Gating of the HypoPP-1 mutations: I. Mutant-specific effects and cooperativity.
Hypokalemic periodic paralysis type 1 (HypoPP-1) is a hereditary muscular disorder caused by point mutations in the gene encoding the voltage-gated Ca(2+) channel alpha subunit (Ca(v)1.1). Despite extensive research, the results on HypoPP-1 mutations are minor and controversial, as it is difficult to analyse Ca(2+) channel activation macroscopically due to an existence of two open states. In this study, we heterologously expressed the wild-type and HypoPP-1 mutations introduced into the rabbit cardiac Ca(2+) channel (R650H, R1362H, R1362G) in HEK-293 cells. To examine the cooperative effects of the mutations on channel gating, we expressed two double mutants (R650H/R1362H, R650H/R1362G). We performed whole-cell patch-clamp and, to obtain more information, applied a global fitting procedure whereby several current traces elicited by different potentials were simultaneously fit to the kinetic model containing four closed, two open and two inactivated states. We found that all HypoPP-1 mutations have "loss-of-function" features: D4/S4 mutations shift the equilibrium to the closed states, which results in reduced open probability, shorter openings and, therefore, in smaller currents, and the D2/S4 mutant slows the activation. In addition, HypoPP-1 histidine mutants favored the second open state O(2) with a possibly lower channel selectivity. Cooperativity between the D2/S4 and D4/S4 HypoPP-1 mutations manifested in dominant effects of the D4/S4 mutations on kinetics of the double mutants, suggesting different roles of D2/S4 and D4/S4 voltage sensors in the gating of voltage-gated calcium channels.
Kuzmenkin
Alexey
A
Department of Applied Physiology, University of Ulm, 89081, Ulm, Germany. alexei21@hotmail.com
Hang
Chao
C
Kuzmenkina
Elza
E
Jurkat-Rott
Karin
K
D019943:Amino Acid Substitution; D000818:Animals; D020746:Calcium Channels, L-Type / Q000235:genetics* / Q000378:metabolism*; D002460:Cell Line; D006801:Humans; D020514:Hypokalemic Periodic Paralysis / Q000235:genetics* / Q000378:metabolism*; D066298:In Vitro Techniques; D015640:Ion Channel Gating; D007700:Kinetics; D008564:Membrane Potentials; D008954:Models, Biological; D016297:Mutagenesis, Site-Directed; D017354:Point Mutation; D011817:Rabbits; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism
D020746:Calcium Channels, L-Type; D011994:Recombinant Proteins