Evidence for capacitative and non-capacitative Ca 2+ entry pathways coexist in A10 vascular smooth muscle cells

Abstract

It is generally thought that receptor-operated Ca 2+ entry is related to store-operated or capacitative Ca 2+ entry mechanism. Recent evidence suggests that non-capacitative Ca 2+ entry pathways are also involved in receptor activated Ca 2+ influx in many different kinds of cells. In this study, we studied whether α 1-adrenoreceptor (α 1-AR)-activated Ca 2+ entry is coupled to both capacitative and non-capacitative pathways in A10 vascular smooth muscle cells by fura-2 fluorescence probe and conventional whole-cell patch clamp techniques. We found that both thapsigargin (TG) and phenylephrine (Phe) induced transient increase in cytoplasmic Ca 2+ concentration ([Ca 2+] i) in Ca 2+-free medium, and subsequent addition of Ca 2+ evoked a sustained [Ca 2+] i rise. When the membrane potential was held at − 60 mV, both TG and Phe activated inward currents, which were inhibited by GdCl 3(Gd 3+), 0Na +/0Ca 2+ solution and 1-{β[3-(4-mehtoxyphenyl)propoxy]-4-methoxypheneth-yl}-1H- imidazole hydro-chloride (SK&F96365), but not by nifedipine. When Ca 2+ store was depleted by TG in Ca 2+-free solution, Phe failed to further evoke [Ca 2+] i rise. However, when capacitative Ca 2+ entry was activated by TG in the medium containing Ca 2+, 10 μM Phe further increased [Ca 2+] i. At the same concentration, TG activated an inward cation current, subsequent addition of Phe also further induced an inward cation current. Furthermore, the amplitudes of [Ca 2+] i increase and current density induced by Phe in the presence of TG were less than that induced by Phe alone. Our results suggest that both capacitative and non-capacitative Ca 2+ entry pathways are involved in Ca 2+ influx induced by activation of α 1-AR in A10 vascular smooth muscle cells.