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 nM, while efferent arteriolar [Ca²⁺](i) only increased by 39 ± 5 nM (P < 0.01 vs. afferent arteriole). These responses were inhibited by 6 mM Ni²⁺ and required extracellular Ca²⁺, but were unaffected by 10 μM diltiazem. After incubation in 500 μM ouabain, 5 μM monensin, and 5 μM 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 effect 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.