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Publication : Voltage-dependent Ca(2+) release is impaired in hypokalemic periodic paralysis caused by Ca(V)1.1-R528H but not by Na(V)1.4-R669H.

First Author  DiFranco M Year  2022
Journal  Am J Physiol Cell Physiol Volume  323
Issue  2 Pages  C478-C485
PubMed ID  35759432 Mgi Jnum  J:330864
Mgi Id  MGI:7344398 Doi  10.1152/ajpcell.00209.2022
Citation  DiFranco M, et al. (2022) Voltage-dependent Ca(2+) release is impaired in hypokalemic periodic paralysis caused by CaV1.1-R528H but not by NaV1.4-R669H. Am J Physiol Cell Physiol 323(2):C478-C485
abstractText  Hypokalemic periodic paralysis (HypoPP) is a channelopathy of skeletal muscle caused by missense mutations in the voltage sensor domains (usually at an arginine of the S4 segment) of the CaV1.1 calcium channel or of the NaV1.4 sodium channel. The primary clinical manifestation is recurrent attacks of weakness, resulting from impaired excitability of anomalously depolarized fibers containing leaky mutant channels. Although the ictal loss of fiber excitability is sufficient to explain the acute episodes of weakness, a deleterious change in voltage sensor function for CaV1.1 mutant channels may also compromise excitation-contraction coupling (EC-coupling). We used the low-affinity Ca(2+) indicator Oregon Green 488 BAPTA-5N (OGB-5N) to assess voltage-dependent Ca(2+)-release as a measure of EC-coupling for our knock-in mutant mouse models of HypoPP. The peak DeltaF/F0 in fibers isolated from CaV1.1-R528H mice was about two-thirds of the amplitude observed in WT mice; whereas in HypoPP fibers from NaV1.4-R669H mice the DeltaF/F0 was indistinguishable from WT. No difference in the voltage dependence of DeltaF/F0 from WT was observed for fibers from either HypoPP mouse model. Because late-onset permanent muscle weakness is more severe for CaV1.1-associated HypoPP than for NaV1.4, we propose that the reduced Ca(2+)-release for CaV1.1-R528H mutant channels may increase the susceptibility to fixed myopathic weakness. In contrast, the episodes of transient weakness are similar for CaV1.1- and NaV1.4-associated HypoPP, consistent with the notion that acute attacks of weakness are primarily caused by leaky channels and are not a consequence of reduced Ca(2+)-release.
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