KCNQ1 channels sense small changes in cell volume (original) (raw)
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Modulation of KCNQ4 channel activity by changes in cell volume
Biochimica et Biophysica Acta (BBA) - Biomembranes, 2004
KCNQ4 channels expressed in HEK 293 cells are sensitive to cell volume changes, being activated by swelling and inhibited by shrinkage, respectively. The KCNQ4 channels contribute significantly to the regulatory volume decrease (RVD) process following cell swelling. Under isoosmotic conditions, the KCNQ4 channel activity is modulated by protein kinases A and C, G protein activation, and a reduction in the intracellular Ca 2 + concentration, but these signalling pathways are not responsible for the increased channel activity during cell swelling. D
Regulation of cloned, Ca2+-activated K+ channels by cell volume changes
Pflügers Archiv, 2002
Ca 2+ -activated K + channels of big (hBK), intermediate (hIK) or small (rSK3) conductance were coexpressed with aquaporin 1 (AQP1) in Xenopus laevis oocytes. hBK channels were activated by depolarization, whereas hIK and rSK3 channels were activated by direct injection of Ca 2+ or Cd 2+ into the oocyte cytoplasm, before the oocytes were subjected to hyperosmolar or hypoosmolar (±50 mOsm mannitol) challenges. In all cases, the oocytes responded rapidly to the osmotic changes with shrinkage or swelling and the effects on the K + currents were measured. hIK and rSK3 currents were highly sensitive to volume changes and increased immediately to 178% (hIK) or 165% (rSK3) of control in response to swelling and decreased to 64% (hIK) or 61% (rSK3) of control after shrinkage. These responses were dependent on the channels being pre-activated and were almost totally abolished after injection of cytochalasin D into the oocyte cytoplasm (final concentration: 1 µM). In contrast, hBK channels showed only a minor sensitivity to volume changes; the hBK channel activity decreased approximately 20% after swelling and increased approximately 20% after shrinkage. The opposite effects of volume changes on hIK/rSK3 and hBK channels suggest that the significant stimulation of hIK and rSK3 channels during swelling is not mediated by changes in intracellular Ca 2+ , but rather through interactions with the cytoskeleton, provided that a sufficient basal concentration of intracellular Ca 2+ or Cd 2+ is present.
The Journal of Membrane Biology, 1994
Agonists that elevate calcium in T84 cells stimulate chloride secretion by activating Kmc, an inwardly rectifying K channel in the basolateral membrane. We have studied the regulation of this channel by calcium, nucleotides and phosphorylation using patch clamp and short-circuit current (Isc) techniques. Open probability (Po) was independent of voltage but declined spontaneously with time after excision. Rundown was slower if patches were excised into a bath solution containing ATP (10 ~tM-5 rnM), ATP (0.1 rnM) + protein kinase A (PKA; 180 nM), or isobutylmethylxanthine (IBMX; 1 mM). Analysis of event durations suggested that the channel has at least two open and two closed states, and that rundown under control conditions is mainly due to prolongation of the long closed time. Channel activity was restimulated after rundown by exposure to ATP, the poorly hydrolyzable ATP analogue AMP-PNP, or ADP. Activity was further enhanced when PKA was added in the presence of MgATP, but only if free calcium concentration was elevated (400 nM). Nucleotide stimulation and inward rectification were both observed in nominally Mg-free solutions, cAMP modulation of basolateral potassium conductance in situ was confirmed by measuring currents generated by a transepithelial K gradient after permeabilization of the apical membrane using a-toxin. Finally, protein kinase C (PKC) inhibited single Kmc channels when it was added directly to excised patches. These results suggest that nonhydrolytic binding of nucleotides and phosphorylation by PKA and PKC modulate the responsiveness of the inwardly rectifying K channel to Ca-mediated secretagogues.
Expression of Potassium Channels in Epithelial Cells Depends on Calcium-activated Cell-Cell Contacts
Harvesting MDCK cells with trypsin-EDTA reduces potassium currents (IK) to a mere 10%, presumably by hydrolysis of K + channels, but replating at con-fluence restores them in 12-18 hr, through a process that requires transcription, translation and exocytic fusion of intracellular membrane vesicles to the plasma membrane (Ponce & Cereijido, 1991; Ponce et al., 1991a). In the present work we find that this restoration of I K also requires cell-cell contacts and the presence of 1.8 rnM Ca 2 § The role of extracellular Ca 2 § may be substituted by 2.0 gM TRH, 10 nM PMA or 200 gg/ml DiC8, drugs that stimulate the system of phospholipase C (PLC) and protein kinase C (PKC). Conversely, the recovery of IK triggered by Ca-dependent contacts can be blocked by 110 gM neomycin, 2.0 gM H7, and 250 nM staurosporine, inhibitors of PLC and PKC. These results suggest that the expression of new K + channels depends on Ca 2 § activated contacts with neighboring cells and that the information is conveyed through PLC and PKC, a process in keeping with changes in its enzymatic activity and cellular distribution of PKC. Plasma membrane is also reduced and restored upon harvesting and replating, and depends on Ca2+-activated contracts. However, the effects of the chemicals tested on I K differ from the ones they elicit on the recovery of plasma membrane, suggesting that cells can independently regulate their population of K + channels and the surface of their membrane.
Journal of Biological Chemistry, 2001
The gene KCNQ1 encodes a K + channel α-subunit important for cardiac repolarization, formerly known as K v LQT1. In large and small intestine a channel complex consisting of KCNQ1 and the β-subunit KCNE3 (MiRP2) is known to mediate the cAMP activated basolateral K + current which is essential for luminal Clsecretion. Northern blot experiments revealed an expression of both subunits in lung tissue. However previous reports suggested a role of KCNE1 (minK, Isk) but not KCNE3 in airway epithelial cells. Here we give evidence that KCNE1 is not detected in murine tracheal epithelial cells and that Clsecretion by these cells is not reduced by the knockout of the KCNE1 gene. In contrast we show that a complex consisting of KCNQ1 and KCNE3 probably forms a basolateral K + channel in murine tracheal epithelial cells. As described for colonic epithelium the current through KCNQ1 complexes in murine trachea is specifically inhibited by the chromanol 293B. A 293B sensitive current was present after stimulation with forskolin and agonists increasing Ca 2+ as well as after administration of the pharmacological K + channel activator 1-EBIO. A 293B-inhibitable current was already present under control conditions and reduced after administration of amiloride indicating a role of this K + channel not only for Clsecretion but also for Na + reabsorption. We conclude that at least in mice a KCNQ1 channel complex seems to be the dominant basolateral K + conductance in tracheal epithelial cells.
Journal of Biological Chemistry, 2010
The KCNE3 -subunit constitutively opens outwardly rectifying KCNQ1 (Kv7.1) K ؉ channels by abolishing their voltagedependent gating. The resulting KCNQ1/KCNE3 heteromers display enhanced sensitivity to K ؉ channel inhibitors like chromanol 293B. KCNE3 was also suggested to modify biophysical properties of several other K ؉ channels, and a mutation in KCNE3 was proposed to underlie forms of human periodic paralysis. To investigate physiological roles of KCNE3, we now disrupted its gene in mice. kcne3 ؊/؊ mice were viable and fertile and displayed neither periodic paralysis nor other obvious skeletal muscle abnormalities. KCNQ1/KCNE3 heteromers are present in basolateral membranes of intestinal and tracheal epithelial cells where they might facilitate transepithelial Cl ؊ secretion through basolateral recycling of K ؉ ions and by increasing the electrochemical driving force for apical Cl ؊ exit. Indeed, cAMP-stimulated electrogenic Cl ؊ secretion across tracheal and intestinal epithelia was drastically reduced in kcne3 ؊/؊ mice. Because the abundance and subcellular localization of KCNQ1 was unchanged in kcne3 ؊/؊ mice, the modification of biophysical properties of KCNQ1 by KCNE3 is essential for its role in intestinal and tracheal transport. Further, these results suggest KCNE3 as a potential modifier gene in cystic fibrosis. Voltage-gated K ϩ channels are tetramers of identical or homologous subunits that form a single, common ion-selective pore. In many K ϩ channels these complexes of pore-forming ␣-subunits associate with ancillary -subunits that may be cytosolic (1) or may span the lipid bilayer with one (2) or several (3) transmembrane domains. These -subunits may influence the subcellular trafficking of K ϩ channels or change their regulation and biophysical properties. The KCNE gene family of -subunits, which was identified by expression cloning in Xenopus oocytes (2), encodes five different proteins (KCNE1-5) that display a single transmembrane-spanning domain and an extracellular N terminus (for reviews see Refs. 4 and 5). Despite minK (minimal K channel, an old name for KCNE1) being a misnomer, KCNE2-KCNE5 are sometimes called MirP1-4 for MinK-related peptide (5, 6). In heterologous expression, KCNE proteins influence the properties of an astoundingly large number of different K ϩ channels (5). It is questionable whether all of these promiscuous interactions are of biological significance in vivo. The relevance of just a few of these interactions has been established beyond reasonable doubt. KCNQ1/KCNE1 heteromers mediate the slowly activating I Ks current of the myocardium and are involved in inner ear K ϩ secretion, as became evident from KCNE1 mutations in human cardiac arrhythmia and deafness (7-9) and from kcne1 knockout (KO) 2 mice (10, 11). The situation is less clear for KCNE2, which may modulate HERG (6), KCNQ1 (12), KCNQ2/3 (13), and Kv4 (14) K ϩ channels. Variants in the KCNE2 gene may cause human cardiac arrhythmia by altering HERG currents (6), but kcne2 Ϫ/Ϫ mice rather showed reduced cardiac Kv1.5 and Kv4.2 currents (15). KCNQ1/KCNE2 heteromers are important for gastric acid secretion as revealed by kcnq1 Ϫ/Ϫ (16-18) and kcne2 Ϫ/Ϫ mice (19). Whereas KCNE1 significantly slows and enhances the depolarization-induced activation of KCNQ1 currents (20, 21), KCNE3 abolishes its voltage dependence. KCNQ1/KCNE3 heteromers yield instantaneous, nearly ohmic whole cell currents (22). Similar effects on gating were observed with KCNQ1/ KCNE2 co-expression, although current amplitudes were much smaller (12, 23). Either -subunit affects the movement of the voltage-sensing S4 domain of KCNQ1 (24). KCNQ1/ KCNE3 currents could be stimulated by cAMP (22) and showed increased sensitivity to the inhibitors chromanol 293B and clotrimazole (22), as well as to XE991 (25). KCNE3 did not affect KCNQ2/3 but suppressed KCNQ4 and HERG currents (22). KCNE3 was also reported to interact with Kv2.1, Kv3.1, and Kv3.2 K ϩ channels (26, 27) in brain and with Kv3.4 in skeletal muscle (28). In situ hybridization (22) and immunofluorescence (29) revealed co-expression of KCNQ1 and KCNE3 in intestinal epithelial cells. This led to the speculation that KCNQ1/KCNE3 mediates the chromanol 293B-and clotrima-* This work was supported in part by the Prix Louis Jeantet de Mé decine (to T. J. J.
Journal of Biological Chemistry, 2010
The KCNE3 -subunit constitutively opens outwardly rectifying KCNQ1 (Kv7.1) K ؉ channels by abolishing their voltagedependent gating. The resulting KCNQ1/KCNE3 heteromers display enhanced sensitivity to K ؉ channel inhibitors like chromanol 293B. KCNE3 was also suggested to modify biophysical properties of several other K ؉ channels, and a mutation in KCNE3 was proposed to underlie forms of human periodic paralysis. To investigate physiological roles of KCNE3, we now disrupted its gene in mice. kcne3 ؊/؊ mice were viable and fertile and displayed neither periodic paralysis nor other obvious skeletal muscle abnormalities. KCNQ1/KCNE3 heteromers are present in basolateral membranes of intestinal and tracheal epithelial cells where they might facilitate transepithelial Cl ؊ secretion through basolateral recycling of K ؉ ions and by increasing the electrochemical driving force for apical Cl ؊ exit. Indeed, cAMP-stimulated electrogenic Cl ؊ secretion across tracheal and intestinal epithelia was drastically reduced in kcne3 ؊/؊ mice. Because the abundance and subcellular localization of KCNQ1 was unchanged in kcne3 ؊/؊ mice, the modification of biophysical properties of KCNQ1 by KCNE3 is essential for its role in intestinal and tracheal transport. Further, these results suggest KCNE3 as a potential modifier gene in cystic fibrosis. Voltage-gated K ϩ channels are tetramers of identical or homologous subunits that form a single, common ion-selective pore. In many K ϩ channels these complexes of pore-forming ␣-subunits associate with ancillary -subunits that may be cytosolic (1) or may span the lipid bilayer with one (2) or several (3) transmembrane domains. These -subunits may influence the subcellular trafficking of K ϩ channels or change their regulation and biophysical properties. The KCNE gene family of -subunits, which was identified by expression cloning in Xenopus oocytes (2), encodes five different proteins (KCNE1-5) that display a single transmembrane-spanning domain and an extracellular N terminus (for reviews see Refs. 4 and 5). Despite minK (minimal K channel, an old name for KCNE1) being a misnomer, KCNE2-KCNE5 are sometimes called MirP1-4 for MinK-related peptide (5, 6). In heterologous expression, KCNE proteins influence the properties of an astoundingly large number of different K ϩ channels (5). It is questionable whether all of these promiscuous interactions are of biological significance in vivo. The relevance of just a few of these interactions has been established beyond reasonable doubt. KCNQ1/KCNE1 heteromers mediate the slowly activating I Ks current of the myocardium and are involved in inner ear K ϩ secretion, as became evident from KCNE1 mutations in human cardiac arrhythmia and deafness (7-9) and from kcne1 knockout (KO) 2 mice (10, 11). The situation is less clear for KCNE2, which may modulate HERG (6), KCNQ1 (12), KCNQ2/3 (13), and Kv4 (14) K ϩ channels. Variants in the KCNE2 gene may cause human cardiac arrhythmia by altering HERG currents (6), but kcne2 Ϫ/Ϫ mice rather showed reduced cardiac Kv1.5 and Kv4.2 currents (15). KCNQ1/KCNE2 heteromers are important for gastric acid secretion as revealed by kcnq1 Ϫ/Ϫ (16-18) and kcne2 Ϫ/Ϫ mice (19). Whereas KCNE1 significantly slows and enhances the depolarization-induced activation of KCNQ1 currents (20, 21), KCNE3 abolishes its voltage dependence. KCNQ1/KCNE3 heteromers yield instantaneous, nearly ohmic whole cell currents (22). Similar effects on gating were observed with KCNQ1/ KCNE2 co-expression, although current amplitudes were much smaller (12, 23). Either -subunit affects the movement of the voltage-sensing S4 domain of KCNQ1 (24). KCNQ1/ KCNE3 currents could be stimulated by cAMP (22) and showed increased sensitivity to the inhibitors chromanol 293B and clotrimazole (22), as well as to XE991 (25). KCNE3 did not affect KCNQ2/3 but suppressed KCNQ4 and HERG currents (22). KCNE3 was also reported to interact with Kv2.1, Kv3.1, and Kv3.2 K ϩ channels (26, 27) in brain and with Kv3.4 in skeletal muscle (28). In situ hybridization (22) and immunofluorescence (29) revealed co-expression of KCNQ1 and KCNE3 in intestinal epithelial cells. This led to the speculation that KCNQ1/KCNE3 mediates the chromanol 293B-and clotrima-* This work was supported in part by the Prix Louis Jeantet de Mé decine (to T. J. J.
Molecular diversity and function of K+ channels in airway and alveolar epithelial cells
AJP: Lung Cellular and Molecular Physiology, 2008
Multiple K+ channels are expressed in the respiratory epithelium lining airways and alveoli. Of the three main classes [ 1) voltage-dependent or Ca2+-activated, 6-transmembrane domains (TMD), 2) 2-pores 4-TMD, and 3) inward-rectified 2-TMD K+ channels], almost 40 different transcripts have already been detected in the lung. The physiological and functional significance of this high molecular diversity of lung epithelial K+ channels is intriguing. As detailed in the present review, K+ channels are located at both the apical and basolateral membranes in the respiratory epithelium, where they mediate K+ currents of diverse electrophysiological and regulatory properties. The main recognized function of K+ channels is to control membrane potential and to maintain the driving force for transepithelial ion and liquid transport. In this manner, KvLQT1, KCa and KATP channels, for example, contribute to the control of airway and alveolar surface liquid composition and volume. Thus, K+ channel...
Electrophysiological and molecular identification of hepatocellular volume-activated K channels
Biochimica et Biophysica Acta (BBA) - Biomembranes, 2005
Although K + channels are essential for hepatocellular function, it is not known which channels are involved in the regulatory volume decrease (RVD) in these cells. We have used a combination of electrophysiological and molecular approaches to describe the potential candidates for these channels. The dialysis of short-term cultured rat hepatocytes with a hypotonic solution containing high K + and low Cl À concentration caused the slow activation of an outward, time-independent current under whole-cell configuration of the patch electrode voltage clamp. The reversal potential of this current suggested that K + was the primary charge carrier. The swelling-induced K + current (I Kvol ) occurred in the absence of Ca 2+ and was inhibited with 1 AM Ca 2+ in the pipette solution. The activation of I Kvol required both Mg 2+ and ATP and an increasing concentration of Mg-ATP from 0.25 through 0.5 to 0.9 mM activated I Kvol increasingly faster and to a larger extent. The KCNQ1 inhibitor chromanol 293B reversibly depressed I Kvol with an IC 50 of 26 AM. RT-PCR detected the expression of members of the KCNQ family from KCNQ1 to KCNQ5 and of the accessory proteins KCNE1 to KCNE3 in the rat hepatocytes, but not KCNQ2 and KCNE2 in human liver. Western blotting showed KCNE3 expression in a plasma membrane-enriched fraction from rat hepatocytes. The results suggest that KCNQ1, probably with KCNE2 or KCNE3 as its accessory unit, provides a significant fraction of I Kvol in rat hepatocytes. D