AJP - Cell Physiology, Vol 271, Issue 3 C842-C850, Copyright © 1996 by American Physiological Society

ARTICLES

High permeation of L-type Ca2+ channels at physiological [Ca2+]: homogeneity and dependence on the alpha 1-subunit

M. Gollasch, C. Ried, M. Liebold, H. Haller, F. Hofmann and F. C. Luft
Franz Volhard Clinic, Virchow Klinikum, Humboldt University of Berlin, Germany.

Molecular cloning has identified multiple isoforms of dihydropyridine-sensitive C-class L-type Ca2+ channels. We tested the hypotheses that L-type (C-class) channels exhibit homogeneous high permeation properties at physiological Ca2+ concentrations and membrane potentials. We measured unitary currents through single dihydropyridine-sensitive omega-conotoxin-insensitive endocrine and smooth muscle L-type Ca2+ channels in rat pituitary GH3 and rat aortic A7r5 cell lines. We also measured unitary currents through smooth muscle (Cb) Ca2+ channel alpha 1-subunits in Chinese hamster ovary (CHO) cells. Our results show that single channel conductances of all three L-type (C-class) channels are uniform with high Ba2+ concentrations, e.g., approximately 23 pS with 110 mM Ba2+. The single channel conductances were reduced to similar values when the Ba2+ concentration was lowered to near-physiological values: 11.1, 9.3, and 8.4 pS in GH3, A7r5, and CHO cells at 2 mM Ba2+, respectively. The single channel conductances were not significantly different with near-physiological Ca2+ concentrations: 5.5, 5.9, and 4.9 pS in GH3, A7r5, and CHO cells at 2 mM Ca2+, respectively. The data suggest that L-type (C-class) channels are homogeneous in terms of Ca2+ permeation at physiological charge carrier concentrations and membrane potentials. Furthermore, the data indicate that the relatively high Ca2+ permeation under physiological conditions is determined by the intrinsic properties of the pore-forming Ca2+ channel alpha 1-subunit.

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