The vascular diameter of the gerbilline spiral modiolar artery has been shown to depend on the presence of extracellular Ca2+ but it remained unknown whether the smooth muscle cells of this arteriole contain a Ca2+ sensing receptor (CaSR). The cytosolic Ca2+ concentration ([Ca2+] 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 Ca2+ concentration ([Ca2+] o ) from 1 to 10 mm caused a biphasic increase in [Ca2+] i that was paralleled by a vasoconstriction. The initial rate of this vasoconstriction, 2.01 ± 0.07 μm/sec (n= 131), was inhibited when cytosolic Ca2+ stores were presumably depleted with thapsigargin (IC 50= 3 × 10−9 m, n= 26) or ryanodine (IC 50= 4 × 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 Ca2+ 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 Ca2+ channel blocker 10−6 Gd3+ (n= 6) or the Na+/Ca2+ exchanger blocker 10−4 m Ni2+ (n= 5). The agonist rank potency order was Gd3+ > Ni2+ > Ca2+ >> neomycin = Mg2+. 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.
The Journal of Membrane Biology – Springer Journals
Published: Jun 1, 2000
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