Calcium-dependent inactivation of L-type calcium channels in planar lipid bilayers.
Intracellular Ca2+ can inhibit the activity of voltage-gated Ca channels by modulating the rate of channel inactivation. Ca(2+)-dependent inactivation of these channels may be a common negative feedback process important for regulating Ca2+ entry under physiological and pathological conditions. This article demonstrates that the inactivation of cardiac L-type Ca channels, reconstituted into planar lipid bilayers and studied in the presence of a dihydropyridine agonist, is sensitive to Ca2+. The rates and extents of inactivation, determined from ensemble averages of unitary Ba2+ currents, decreased when the calcium concentration facing the intracellular surface of the channel ([Ca2+]i) was lowered from approximately 10 microM to 20 nM by the addition of Ca2+ chelators. The rates and extents of Ba2+ current inactivation could also be increased by subsequent addition of Ca2+ raising the [Ca2+]i to 15 microM, thus demonstrating that the Ca2+ dependence of inactivation could be reversibly regulated by changes in [Ca2+]i. In addition, reconstituted Ca channels inactivated more quickly when the inward current was carried by Ca2+ than when it was carried by Ba2+, suggesting that local increases in [Ca2+]i could activate Ca(2+)-dependent inactivation. These data support models in which Ca2+ binds to the channel itself or to closely associated regulatory proteins to control the rate of channel inactivation, and are inconsistent with purely enzymatic models for channel inactivation.
Department of Pharmacology and Physiology, University of North Carolina at Chapel Hill 27599.
J A
JA
Haack
R L
RL
Rosenberg
D000818:Animals; D001464:Barium / Q000494:pharmacology; D055592:Biophysical Phenomena; D001703:Biophysics; D002118:Calcium / Q000494:pharmacology*; D002121:Calcium Channel Blockers; D005246:Feedback; D066298:In Vitro Techniques; D007700:Kinetics; D008051:Lipid Bilayers / Q000378:metabolism*; D009206:Myocardium / Q000378:metabolism; D010539:Permeability; D012508:Sarcolemma / Q000378:metabolism; D013552:Swine
D002121:Calcium Channel Blockers; D008051:Lipid Bilayers; D001464:Barium; D002118:Calcium