Morphological heterogeneity of renal glomerular arterioles and distinct [Ca2+]i responses to ANG II

The present study compares cytosolic calcium concentration ([Ca2+]i) responses to angiotensin II (ANG II) of afferent (AA) and efferent arterioles (EA) by taking account of the localization and morphological differences of EA. In outer cortex, 1 nM ANG II induced smaller [Ca2+]i increases in thin EA than in AA[48 +/- 10 (n = 12) vs. 94 +/- 7 nM (n = 11); P < 0.001]. In inner cortex, two types of EA were considered, i.e., thin and muscular ones. The response to 1 nM ANG II was 35% lower in thin than in muscular EA (P < 0.05) but did not differ from that obtained with corresponding AA. In EA of the outer cortex, 1 microM nifedipine, a dihydropyridine blocker of voltage-operated channels (VOCC), did not affect calcium influx, which was suppressed by 1 mM NiCl2, a nonselective calcium entry blocker. In other arterioles, nifedipine inhibited by approximately 40% calcium entry, and remaining influx was blocked by NiCl2. These results indicate a relationship between the magnitude of [Ca2+]i responses, activation of dihydropyridine-sensitive VOCC by ANG II, and the muscular morphology in renal glomerular arterioles. They suggest that ANG II regulates differently local renal microcirculation. They do not, however, support the hypothesis of a greater sensitivity to ANG II of EA compared with the AA of a given nephron.