MORPHOLOGICAL HETEROGENEITY OF RENAL GLOMERULAR ARTERIOLES AND DISTINCT [CA2-II(](I) RESPONSES TO ANG)

The present study compares cytosolic calcium concentration ([Ca2+](i)) responses to angiotensin II (ANG II) of afferent (AA) and efferent ar terioles (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 n M (n = 11); P < 0.001]. In inner cortex, two types of EA were consider ed, 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 t hat obtained with corresponding AA. In EA of the outer cortex, 1 mu M nifedipine, a dihydropyridine blocker of voltage-operated channels (VO CC), did not affect calcium influx, which was suppressed by 1 mM NiCl2 , a nonselective calcium entry blocker. In other arterioles, nifedipin e inhibited by similar to 40% calcium entry, and remaining influx was blocked by NiCl2. These results indicate a relationship between the ma gnitude of [Ca2+](i) responses, activation of dihydropyridine-sensitiv e VOCC by ANG II, and the muscular morphology in renal glomerular arte rioles. They suggest that ANG II regulates differently local renal mic rocirculation. They do not, however, support the hypothesis of a great er sensitivity to ANG II of EA compared with the AA of a given nephron .