Effect of bay K 8644 (-) and the beta2a subunit on Ca2+-dependent inactivation in alpha1C Ca2+ channels.
Ca2+ currents recorded from Xenopus oocytes expressing only the alpha1C pore-forming subunit of the cardiac Ca2+ channel show Ca2+-dependent inactivation with a single exponential decay. This current-dependent inactivation is not detected for inward Ba2+ currents in external Ba2+. Facilitation of pore opening speeds up the Ca2+-dependent inactivation process and makes evident an initial fast rate of decay. Facilitation can be achieved by (a) coexpression of the beta2a subunit with the alpha1C subunit, or (b) addition of saturating Bay K 8644 (-) concentration to alpha1C channels. The addition of Bay K 8644 (-) to alpha1Cbeta2a channels makes both rates of inactivation faster. All these maneuvers do not induce inactivation in Ba2+ currents in our expression system. These results support the hypothesis of a mechanism for the Ca2+-dependent inactivation process that is sensitive to both Ca2+ flux (single channel amplitude) and open probability. We conclude that the Ca2+ site for inactivation is in the alpha1C pore-forming subunit and we propose a kinetic model to account for the main features of alpha1Cbeta2a Ca2+ currents.
Noceti
F
F
Department of Anesthesiology, School of Medicine, University of California, Los Angeles, Los Angeles, California 90095-1778, USA.
Olcese
R
R
Qin
N
N
Zhou
J
J
Stefani
E
E
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology*; D000818:Animals; D002120:Calcium Channel Agonists / Q000494:pharmacology*; D015220:Calcium Channels / Q000187:drug effects / Q000502:physiology*; D018076:DNA, Complementary; D004558:Electric Stimulation; D004594:Electrophysiology; D006321:Heart / Q000502:physiology; D066298:In Vitro Techniques; D007700:Kinetics; D008958:Models, Molecular; D009865:Oocytes; D014982:Xenopus laevis
D002120:Calcium Channel Agonists; D015220:Calcium Channels; D018076:DNA, Complementary; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester