Renal arteriolar na+:ca2+ exchange in salt sensitive
hypertension.
Nelson, Lawrence D., M. Tino Unlap, James L. Lewis, and P. Darwin
Bell.
Departments of Medicine and Physiology & Nephrology Research and
Training Center, University of Alabama at Birmingham, Birmingham, AL
35294
APStracts 5:0215F, 1998.
The present studies were performed to assess Na+:Ca2+ exchange
activity in afferent and efferent arterioles from Dahl/Rapp salt
resistant (R) and salt sensitive (S) rats. Renal arterioles were
obtained by microdissection from S and R rats on either a low (0.3%
NaCl) or high (8.0% NaCl) salt diet. On the high salt diet, S rats
become markedly hypertensive. Cytosolic calcium concentration
([Ca2+]i) was measured in fura 2 loaded arterioles bathed in a
Ringer's solution in which Na (Nae) was varied from 150 to 2 mM (Na
was replaced with n-methyl-D-glucamine). Baseline [Ca2+]i was similar
in afferent arterioles of R and S rats fed low and high salt diet.
The change in [Ca2+]i (D[Ca2+]i) during reduction in Nae from 150 to
2 mM was 80 +/- 10 nM and 61 +/- 3 nM (NS) in afferent arterioles
from R rats fed the low and high salt diet, respectively. In afferent
arterioles from S rats on a high salt diet, D[Ca2+]i during
reductions in Nae from 150 to 2 mM, was attenuated (39 +/- 4 nM)
relative to the D[Ca2+]i of 79 +/- 13 nM (p < 0.05) obtained in
afferent arterioles from S rats on a low salt diet. In efferent
arterioles, baseline [Ca2+]i was similar in R and S rats fed low and
high salt diets, and D[Ca2+]i in response to reduction in Nae was
also not different in efferent arterioles from R and S rats fed low
or high salt diets. Differences in regulation of the exchanger in
afferent arterioles of S and R rats were assessed by determining the
effects of PKC activation by PMA (100 nM) on D[Ca2+]i in response to
reductions in Nae from 150 to 2 mM. PMA increased D[Ca2+]i in
afferent arterioles from R rats but not from S rats. These results
suggest that Na+:Ca2+ exchange activity is suppressed in afferent
arterioles of S rats that are on a high salt diet. In addition, there
appears to be a defect in the PKC-Na+:Ca2+ exchange pathway which
might contribute to altered [Ca2+]i regulation in this important
renal vascular segment in salt sensitive hypertension.
Received 18 September 1998; accepted in final form 10 December
1998.
APS Manuscript Number F304-7.
Article publication pending Am. J. Physiol. (Renal Physiology).
ISSN 1080-4757 Copyright 1998 The American Physiological Society.
Published in APStracts on 18 December 1998