Capacitative calcium entry in smooth muscle cells from
preglomerular vessels.
Fellner, Susan K., and William J. Arendshorst.
Department of Cell and Molecular Physiology, University of North
Carolina at Chapel Hill, Chapel Hill, NC 27599-7545
APStracts 6:0106F, 1999.
Calcium entry via voltage-gated L-type channels is responsible for at
least half of the increase in cytosolic calcium ([Ca2+]i) in afferent
arterioles following agonist stimulation. We sought the presence of
capacitative calcium entry in fresh vascular smooth muscle (VSMC)
cells derived from rat preglomerular vessels.. Cytosolic calcium
concentration was measured using fura-2 ratiometric fluorescence.
Vasopression_1 receptor agonist (V1R) (10-7M) increased [Ca2+]i by
about 100 nM. Calcium channel blockers (CCB) nifedipine or verapamil
(10-7M) inhibited the response by approximately 50%. V1R in the
presence of CCB increased [Ca2+]i from 106 to 176 nM confirming that
calcium mobilization and/or entry may occur independent of voltage
-gated channels. In nominally Ca2+-free buffer, V1R increased [Ca2+]i
from 94 to 129 nM, denoting mobilization; addition of CaCl2 (1 mM)
further elevated [Ca2+]i to 176 nM, indicating a secondary phase of
Ca2+ entry . Similar responses were obtained when CCB was present in
the calcium_free buffer or when EGTA was present. In nominally Ca2+
-free medium, the sarcoplasmic reticulum Ca 2+-ATPase inhibitors
(SRCAI) thapsigargin and cyclopiazonic acid, increased [Ca2+]i from
97 nM to 128 and 143 nM respectively, and to 214 and 220 nM when 1 mM
Ca2+ was added. In the presence of verapamil, the results with CPA
were nearly identical. In Ca2+-free buffer, the stimulatory effect of
V1R or SRCAI on the Ca2+/fura signal was quenched by the addition of
Mn2+ (1mM), demonstrating divalent cation entry. These studies
provide evidence for capacitative (store operated) calcium entry in
VSMC freshly isolated from rat preglomerular arterioles.
Received 16 November 1998; accepted in final form 21 May 1999.
APS Manuscript Number F300-8.
Article publication pending Am. J. Physiol. (Renal Physiology).
ISSN 1080-4757 Copyright 1999 The American Physiological Society.
Published in APStracts on 14 June 1999