Electrophysiological properties of the hypokalaemic periodic paralysis mutation (R528H) of the skeletal muscle α1S subunit as expressed in mouse L cells (original) (raw)
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Molecular Properties of Calcium Channels in Skeletal Muscle and Neurons
Annals of the New York Academy of Sciences, 1993
MOLECULAR PROPERTIES OF L-TYPE CALCIUM CHANNELS Four classes of voltage-gated calcium channels have been defined based on electrophysiological and pharmacological properties. * L-type, or dihydropyridinesensitive, calcium channels mediate long-lasting calcium currents and are most abundant in skeletal muscle where they are localized to the transverse tubule membrane. This tissue contains 50-to 100-fold more dihydropyridine receptor sites than other tissues and hence has been the principal tissue for molecular studies of the L-type channel. The most abundant form of the rabbit skeletal muscle L-type calcium channel is a complex of 5 subunits (reviewed in refs. 2-5): a1 (175 kDa), a 2 (143 kDa), p (55 kDa), y (30 kDa), and 6 (24-27 kDa). The 01-, p-, and y-subunits have been isolated and are products of distinct genes.6-sProtein
A calcium channel mutation causing hypokalemic periodic paralysis
Human Molecular Genetics, 1994
The only calcium channel mutation reported to date Is a deletion In the gene for the DHP-receptor a1-subunit resulting In neonatal death in muscular dysgenesls mice (1). In humans, this gene maps to chromosome 1q31-32. An autosomal dominant muscle disease, hypokalemic periodic paralysis (HypoPP), has been mapped to the same region (2). Sequencing of cDNA of two patients revealed a G-to-A base exchange of nucleotide 1583 predicting a substitution of histldlne for arglnine 528 . This affects the outermost positive charge in the transmembrane segment IIS4 that Is considered to participate in voltage sensing. By restriction fragment analysis, the mutation was detected in the affected members of 9 out of 25 HypoPP families. The results indicate that the DHP-receptor a1-subunit mutation causes HypoPP. An altered excitation -contraction coupling may explain the occurrence of muscle weakness.
Journal of Membrane Biology, 1999
The effects of a long-term blockade of L-type Ca2+ channels on membrane currents and on the number of dihydropyridine binding sites were investigated in skeletal muscle fibers. Ca2+ currents (I Ca) and intramembrane charge movement were monitored using a voltage-clamp technique. The peak amplitude of I Ca increased by more than 40% in fibers that were previously incubated for 24 hr in solutions containing the organic Ca2+ channel blocker nifedipine or in Ca2+-free conditions. A similar incubation period with Cd2+, an inorganic blocker, produced a moderate increase of 20% in peak I Ca. The maximum mobilized charge (Q max) increased by 50% in fibers preincubated in Ca2+-free solutions or in the presence of Cd2+. Microsomal preparations from frog skeletal muscle were isolated by differential centrifugation. Preincubation with Cd2+ prior to the isolation of the microsomal fraction doubled the number of 3H-PN200-110 binding sites and produced a similar increase in the values of the dissociation constant. The increase in the number of binding sites is consistent with the increase in the peak amplitude of I Ca as well as with the increase in Q max.
Different types of Ca2+ channels in mammalian skeletal muscle cells in culture
Proceedings of the National Academy of Sciences, 1986
This paper describes the existence of two pharmacologically distinct types of Ca2+ channels in rat skeletal muscle cells (myoballs) in culture. The first class of Ca2+ channels is insensitive to the dihydropyridine (DHP) (+)-PN 200-110; the second class of Ca2+ channels is blocked by low concentrations of (+)-PN 200-110. The two pharmacologically different Ca2+ channels are also different in their voltage and time dependence. The threshold for activation of the DHP-insensitive Ca2+ channel is near -65 mV, whereas the threshold for activation of the DHP-sensitive Ca2+ channel is near -30 mV. Current flowing through the DHP-insensitive Ca2+ channel is transient with relatively fast kinetics. Halfmaximal inactivation for the DHP-insensitive Ca2+ channel is observed at a holding potential Vho.5 = -78 mV and the channel is completely inactivated at -60 mV. Two different behaviors have been found for DHP-sensitive channels with two different kinetics of inactivation (one being about 16 times faster than the other at -2 mV) and two different voltage dependencies. These two different behaviors are often observed in the same myoball and may correspond to two different subtypes of DHP-sensitive Ca'+ channels or to two different modes of expression of one single Ca2+ channel protein.
Journal of Biological …, 2005
Auxiliary channel subunits regulate membrane expression and modulate current properties of voltageactivated Ca 2؉ channels and thus are involved in numerous important cell functions, including muscle contraction. Whereas the importance of the ␣ 1S ,  1a , and ␥ Ca 2؉ channel subunits in skeletal muscle has been determined by using null-mutant mice, the role of the ␣ 2 ␦-1 subunit in skeletal muscle is still elusive. We addressed this question by small interfering RNA silencing of ␣ 2 ␦-1 in reconstituted dysgenic (␣ 1S-null) myotubes and in BC3H1 skeletal muscle cells. Immunofluorescence labeling of the ␣ 1S and ␣ 2 ␦-1 subunits and whole cell patch clamp recordings demonstrated that triad targeting and functional expression of the skeletal muscle Ca 2؉ channel were not compromised by the depletion of the ␣ 2 ␦-1 subunit. The amplitudes and voltage dependences of L-type Ca 2؉ currents and of the depolarization-induced Ca 2؉ transients were identical in control and in ␣ 2 ␦-1-depleted muscle cells. However, ␣ 2 ␦-1 depletion significantly accelerated the current kinetics, most likely by the conversion of slowly activating into fast activating Ca 2؉ channels. Reverse transcription-PCR analysis indicated that ␣ 2 ␦-1 is the exclusive isoform expressed in differentiated BC3H1 cells and that depletion of ␣ 2 ␦-1 was not compensated by the up-regulation of any other ␣ 2 ␦ isoform. Thus, in skeletal muscle the Ca 2؉ channel ␣ 2 ␦-1 subunit functions as a major determinant of the characteristic slow L-type Ca 2؉ current kinetics. However, this subunit is not essential for targeting of Ca 2؉ channels or for their primary physiological role in activating skeletal muscle excitation-contraction coupling. Voltage-activated Ca 2ϩ channels are important signaling proteins in many cellular processes including muscle contrac
Biochemical and Biophysical Research Communications, 1988
The L-type Ca2+ channel is blocked by 1,4-dihydropyridines (DHP), by phenylalkylamines, by diphenylbutylpiperidines or by benzolactams. We first show with mouse muscle cells in culture that all these L-type Ca2+ channel blockers block contraction. However, voltage-clamp analysis associated to contraction measurements also clearly show that Ca2+ influx through L-type Ca2+ channels is not required for contraction. Therefore, there is a need for a voltage-sensor which would be responsible for the excitation-contraction (E-C) coupling. We are showing here that the voltage-sensor involved in E-C coupling and the L-type Ca2+ channel have a similar pharmacology. Some of the blockers used are more active on the voltage sensor, others on the L-type Ca2+ channel.
Proceedings of the …, 1994
Skeletal muscle L-type Ca+ channels respond to trains ofbriefdepolarizations with a strong shift ofthe voltag dependence of e activation toward more negative membrane potentials and slowing of channel deactivation. Increased Ca2+ entry tig from this potentition of channel activity may Increase cotale force in response to tetanic simuli. This voltage-dependent Ca ca pote on requires phosphorylation by cAMP-dependent protein k e (PKA) at a rate that sgst that kinase and canl may be maintained in dose proximity through kin anchoring. A peptide derived from the conserved kinase-bindn domain of a PKA-anchoring protein (AKAP) prevents potntlation by endogenous PKA as effectivey as inhibition of PKA by a specifc peptide inhibitor or by in of ATP from the intracellular solution. In coutrst, a proline-substiuted mutant of AKAP peptide has no effect. Potentiation in the presence of 2 pM exogenous catalytic subunit of PKA is unafected, ting that kinase anchoring is specifically blocked by the AKAP peptide. No effects of these agents were observed on the level or voltage dnd e of basl Ca2+ h el aciity before pteniaton, that dose physical promi between the skeletal muscle Ca2 channel and PKA is critical for voltage-dependent potentiation of Ca2e chann activity but not for basal activity.
The Journal of neuroscience : the official journal of the Society for Neuroscience, 2000
Missense mutations of the human skeletal muscle voltage-gated Na channel (hSkM1) underlie a variety of diseases, including hyperkalemic periodic paralysis (HyperPP), paramyotonia congenita, and potassium-aggravated myotonia. Another disorder of sarcolemmal excitability, hypokalemic periodic paralysis (HypoPP), which is usually caused by missense mutations of the S4 voltage sensors of the L-type Ca channel, was associated recently in one family with a mutation in the outermost arginine of the IIS4 voltage sensor (R669H) of hSkM1 (Bulman et al., 1999). Intriguingly, an arginine-to-histidine mutation at the homologous position in the L-type Ca(2+) channel (R528H) is a common cause of HypoPP. We have studied the gating properties of the hSkM1-R669H mutant Na channel experimentally in human embryonic kidney cells and found that it has no significant effects on activation or fast inactivation but does cause an enhancement of slow inactivation. R669H channels exhibit an approximately 10 mV...
Activation of L-type calcium channel in twitch skeletal muscle fibres of the frog
The Journal of physiology, 1996
1. The activation of the L-type calcium current (ICa) was studied in normally polarized (-100 mV) cut skeletal muscle fibres of the frog with the double Vaseline-gap voltage-clamp technique. Both external and internal solutions were Ca2+ buffered. Solutions were made in order to minimize all but the Ca2+ current. 2. The voltage-dependent components of the time course of activation were determined by two procedures: fast and slow components were evaluated by multiexponential fitting to current traces elicited by long voltage pulses (5 s) after removing inactivation; fast components were also determined by short voltage pulses having different duration (0.5-70 ms). 3. The components of deactivation were evaluated after removing the charge-movement current from the total tail current by the difference between two short (50 and 70 ms) voltage pulses to 10 mV, moving the same intramembrane charge. Two exponential components, fast and slow (time constants, 6 +/- 0.3 and 90 +/- 7 ms at -10...