ACE and non-ACE mediated effect of angiotensin I on intracellular calcium mobilization in rat glomerular arterioles

Because renin and angiotensin I (ANG I) level are high in the renal circulation, the conversion of ANG I is a critical step in the regulation of glomerular hemodynamics. We studied this conversion by investigating the effect of ANG I on intracellular Ca2+concentration ([Ca2+]i) in rat juxtamedullary glomerular afferent and efferent arterioles (AA and EA, respectively). Two types of EA were considered, thin EA and muscular EA, terminating as peritubular capillaries and vasa rectae, respectively. In all arterioles, ANG I elicited [Ca2+]i elevations. Maximal responses of 171 ± 28 (AA), 183 ± 7 (muscular EA), and 78 ± 11 nM (thin EA) (n = 6), similar to those obtained with ANG II, were observed with 100 nM ANG I. The EC50 values were 20 times higher for ANG I than for ANG II in AA (10.2 vs. 0.5) and muscular EA (6.8 vs. 0.4 nM) and 150 times higher in thin EA (15.2 vs. 0.1 nM). ANG I effect was blocked by losartan, indicating that AT1 receptors were involved. The ANG-converting enyzme (ACE) inhibitor lisinopr...