Chloride-dependent calcium transients induced by angiotensin II in vascular smooth muscle cells

Abstract

Cl–is essential for the vasoconstrictive response to angiotensin II (ANG II). In vascular smooth muscle cells (VSMC), we determined whether ANG II-induced transient increase in intracellular Ca2+concentration ([Ca2+]i) is Cl–dependent. After incubating the cells at different extracellular Cl–concentration ([Cl–]e) for 40 min, the ANG II-induced Ca2+transients at 120 meq/l Cl–were more than twice those at either 80 or 20 meq/l Cl–. Replacing Cl–with bicarbonate or gluconate yielded similar results. In addition, after removal of extracellular Ca2+, ANG II-induced as well as platelet-derived growth factor-induced Ca2+release exhibited Cl–dependency. The difference of Ca2+release with high vs. low [Cl–]ewas not affected by acutely altering [Cl–]e1 min before administration of ANG II when [Cl–]iwas yet to be equilibrated with [Cl–]e. Pretreatment of a Cl–channel inhibitor, 5-nitro-2-(3-phenylpropylamino)benzoic acid, increased ANG II-induced Ca2+release and entry at 20 meq/l Cl–but did not alter those at 120 meq/l Cl–. However, after equilibration, a reduced [Cl–]edid not affect thapsigargin-induced Ca2+release, suggesting that Cl–may not affect the size of intracellular Ca2+stores. Nevertheless, at high [Cl–], the peak increase of inositol 1,4,5-trisphosphate [Ins(1,4,5)P3] induced by ANG II was approximately sixfold that at low [Cl–]. Thus the Cl–-dependent effects of ANG II on Ca2+transients may be mediated, at least in part, by a Cl–-dependent Ins(1,4,5)P3accumulation in VSMC.