Calcium currents in the A7r5 smooth muscle-derived cell line: Calcium-dependent and voltage-dependent inactivation

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Abstract

Inactivation of a dihydropyridine-sensitive calcium current was studied in a cell line (A7r5) derived from smooth muscle of the rat thoracic aorta. Inactivation is faster with extracellular Ca2+ than with Ba2+. In Ba2+, inactivation increases monotonically with depolarization. In Ca2+, inactivation is related to the amount of inward current, so that little inactivation is seen in Ca2+ for brief depolarizations approaching the reversal potential. Longer depolarizations in Ca2+ reveal two components of inactivation, the slower component behaving like that observed in Ba2+. Furthermore, lowering extracellular Ca2+ slows inactivation. These results are consistent with the coexistence of two inactivation processes, a slow voltage-dependent inactivation, and a more rapid current-dependent inactivation which is observable only with Ca2+. Ca2+-dependent inactivation is decreased but not eliminated when intracellular Ca2+ is buffered by 10 mM BAPTA, suggesting that Ca2+ acts at a site on or near the channel. We also studied recovery from inactivation after either a short pulse (able to produce significant inactivation only in Ca2+) or a long pulse (giving similar inactivation with either cation). Surprisingly, recovery from Ca2+-dependent inactivation was voltage dependent. This suggests that the pathways for recovery from inactivation are similar regardless of how inactivation is generated. We propose a model where Ca2+- and voltage-dependent inactivation occur independently.

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Giannattasio, B., Jones, S. W., & Scarpa, A. (1991). Calcium currents in the A7r5 smooth muscle-derived cell line: Calcium-dependent and voltage-dependent inactivation. Journal of General Physiology, 98(5), 987–1003. https://doi.org/10.1085/jgp.98.5.987

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