Calcium-dependent inactivation of the dihydropyridine-sensitive calcium channels in GH3 cells

• Type of Material: Article
• Authors: Daniel Kalman, Emory University; P.H. Olague, University of California, Los Angeles; C. Erxleben, University of California, Los Angeles; D.L. Armstrong, University of California, Los Angeles
• Language: English
• Date: 1988-10-01
• Publisher: Rockefeller University Press
• Publication Version: Final Published Version
• Copyright Statement: © 1988 Rockefeller University Press
• License: Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported
• Final Published Version (URL): http://dx.doi.org/10.1085/jgp.92.4.531
• Title of Journal or Parent Work: Journal of General Physiology
• ISSN: 0022-1295
• Volume: 92
• Issue: 4
• Start Page: 531
• End Page: 548
• Keywords: PHYSIOLOGY; Science & Technology; Life Sciences & Biomedicine; Physiology
• Research Categories: Biology, General; Health Sciences, Pathology; Health Sciences, General

Abstract

The inactivation of calcium channels in mammalian pituitary tumor cells (GH3) was studied patch electrodes under voltage clamp in cell-free membrane patches and dialyzed cells. The calcium current elicited by depolarization from a holding potential -40 mV predominantly through one class of channels previously shown to be modulated by dihydropyridines and cAMP-dependent phosphorylation (Armstrong and Eckert, 1987). When exogenous calcium buffers were omitted from the pipette solution, the macroscopic calcium current through those channels inactivated with a half time of ~10 ms to a steady state level 40-75% smaller than the peak. Inactivation was also measured as the reduction in peak current during a test pulse that closely followed a prepulse. Inactivation was largely reduced or eliminated by (a) buffering free calcium in the pipette solution to < 10-8 M; (b) replacing extracellular calcium with barium; (c) increasing the prepulse voltage from +10 to +60 mV; or (d) increasing the intracellular concentration of cAMP, either 'directly' with dibutyryl-cAMP or indirectly by activating adenylate cyclase with forskolin or vasoactive intestinal peptide. Thus, inactivation of the dihydropyridine-sensitive calcium channels in GH3 cells only occurs when membrane depolarization leads to calcium ion entry and intracellular accumulation.