Gating of the HypoPP-1 mutations: II. Effects of a calcium-channel agonist BayK 8644.
L-type calcium-channel mutations causing hypokalemic periodic paralysis type 1 (HypoPP-1) have pronounced "loss-of-function" features and stabilize the less-selective second open state O(2), as we demonstrated in the companion paper. Here, we compared the effects of the L-type calcium-channel activator (+/-)BayK 8644 (BayK) on the heterologously expressed wild-type (WT) calcium channel, rabbit Cav1.2 HypoPP-1 analogs, and two double mutants (R650H/R1362H, R650H/R1362G). Our goal was to elucidate (1) whether the "loss-of-function" in HypoPP-1 can be compensated by BayK application, (2) how the less-selective open state is affected by BayK in WT and HypoPP-1 mutants, as well as (3) to gain an insight into BayK mechanism of action. Ionic currents were examined by whole-cell patch-clamp and analyzed by the global-fitting procedure. Our results imply that (1) BayK promotes channel activation, but equalized the differences among the WT and mutants, thus attenuating HypoPP-related effects on activation and deactivation; (2) BayK binds to the first open state O(1), and then serves as a catalyst for O(2) formation; (3) binding of BayK is impaired in the HypoPP mutants, thus affecting the formation of the less-selective second open state; (4) BayK affects cooperativity between the single HypoPP-1 mutations at all stages of the channel gating; and (5) BayK favoring of O(2) lowers calcium-channel selectivity.
Kuzmenkin
Alexey
A
Department of Applied Physiology, University of Ulm, 89069 Ulm, Germany.
Hang
Chao
C
Kuzmenkina
Elza
E
Jurkat-Rott
Karin
K
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology*; D002120:Calcium Channel Agonists / Q000494:pharmacology*; D020746:Calcium Channels, L-Type / Q000187:drug effects / Q000235:genetics* / Q000502:physiology; D002460:Cell Line; D006801:Humans; D020514:Hypokalemic Periodic Paralysis / Q000235:genetics* / Q000503:physiopathology; D015640:Ion Channel Gating / Q000187:drug effects* / Q000502:physiology; D010100:Oxygen / Q000378:metabolism; D018408:Patch-Clamp Techniques
D002120:Calcium Channel Agonists; D020746:Calcium Channels, L-Type; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D010100:Oxygen