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Division of Nephrology, University of Maryland School of Medicine, Baltimore, Maryland 21201-1595; and Division of Nephrology, Milton S. Hershey Medical Center, Pennsylvania State University, Hershey, Pennsylvania 17033
Outer medullary descending vasa recta
(OMDVR) were dissected from the outer medullary vascular bundles of
young rats, perfused in vitro, and loaded with fura 2 for
measurement of intracellular calcium concentration
([Ca2+]i)
by fluorescent ratio imaging. Fluorescent video images revealed that
fura 2 selectively loads into endothelial cells but not pericytes. Bradykinin (BK), at concentrations
>10
11 M, elicited an
increase in
[Ca2+]i
from baseline values in the range from 50 to 100 nM to peak values of
600-800 nM followed by a sustained plateau of 150-250 nM. The vasopressin
V1-receptor agonist
[Phe2,Ile3,Orn8]vasopressin
constricted OMDVR but yielded no observable
[Ca2+]i
response, a finding that is consistent with an endothelial cell origin
for the fura 2 fluorescent signal. The BK
[Ca2+]i
response was blocked by the selective BK
B2-receptor antagonists D-Arg-[Hyp3,Thi5,8, D-Phe7]BK
and
D-Arg-[Hyp3,D-Phe7,Leu8]BK
but not the B1 antagonist
des-Arg9-[Leu8]BK.
BK vasodilated microperfused OMDVR that had been preconstricted with
108 M angiotensin II. We
conclude that the
[Ca2+]i
response of OMDVR endothelia can be selectively studied with fura 2, that BK increases endothelial
[Ca2+]i
via the B2 receptor, and that BK
can vasodilate descending vasa recta.
microcirculation; microperfusion; renal medulla; receptor; calcium
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