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Division of Nephrology, University of Maryland School of Medicine, Baltimore 21201-1595; and Department of Biology, Towson University, Towson, Maryland 21252
We tested whether the respective
angiotensin type 1 (AT1) and 2 (AT2) receptor
subtype antagonists losartan and PD-123319 could block the descending
vasa recta (DVR) endothelial intracellular calcium concentration
([Ca2+]i) suppression induced by ANG II. ANG
II partially reversed the increase in [Ca2+]i
generated by cyclopiazonic acid (CPA; 10
5 M),
acetylcholine (ACh; 10
5 M), or bradykinin (BK;
10
7 M). Losartan (10
5 M) blocked that
effect. When vessels were treated with ANG II before stimulation with
BK and ACh, concomitant AT2 receptor blockade with
PD-123319 (10
8 M) augmented the suppression of
endothelial [Ca2+]i responses. Similarly,
preactivation with the AT2 receptor agonist CGP-42112A
(10
8 M) prevented AT1 receptor stimulation
with ANG II + PD-123319 from suppressing endothelial
[Ca2+]i. In contrast to endothelial
[Ca2+]i suppression by ANG II, pericyte
[Ca2+]i exhibited typical peak and plateau
[Ca2+]i responses that were blocked by
losartan but not PD-123319. DVR vasoconstriction by ANG II was
augmented when AT2 receptors were blocked with PD-123319.
Similarly, AT2 receptor stimulation with CGP-42112A delayed
the onset of ANG II-induced constriction. PD-123319 alone
(10
5 M) showed no AT1-like action to
constrict microperfused DVR or increase pericyte
[Ca2+]i. We conclude that ANG II suppression
of endothelial [Ca2+]i and stimulation of
pericyte [Ca2+]i is mediated by
AT1 or AT1-like receptors. Furthermore,
AT2 receptor activation opposes ANG II-induced endothelial
[Ca2+]i suppression and abrogates ANG
II-induced DVR vasoconstriction.
kidney; vasoconstriction; vasodilation; medulla; blood flow
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