Impaired Gating of an L-Type Ca2+ Channel Carrying a Mutation Linked to Malignant Hyperthermia

Abstract

Recently, we characterized the functional properties of a mutant skeletal muscle L-type Ca(2+) channel (CaV1.1 R174W) linked to the pharmacogenetic disorder malignant hyperthermia. Although the R174W mutation neutralizes the innermost basic amino acid in the voltage-sensing S4 helix of the first conserved membrane repeat of CaV1.1, the ability of the mutant channel to engage excitation-contraction coupling was largely unaffected by the introduction of the bulky tryptophan residue. In stark contrast, the mutation ablated the ability of CaV1.1 to produce L-type current under our standard recording conditions. In this study, we have investigated the mechanism of channel dysfunction more extensively. We found that CaV1.1 R174W will open and conduct Ca(2+) in response to strong or prolonged depolarizations in the presence of the 1,4-dihydropyridine receptor agonist ±Bay K 8644. From these results, we have concluded that the R174W mutation impedes entry into both mode 1(low Po) and mode 2 (high Po) gating states and that these gating impairments can be partially overcome by maneuvers that promote entry into mode 2.

Channelopathies of Skeletal Muscle Excitability

“…Surprisingly, SR Ca 2+ release in response to depolarization was only mildly affected, and the largest changes were observed for L-type Ca 2+ currents. The R1086H channel had reduced P open (272), while T1345S had accelerated activation (184), and R174W had the most severe defect with no channel opening expect with strong prolonged depolarization or in the presence of agonists (11). …”

Bridging the myoplasmic gap II: more recent advances in skeletal muscle excitation–contraction coupling

“…Interestingly, the R174W mutation wiped out L-type Ca 2+ current by a distinctly different mechanism from the E1014K swap. As the R174W channel could be opened by a combination of pharmacological (Bay K 8644) and electrophysiological (long/strong depolarization) manipulations, it was posited that the mutation caused a profound depolarizing shift in channel activation that stabilized the closed state of the channel (Bannister and Beam, 2013b). A speculative explanation for the inability of R174W to achieve transitions required for the open confirmation without Bay K 8644 and long/strong depolarization was that the passage of the voltage sensor through the field of the plasma membrane is impeded by the bulky tryptophan residue.…”

A Review of Genetic and Physiological Disease Mechanisms Associated With Cav1 Channels: Implications for Incomplete Congenital Stationary Night Blindness Treatment

“…(B) Three functionally characterized hypermorphs in S6 repeats I and II of Cav1.4 [p.Gly369Asp ( Hoda et al, 2005 ), p.Phe753Cys ( Hope et al, 2005 ), p.Ile756Thr ( Peloquin et al, 2007 )] (red) are present at the equivalent position in Cav1.2: p.Gly402Ser ( Splawski et al, 2005 ) (equivalent to p.Gly369Asp) (blue) and Cav1.3: p.Gly403Asp/Arg ( Scholl et al, 2013 ) (equivalent to p.Gly369Asp), p.Ile750Met ( Scholl et al, 2013 ) (equivalent to p.Ile756Thr), p.Phe747Leu ( Pinggera et al, 2018 ) (equivalent to p.Phe753Cys) (green). (C) Five mutations to the VSDs (four hypomorphs and one null) are functionally analyzed mutants that damage the sensor’s voltage sensitivity and reduce the channel’s conductance in Cav1.1 [p.Arg174Trp ( Bannister and Beam, 2013 ), p.Arg528His ( Morrill et al, 1998 ), p.Arg1239His/Gly ( Morrill and Cannon, 1999 )] (purple), Cav1.3 [p.Arg990His ( Monteleone et al, 2017 )] (green), and Cav1.4 [p.Gly1007Arg ( Peloquin et al, 2007 )] (red). The conservation in paralogs is shown for each residue.…”