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-salt (0.3% NaCl) or high-salt (8.0% NaCl) 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 solution in which extracellular Na (Na_e) 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 ([Ca²⁺]_i) during reduction in Na_e from 150 to 2 mM was 80 ± 10 and 61 ± 3 nM (not significant) 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, [Ca²⁺]_i during reductions in Na_e from 150 to 2 mM was attenuated (39 ± 4 nM) relative to the [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 [Ca²⁺]_i in response to reduction in Na_e 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 protein kinase C (PKC) activation by phorbol 12-myristate 13-acetate (PMA, 100 nM) on [Ca²⁺]_i in response to reductions in Na_e from 150 to 2 mM. PMA increased [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 that might contribute to altered [Ca²⁺]_i regulation in this important renal vascular segment in salt-sensitive hypertension.

sodium/calcium exchange; protein kinase C; renal afferent and efferent arterioles

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