The vascular diameter of the gerbilline spiral modiolar artery has been shown to depend on the presence of extracellular Ca(2+) but it remained unknown whether the smooth muscle cells of this arteriole contain a Ca(2+) sensing receptor (CaSR). The cytosolic Ca(2+) concentration ([Ca(2+)](i)) was monitored as fluo 3 fluorescence and the vascular diameter was measured by video-microscopy in isolated in vitro superfused spiral modiolar arteries. RT-PCR was used to probe for the presence of CaSR transcripts. Increasing the extracellular Ca(2+) concentration ([Ca(2+)](o)) from 1 to 10 mm caused a biphasic increase in [Ca(2+)](i) that was paralleled by a vasoconstriction. The initial rate of this vasoconstriction, 2.01 +/- 0.07 microm/sec (n = 131), was inhibited when cytosolic Ca(2+) stores were presumably depleted with thapsigargin (IC(50) = 3 x 10(-9) m, n = 26) or ryanodine (IC(50) = 4 x 10(-8) m, n = 25) or when PLC was inhibited by 10(-6) m U73122 (n = 8). The initial rate of this constriction was not affected by the L-type Ca(2+) channel blocker 10(-6) m nifedipine (n = 5), by 10(-6) m U73343 (n = 6), which is the inactive analogue of U73122, by the T-type Ca(2+) channel blocker 10(-6) Gd(3+) (n = 6) or the Na(+)/Ca(2+) exchanger blocker 10(-4) m Ni(2+) (n = 5). The agonist rank potency order was Gd(3+) > Ni(2+) > Ca(2+) >> neomycin = Mg(2+). Analysis of RNA isolated from the SMA revealed a RT-PCR product of the appropriate size for the CaSR (448 bp). Sequence analysis of the amplified cDNA fragment revealed a 94-96% amino acid identity compared to other CaSRs. These results demonstrate that the spiral modiolar artery contains a CaSR, which is most likely located in the vascular smooth muscle cells.