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Division of Nephrology, University of Maryland School of Medicine, Baltimore, Maryland 21201-1595
We tested the hypothesis that constriction
of descending vasa recta (DVR) is mediated by voltage-gated calcium
entry. K+ channel blockade with BaCl2 (1 mM) or
TEACl (30 mM) depolarized DVR smooth muscle/pericytes and constricted
in vitro-perfused vessels. Pericyte depolarization by 100 mM
extracellular KCl constricted DVR and increased pericyte intracellular
Ca2+ ([Ca2+]i). The
KATP channel opener pinacidil
(10
7-10
4 M) hyperpolarized resting
pericytes, repolarized pericytes previously depolarized by ANG II
(10
8 M), and vasodilated DVR. The DVR vasodilator
bradykinin (10
7 M) also reversed ANG II depolarization.
The L-type Ca2+ channel blocker diltiazem vasodilated ANG
II (10
8 M)- or KCl (100 mM)-preconstricted DVR, and the
L-type agonist BayK 8644 constricted DVR. The plateau phase of the
pericyte [Ca2+]i response to ANG II was
inhibited by diltiazem. These data support the conclusion that DVR
vasoreactivity is controlled through variation of membrane potential
and voltage-gated Ca2+ entry into the pericyte cytoplasm.
medulla; kidney; microcirculation; patch clamp; fura-2; KCl
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