodeling at early (Ϸ20 weeks of age) and late (Ϸ60 weeks of age) time points during the development of cardiac dysfunction. In young TG mice, increased cardiac Ang II levels induced a hypertrophic response in cardiomyocyte, which was accompanied by an adaptive change of Ca 2ϩ signaling, specifically an upregulation of the Na ϩ /Ca 2ϩ exchangermediated Ca 2ϩ transport. In contrast, maladaptation was evident in older TG mice, as suggested by reduced sarcoplasmic reticulum Ca 2ϩ content resulting from a shift in the ratio of plasmalemmal Ca 2ϩ removal and sarcoplasmic reticulum Ca 2ϩ uptake. This was associated with a conserved ECC gain, consistent with a state of hypersensitivity in Ca 2ϩ-induced Ca 2ϩ release. Together, our data suggest that chronic elevation of cardiac Ang II levels significantly alters cardiomyocyte ECC in the long term, and thereby contractility, independently of hemodynamic overload and arterial hypertension.

Permissions: Requests for permissions to reproduce figures, tables, or portions of articles origi... more Permissions: Requests for permissions to reproduce figures, tables, or portions of articles originally published in Circulation Research can be obtained via RightsLink, a service of the Copyright Clearance Center, not the Editorial Office. Once the online version of the published article for which permission is being requested is located, click Request Permissions in the middle column of the Web page under Services. Further information about this process is available in the Permissions and Rights Question and Answer document. Reprints: Information about reprints can be found online at:

Circulation Research, 2009

, issue, in Figure 2, the second row, left panel, the integral for the NCX current was mistakenly... more , issue, in Figure 2, the second row, left panel, the integral for the NCX current was mistakenly omitted. Also in Figure 2, the second row, panel C, below the last two bar graphs, the integral for the NCX current (in brackets) was mistakenly omitted. These omissions have been corrected in the figure that is printed below. The authors regret the error.

Biophysical Journal, 2018

Detection and Classification of Ca 2+ Release Events in Confocal Line-and Frame-scan Images,

Cardiovascular Research, 2017

Enhanced inositol 1,4,5-trisphosphate receptor (InsP 3 R2) expression has been associated with a ... more Enhanced inositol 1,4,5-trisphosphate receptor (InsP 3 R2) expression has been associated with a variety of proarrhythmogenic cardiac disorders. The functional interaction between the two major Ca 2þ release mechanisms in cardiomyocytes, Ca 2þ release mediated by ryanodine receptors (RyR2s) and InsP 3-induced intracellular Ca 2þ release (IP3ICR) remains enigmatic. We aimed at identifying characterizing local IP3ICR events, and elucidating functional local crosstalk mechanisms between cardiac InsP 3 R2s and RyR2s under conditions of enhanced cardiac specific InsP 3 R2 activity.

Biophysical Journal, 2017

spectroscopic probes to those sites. Ryanodine binding measurements are performed to ensure funct... more spectroscopic probes to those sites. Ryanodine binding measurements are performed to ensure functional integrity of labeled CaM constructs. Then, we measure changes in intra-CaM distance distributions using time-resolved FRET or DEER. Our previous studies employed DEER of isolated CaM. Now, we rely on time-resolved FRET, to resolve structural changes of CaM bound to functional RyR in sarcoplasmic reticulum membranes. We will compare these measurements with those of CaM bound to a peptide corresponding to the CaM-binding domain of RyR (RyR1 residues: 3614-3643).

Increased Exchange Current but Normal Ca

Hypertrophied and failing cardiac myocytes generally show alterations in intracellular Ca handlin... more Hypertrophied and failing cardiac myocytes generally show alterations in intracellular Ca handling associated with changes in the contractile function and arrhythmogenicity. The cardiac Na exchange (NCX) is an important mechanism for Ca extrusion and cell relaxation. Its possible involvement in changes of excitation-contraction coupling (EC-coupling) with disease remains uncertain. We analyzed the NCX function in rat ventricular myocytes 5 to 6 months after experimental myocardial infarction (PMI) produced by left coronary artery ligation and from sham-operated (SO) hearts. Caged Ca was dialyzed into the cytoplasm via a patch-clamp pipette and Ca was released by flash photolysis to activate NCX and measure the associated currents (I NaCa ), whereas [Ca ] i changes were simultaneously recorded with a confocal microscope. I NaCa density normalized to the [Ca ] i jumps was 2.6-fold higher in myocytes from PMI rats. The level of total NCX protein expression in PMI myocytes was also incr...

Na+/Ca2+ exchange activity in the post-myocardial infarction rat model

Adaptive and Maladaptive Remodeling of Cardiomyocyte Excitation-Contraction Coupling by Angiotensin II

Trends in Cardiovascular Medicine, 2010

Chronic elevation of plasma angiotensin II (Ang II) is a major determinant in the pathogenesis of... more Chronic elevation of plasma angiotensin II (Ang II) is a major determinant in the pathogenesis of cardiac hypertrophy and congestive heart failure. However, the molecular mechanisms by which the direct actions of Ang II on cardiomyocytes contribute to excitation-contraction coupling (ECC) remodeling are not precisely known. We review this question, as well as acute Ang II-mediated modulation of ECC. In addition, we discuss adaptive/maladaptive modulation of cardiomyocyte ECC under chronic endogenous Ang II overproduction in the heart induced by local overexpression of the of the renin-angiotensin system in the mouse.

The Journal of Physiology, 1999

Circulation Research, 2002

Hypertrophied and failing cardiac myocytes generally show alterations in intracellular Ca 2+ hand... more Hypertrophied and failing cardiac myocytes generally show alterations in intracellular Ca 2+ handling associated with changes in the contractile function and arrhythmogenicity. The cardiac Na + -Ca 2+ exchange (NCX) is an important mechanism for Ca 2+ extrusion and cell relaxation. Its possible involvement in changes of excitation-contraction coupling (EC-coupling) with disease remains uncertain. We analyzed the NCX function in rat ventricular myocytes 5 to 6 months after experimental myocardial infarction (PMI) produced by left coronary artery ligation and from sham-operated (SO) hearts. Caged Ca 2+ was dialyzed into the cytoplasm via a patch-clamp pipette and Ca 2+ was released by flash photolysis to activate NCX and measure the associated currents ( I NaCa ), whereas [Ca 2+ ] i changes were simultaneously recorded with a confocal microscope. I NaCa density normalized to the [Ca 2+ ] i jumps was 2.6-fold higher in myocytes from PMI rats. The level of total NCX protein expression i...

Biophysical Journal, 2018

In cardiac muscle, besides Ca 2þ-induced Ca 2þ release (CICR), a second Ca 2þ release mechanism a... more In cardiac muscle, besides Ca 2þ-induced Ca 2þ release (CICR), a second Ca 2þ release mechanism activated by hormone binding to G-protein coupled receptors is present. This prompt intracellular production of the signaling molecule Inositol-1,4,5-trisphosphate (IP 3) which then subsequently triggers sarcoplasmic reticulum (SR)-Ca 2þ release through openings of IP 3 receptors type 2 (IP 3 R2s). IP 3-induced SR-Ca 2þ release (IP 3 ICR) may modulate Ryanodine receptor (RyR2s) function via locally regulated interactions and fine-tune excitation-contraction coupling in ventricular myocytes. A functional local interplay between IP 3 R2s and RyR2s may be significantly pronounced under several cardiac pathologies where IP 3 R2 has been found to be overexpressed. We examined IP 3 ICR and CICR in ventricular myocytes on a local scale in a cardiac specific IP 3 R2-overexpressing mouse model (IP 3 /tTA) with a phenotype of cardiac hypertrophy. Protein analysis confirmed a 12-fold increase in IP 3 R2 expression together with a reduction in RyR2 protein levels by 61.7%. IP 3pathway stimulation in wild-type permeabilized cells increased spontaneous Ca 2þ events by 24.2%. Surprisingly, activation of IP 3 ICR in IP 3 /tTA myocytes induced a decrease in Ca 2þ spark frequency by 25.2% together with a reduction of the SR-Ca 2þ content by 14.4% that cannot be explained by RyR2 Ca 2þ spark occurrence alone. We examined this phenomenon in more detail in intact myocytes by applying specific SR-Ca 2þ leak/load protocols. We found that in IP 3 /tTA mice IP 3 ICR functions below the threshold for Ca 2þ sparks, via efficient modulation of the SR-Ca 2þ leak. Activation of this pathway acts as a protective mechanism against arrhythmogenic Ca 2þ wave occurrence. We conclude that the overexpression of IP 3 R2 in ventricular myocytes may represent a new and so far not recognized antiarrhythmogenic mechanism that can prevent SR-Ca 2þ overload and reduce the propensity of aberrant SR-Ca 2þ release preconditioned for arrhythmogenicity. This mechanism could be a potential target for precision medicine therapies treating ventricular tachycardia.

Cell Calcium, 2005

Antisense oligodeoxynucleotides (AS-ODNs) were used in combination with transient functional expr... more Antisense oligodeoxynucleotides (AS-ODNs) were used in combination with transient functional expression of the cardiac Na +-Ca 2+ exchanger (NCX1) to correlate suppression of the Na +-Ca 2+ exchange function with down-regulation of NCX1 protein expression. In a denovo expression system (Sf9 cells), a decrease in both, NCX1 mRNA and protein after AS-ODN application was paralleled by diminished NCX1 activity, a typical hallmark of a true "antisense effect". Although AS-ODN uptake was also efficient in rat neonatal cardiac myocytes, in wholecell extracts of these cells treated with AS-ODNs, the amount of NCX1 protein determined in a quantitative binding assay remained almost unchanged, despite a prompt loss of NCX1 function. Immunocytochemical staining of myocytes revealed that most of the immunoreactivity was not localized in the plasma membrane, but in intracellular compartments and was barely affected by AS-ODN treatment. These results indicate that the "functional half-life" of the NCX1 protein in the plasma membrane of neonatal cardiac myocytes is surprisingly short, much shorter than reported half-lifes of about 30 h for other membrane proteins.

Lipid and lipid-protein monolayers spread from a vesicle suspension: a microfluorescence film balance study

The Journal of Physical Chemistry, 1990

... Figure 5b shows the corresponding green (fluorescein) fluorescence pattern. ... The congruenc... more ... Figure 5b shows the corresponding green (fluorescein) fluorescence pattern. ... The congruency of the red and green fluorescence pattern shows that the Fab' fragment bound to the membrane retained its function throughout the reconstitution process. ...

Calcium signalling in cardiac muscle: refractoriness revealed by coherent activation

Nature cell biology, 1999

Contraction of cardiac myocytes is governed by calcium-ion (Ca2+ )-induced Ca2+ release (CICR) fr... more Contraction of cardiac myocytes is governed by calcium-ion (Ca2+ )-induced Ca2+ release (CICR) from the sarcoplasmic reticulum through Ca2+-release channels. Ca2+ release occurs by concerted activation of numerous elementary Ca2+ events, 'Ca2+ sparks', that are triggered and locally controlled by Ca2+ influx into the cell through plasmalemmal L-type Ca2+ channels. Because of the positive feedback inherent in CICR, an as-yet-unidentified control mechanism is required to restrain the amplification of Ca2+ signalling and to terminate Ca2+ release from the sarcoplasmic reticulum. Here we use ultraviolet-laser-flash and two-photon photolysis of caged Ca2+ to study spatiotemporal features of the termination and refractoriness of Ca2+ release. Coherent and simultaneous activation of all Ca2+-release sites within a cardiac myocyte unmasked a prominent refractoriness, recovering monotonically within about 1 second. In contrast, selective activation of a few Ca 2+-release sites was no...

Uptake-leak balance of SR Ca2+ determines arrhythmogenic potential of RyR2R420Q+/− cardiomyocytes

Journal of Molecular and Cellular Cardiology

Journal of Molecular and Cellular Cardiology, 2020

Impairment of vascular responsiveness to nitric-oxide (NO•), or NO-resistance, occurs in many car... more Impairment of vascular responsiveness to nitric-oxide (NO•), or NO-resistance, occurs in many cardiovascular diseases. It is prominent especially in poorly-controlled diabetic individuals. We investigated HNO donor, isopropylamine NONOate (IPA-NO), offers haemodynamic advantages over the NO• donor, diethylamine NONOate (DEA-NO), in diabetic myocardium. After 8-weeks of streptozotocin diabetes (55 mg/kg i.v.) or citrate-vehicle sham (n = 12-16/group), hearts were isolated from anesthetized adult male rats (ketamine-xylazine 100-12 mg/kg, i.p.) and Langendorff-perfused. Following U46619 pre-constriction of the coronary vasculature to 50% of basal flow, dose-response curves to acute bolus doses of IPA-NO or DEA-NO (10 pmol-10 μmol) were performed. Blood glucose levels (31 ± 2 mM) were markedly elevated, body weight (291 ± 5 g) was significantly lower, in diabetic rats compared to sham (blood glucose 9 ± 1 mM, body weight 460 ± 5 g). Diabetes impaired NO•-induced LV-maximal relaxation by 50% (↓LV-dP/dt 150 ± 8 mmHg/s), LV-maximal contractile function by 22% (↑LV + dP/dt 322 ± 14 mmHg/s) and maximal coronary vasodilatation by 32% (↑4.2 ± 0.2 ml/min), compared to non-diabetic counterparts (↓LV-dP/dt 300 ± 10 mmHg/s, ↑LV + dP/dt 410 ± 10 mmHg/s, coronary-flow ↑5.8 ± 0.52 ml/min, p b .05). In contrast, HNO enhanced LV-maximum relaxation by 40% (↓LV-dP/dt 280 ± 10 mmHg/s) and LV-contractile function by 120% (↑LV + dP/dt 260 ± 20 mmHg/s), with preserved vasodilation (↑4.1 ± 0.1 ml/min) in diabetic myocardium, compared to non-diabetic counterparts (↓LV-dP/dt 200 ± 13 mmHg/s, ↑LV + dP/dt 120 ± 15 mmHg/s, coronary-flow ↑4.0 ± 0.2 ml/min, p b .05). These results provide the first evidence that NOresistance occurs in diabetic myocardium, and HNO largely circumvents this phenomena. These results support potential roles for therapeutic HNO administration in acute treatment of heart disease in diabetes.

Poster: Automatic detection, characterization, and classification of local Ca2+ release events in... more Poster: Automatic detection, characterization, and classification of local Ca2+ release events in cardiomyocytes

Ca2+ waves and the arrhythmogenicity paradigm: role of SERCA stimulation in a CPVT mouse model

Biophysical Journal, 2022

Bulletin des Médecins Suisses, 2022

Cardiac hypertrophy is associated with alterations in cardiomyocyte excitation-contraction coupli... more Cardiac hypertrophy is associated with alterations in cardiomyocyte excitation-contraction coupling (ECC) and Ca 2ϩ handling. Chronic elevation of plasma angiotensin II (Ang II) is a major determinant in the pathogenesis of cardiac hypertrophy and congestive heart failure. However, the molecular mechanisms by which the direct actions of Ang II on cardiomyocytes contribute to ECC remodeling are not precisely known. This question was addressed using cardiac myocytes isolated from transgenic (TG1306/1R [TG]) mice exhibiting cardiac specific overexpression of angiotensinogen, which develop Ang II-mediated cardiac hypertrophy in the absence of hemodynamic overload. Electrophysiological techniques, photolysis of caged Ca 2ϩ and confocal Ca 2ϩ imaging were used to examine ECC remodeling at early (Ϸ20 weeks of age) and late (Ϸ60 weeks of age) time points during the development of cardiac dysfunction. In young TG mice, increased cardiac Ang II levels induced a hypertrophic response in cardiomyocyte, which was accompanied by an adaptive change of Ca 2ϩ signaling, specifically an upregulation of the Na ϩ /Ca 2ϩ exchangermediated Ca 2ϩ transport. In contrast, maladaptation was evident in older TG mice, as suggested by reduced sarcoplasmic reticulum Ca 2ϩ content resulting from a shift in the ratio of plasmalemmal Ca 2ϩ removal and sarcoplasmic reticulum Ca 2ϩ uptake. This was associated with a conserved ECC gain, consistent with a state of hypersensitivity in Ca 2ϩ-induced Ca 2ϩ release. Together, our data suggest that chronic elevation of cardiac Ang II levels significantly alters cardiomyocyte ECC in the long term, and thereby contractility, independently of hemodynamic overload and arterial hypertension.

Permissions: Requests for permissions to reproduce figures, tables, or portions of articles origi... more Permissions: Requests for permissions to reproduce figures, tables, or portions of articles originally published in Circulation Research can be obtained via RightsLink, a service of the Copyright Clearance Center, not the Editorial Office. Once the online version of the published article for which permission is being requested is located, click Request Permissions in the middle column of the Web page under Services. Further information about this process is available in the Permissions and Rights Question and Answer document. Reprints: Information about reprints can be found online at:

Circulation Research, 2009

, issue, in Figure 2, the second row, left panel, the integral for the NCX current was mistakenly... more , issue, in Figure 2, the second row, left panel, the integral for the NCX current was mistakenly omitted. Also in Figure 2, the second row, panel C, below the last two bar graphs, the integral for the NCX current (in brackets) was mistakenly omitted. These omissions have been corrected in the figure that is printed below. The authors regret the error.

Biophysical Journal, 2018

Detection and Classification of Ca 2+ Release Events in Confocal Line-and Frame-scan Images,

Cardiovascular Research, 2017

Enhanced inositol 1,4,5-trisphosphate receptor (InsP 3 R2) expression has been associated with a ... more Enhanced inositol 1,4,5-trisphosphate receptor (InsP 3 R2) expression has been associated with a variety of proarrhythmogenic cardiac disorders. The functional interaction between the two major Ca 2þ release mechanisms in cardiomyocytes, Ca 2þ release mediated by ryanodine receptors (RyR2s) and InsP 3-induced intracellular Ca 2þ release (IP3ICR) remains enigmatic. We aimed at identifying characterizing local IP3ICR events, and elucidating functional local crosstalk mechanisms between cardiac InsP 3 R2s and RyR2s under conditions of enhanced cardiac specific InsP 3 R2 activity.

Biophysical Journal, 2017

spectroscopic probes to those sites. Ryanodine binding measurements are performed to ensure funct... more spectroscopic probes to those sites. Ryanodine binding measurements are performed to ensure functional integrity of labeled CaM constructs. Then, we measure changes in intra-CaM distance distributions using time-resolved FRET or DEER. Our previous studies employed DEER of isolated CaM. Now, we rely on time-resolved FRET, to resolve structural changes of CaM bound to functional RyR in sarcoplasmic reticulum membranes. We will compare these measurements with those of CaM bound to a peptide corresponding to the CaM-binding domain of RyR (RyR1 residues: 3614-3643).

Increased Exchange Current but Normal Ca

Hypertrophied and failing cardiac myocytes generally show alterations in intracellular Ca handlin... more Hypertrophied and failing cardiac myocytes generally show alterations in intracellular Ca handling associated with changes in the contractile function and arrhythmogenicity. The cardiac Na exchange (NCX) is an important mechanism for Ca extrusion and cell relaxation. Its possible involvement in changes of excitation-contraction coupling (EC-coupling) with disease remains uncertain. We analyzed the NCX function in rat ventricular myocytes 5 to 6 months after experimental myocardial infarction (PMI) produced by left coronary artery ligation and from sham-operated (SO) hearts. Caged Ca was dialyzed into the cytoplasm via a patch-clamp pipette and Ca was released by flash photolysis to activate NCX and measure the associated currents (I NaCa ), whereas [Ca ] i changes were simultaneously recorded with a confocal microscope. I NaCa density normalized to the [Ca ] i jumps was 2.6-fold higher in myocytes from PMI rats. The level of total NCX protein expression in PMI myocytes was also incr...

Na+/Ca2+ exchange activity in the post-myocardial infarction rat model

Adaptive and Maladaptive Remodeling of Cardiomyocyte Excitation-Contraction Coupling by Angiotensin II

Trends in Cardiovascular Medicine, 2010

Chronic elevation of plasma angiotensin II (Ang II) is a major determinant in the pathogenesis of... more Chronic elevation of plasma angiotensin II (Ang II) is a major determinant in the pathogenesis of cardiac hypertrophy and congestive heart failure. However, the molecular mechanisms by which the direct actions of Ang II on cardiomyocytes contribute to excitation-contraction coupling (ECC) remodeling are not precisely known. We review this question, as well as acute Ang II-mediated modulation of ECC. In addition, we discuss adaptive/maladaptive modulation of cardiomyocyte ECC under chronic endogenous Ang II overproduction in the heart induced by local overexpression of the of the renin-angiotensin system in the mouse.

The Journal of Physiology, 1999

Circulation Research, 2002

Hypertrophied and failing cardiac myocytes generally show alterations in intracellular Ca 2+ hand... more Hypertrophied and failing cardiac myocytes generally show alterations in intracellular Ca 2+ handling associated with changes in the contractile function and arrhythmogenicity. The cardiac Na + -Ca 2+ exchange (NCX) is an important mechanism for Ca 2+ extrusion and cell relaxation. Its possible involvement in changes of excitation-contraction coupling (EC-coupling) with disease remains uncertain. We analyzed the NCX function in rat ventricular myocytes 5 to 6 months after experimental myocardial infarction (PMI) produced by left coronary artery ligation and from sham-operated (SO) hearts. Caged Ca 2+ was dialyzed into the cytoplasm via a patch-clamp pipette and Ca 2+ was released by flash photolysis to activate NCX and measure the associated currents ( I NaCa ), whereas [Ca 2+ ] i changes were simultaneously recorded with a confocal microscope. I NaCa density normalized to the [Ca 2+ ] i jumps was 2.6-fold higher in myocytes from PMI rats. The level of total NCX protein expression i...

Biophysical Journal, 2018

In cardiac muscle, besides Ca 2þ-induced Ca 2þ release (CICR), a second Ca 2þ release mechanism a... more In cardiac muscle, besides Ca 2þ-induced Ca 2þ release (CICR), a second Ca 2þ release mechanism activated by hormone binding to G-protein coupled receptors is present. This prompt intracellular production of the signaling molecule Inositol-1,4,5-trisphosphate (IP 3) which then subsequently triggers sarcoplasmic reticulum (SR)-Ca 2þ release through openings of IP 3 receptors type 2 (IP 3 R2s). IP 3-induced SR-Ca 2þ release (IP 3 ICR) may modulate Ryanodine receptor (RyR2s) function via locally regulated interactions and fine-tune excitation-contraction coupling in ventricular myocytes. A functional local interplay between IP 3 R2s and RyR2s may be significantly pronounced under several cardiac pathologies where IP 3 R2 has been found to be overexpressed. We examined IP 3 ICR and CICR in ventricular myocytes on a local scale in a cardiac specific IP 3 R2-overexpressing mouse model (IP 3 /tTA) with a phenotype of cardiac hypertrophy. Protein analysis confirmed a 12-fold increase in IP 3 R2 expression together with a reduction in RyR2 protein levels by 61.7%. IP 3pathway stimulation in wild-type permeabilized cells increased spontaneous Ca 2þ events by 24.2%. Surprisingly, activation of IP 3 ICR in IP 3 /tTA myocytes induced a decrease in Ca 2þ spark frequency by 25.2% together with a reduction of the SR-Ca 2þ content by 14.4% that cannot be explained by RyR2 Ca 2þ spark occurrence alone. We examined this phenomenon in more detail in intact myocytes by applying specific SR-Ca 2þ leak/load protocols. We found that in IP 3 /tTA mice IP 3 ICR functions below the threshold for Ca 2þ sparks, via efficient modulation of the SR-Ca 2þ leak. Activation of this pathway acts as a protective mechanism against arrhythmogenic Ca 2þ wave occurrence. We conclude that the overexpression of IP 3 R2 in ventricular myocytes may represent a new and so far not recognized antiarrhythmogenic mechanism that can prevent SR-Ca 2þ overload and reduce the propensity of aberrant SR-Ca 2þ release preconditioned for arrhythmogenicity. This mechanism could be a potential target for precision medicine therapies treating ventricular tachycardia.

Cell Calcium, 2005

Antisense oligodeoxynucleotides (AS-ODNs) were used in combination with transient functional expr... more Antisense oligodeoxynucleotides (AS-ODNs) were used in combination with transient functional expression of the cardiac Na +-Ca 2+ exchanger (NCX1) to correlate suppression of the Na +-Ca 2+ exchange function with down-regulation of NCX1 protein expression. In a denovo expression system (Sf9 cells), a decrease in both, NCX1 mRNA and protein after AS-ODN application was paralleled by diminished NCX1 activity, a typical hallmark of a true "antisense effect". Although AS-ODN uptake was also efficient in rat neonatal cardiac myocytes, in wholecell extracts of these cells treated with AS-ODNs, the amount of NCX1 protein determined in a quantitative binding assay remained almost unchanged, despite a prompt loss of NCX1 function. Immunocytochemical staining of myocytes revealed that most of the immunoreactivity was not localized in the plasma membrane, but in intracellular compartments and was barely affected by AS-ODN treatment. These results indicate that the "functional half-life" of the NCX1 protein in the plasma membrane of neonatal cardiac myocytes is surprisingly short, much shorter than reported half-lifes of about 30 h for other membrane proteins.

Lipid and lipid-protein monolayers spread from a vesicle suspension: a microfluorescence film balance study

The Journal of Physical Chemistry, 1990

... Figure 5b shows the corresponding green (fluorescein) fluorescence pattern. ... The congruenc... more ... Figure 5b shows the corresponding green (fluorescein) fluorescence pattern. ... The congruency of the red and green fluorescence pattern shows that the Fab' fragment bound to the membrane retained its function throughout the reconstitution process. ...

Calcium signalling in cardiac muscle: refractoriness revealed by coherent activation

Nature cell biology, 1999

Contraction of cardiac myocytes is governed by calcium-ion (Ca2+ )-induced Ca2+ release (CICR) fr... more Contraction of cardiac myocytes is governed by calcium-ion (Ca2+ )-induced Ca2+ release (CICR) from the sarcoplasmic reticulum through Ca2+-release channels. Ca2+ release occurs by concerted activation of numerous elementary Ca2+ events, 'Ca2+ sparks', that are triggered and locally controlled by Ca2+ influx into the cell through plasmalemmal L-type Ca2+ channels. Because of the positive feedback inherent in CICR, an as-yet-unidentified control mechanism is required to restrain the amplification of Ca2+ signalling and to terminate Ca2+ release from the sarcoplasmic reticulum. Here we use ultraviolet-laser-flash and two-photon photolysis of caged Ca2+ to study spatiotemporal features of the termination and refractoriness of Ca2+ release. Coherent and simultaneous activation of all Ca2+-release sites within a cardiac myocyte unmasked a prominent refractoriness, recovering monotonically within about 1 second. In contrast, selective activation of a few Ca 2+-release sites was no...