Characterization of sodium-calcium exchange in rabbit renal arterioles

Experiments were performed to test the hypothesis that renal arterioles exhibit Na-Ca exchange capability and that this process is regulated by protein kinase C (PKC). Glomeruli with attached arterioles were dissected from rabbit kidney and loaded with fura-2 for measurement of intracellular calcium concentration ([Ca2+]i) using microscope-based photometry. In tissue bathed in Ringer's solution containing 150 mM Na+ and 1.5 mM Ca2+, afferent and efferent arteriolar [Ca2+]i averaged 136 +/- 6 and 154 +/- 7 nM, respectively. Removal of extracellular Na+ increased afferent arteriolar [Ca2+]i by 70 +/- 7 mM, while efferent arteriolar [Ca2+]i only increased by 39 +/- 5 nM (P < 0.01 vs. afferent arteriole). These responses were inhibited by 6 nM Ni2+ and required extracellular Ca2+, but were unaffected by 10 microM diltiazem. After incubation in 500 microM ouabain, 5 microM monensin, and 5 microM nigericin, [Ca2+]i responses to removal of extracellular Na+ were exaggerated significantly, averaging 174 +/- 50 nM in afferent arterioles and 222 +/- 82 nM in efferent arterioles (NS vs. afferent arterioles). Moreover, responses to removal of extracellular Na+ were enhanced by 100 nM phorbol 12-myristate 13-acetate, an affect which was blocked by PKC inhibition (25 nM K252b). These data indicate that both afferent and efferent arterioles express the Na-Ca exchanger, and that PKC activity impacts on exchange capacity in these vessels.