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Department of Cell and Molecular Physiology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7545
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
cells (VSMC) derived from rat preglomerular vessels.
[Ca2+]i
was measured using fura-2 ratiometric fluorescence. Vasopressin V1
receptor agonist (V1R) (10
7
M) increased
[Ca2+]i
by ~100 nM. A calcium channel blocker (CCB), nifedipine or verapamil
(10
7 M), inhibited the
response by ~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 calcium-free buffer or when EGTA was
present. In nominally Ca2+-free
medium, the sarcoplasmic reticulum
Ca2+-ATPase inhibitors (SRCAI),
thapsigargin and cyclopiazonic acid (CPA), increased
[Ca2+]i
from 97 to 128 and 143 nM, respectively, and to 214 and 220 nM,
respectively, when 1 mM extracellular
Ca2+ was added. In the presence of
verapamil, the results with CPA acid 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+ (1 mM),
demonstrating divalent cation entry. These studies provide evidence for
capacitative (store- operated) calcium entry in VSMC freshly isolated
from rat preglomerular arterioles.
calcium signaling; store-operated calcium entry; vascular smooth muscle; renal hemodynamics; afferent arterioles; sarcoplasmic reticulum; calcium adenosinetriphosphatase; voltage-gated calcium channels
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