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Department of Cell and Molecular Physiology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7545
This study provides
new information about the relative importance of calcium mobilization
and entry in the renal vascular response to adrenoceptor activation in
afferent arterioles isolated from 7- to 8-wk-old Wistar-Kyoto (WKY) and
spontaneously hypertensive rats (SHR). Intracellular free calcium
concentration ([Ca2+]i) was measured in
microdissected arterioles utilizing ratiometric photometry of fura 2 fluorescence. There was no significant strain difference in baseline
[Ca2+]i. Norepinephrine (NE;
10
6 and 10
7 M) elicited immediate,
sustained increases in [Ca2+]i. The general
temporal pattern of response to 10
6 M NE consisted of an
initial peak and a maintained plateau phase. The response to NE was
partially blocked by nifedipine (10
6 M) or
8-(N,N-diethylamino) octyl-3,4,5-trimetoxybenzoate (TMB-8; 10
5 M). A calcium-free external solution abolished the
sustained [Ca2+]i plateau response to NE,
with less influence on the peak response. In the absence of calcium
entry, TMB-8 (10
5 M) completely blocked the calcium
response to NE in WKY but not SHR, suggesting strain differences in
mobilization. A higher concentration of TMB-8 (10
4 M),
however, blocked all discernible mobilization in both strains. We
conclude that there are differences in Ca2+ handling in
renal resistance vessels between young WKY and SHR with respect to
mobilization stimulated by
-adrenoceptors. Afferent arterioles of
young SHR appear to have a larger
inositol-1,4,5-trisphosphate-sensitive pool or release from a site less
accessible to TMB-8.
spontaneously hypertensive rats; Wistar-Kyoto rats; norepinephrine; hypertension; 8-(N,N-diethylamino) octyl-3,4,5-trimetoxybenzoate; nifedipine; vascular smooth muscle; inositol-1,4,5-trisphosphate-mediated mobilization; L-type calcium channel; renal circulation
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