AFLUID October 46/4

Fellner, Susan K., and William J. Arendshorst. Capacitative calcium entry in smooth muscle cells from preglomerular vessels. Am. J. Physiol. 277 (Renal Physiol. 46): F533– F542, 1999.—Calcium entry via voltage-gated L-type channels is responsible for at least half of the increase in cytosolic calcium ([Ca]i) in afferent arterioles following agonist stimulation. We sought the presence of capacitative calcium entry in fresh vascular smooth muscle cells (VSMC) derived from rat preglomerular vessels. [Ca]i was measured using fura-2 ratiometric fluorescence. Vasopressin V1 receptor agonist (V1R) (1027 M) increased [Ca]i by ,100 nM. A calcium channel blocker (CCB), nifedipine or verapamil (1027 M), inhibited the response by ,50%. V1R in the presence of CCB increased [Ca]i from 106 to 176 nM, confirming that calcium mobilization and/or entry may occur independent of voltagegated channels. In nominally Ca21-free buffer, V1R increased [Ca]i from 94 to 129 nM, denoting mobilization; addition of CaCl2 (1 mM) further elevated [Ca]i to 176 nM, indicating a secondary phase of Ca21 entry. Similar responses were obtained when CCB was present in calcium-free buffer or when EGTA was present. In nominally Ca21-free medium, the sarcoplasmic reticulum Ca21-ATPase inhibitors (SRCAI), thapsigargin and cyclopiazonic acid (CPA), increased [Ca]i from 97 to 128 and 143 nM, respectively, and to 214 and 220 nM, respectively, when 1 mM extracellular Ca21 was added. In the presence of verapamil, the results with CPA acid were nearly identical. In Ca21-free buffer, the stimulatory effect of V1R or SRCAI on the Ca21/fura signal was quenched by the addition of Mn21 (1 mM), demonstrating divalent cation entry. These studies provide evidence for capacitative (storeoperated) calcium entry in VSMC freshly isolated from rat preglomerular arterioles.