Dissimilar mechanisms of Ca2+response to bradykinin in different types of juxtamedullary glomerular arterioles

Bradykinin (BK)-induced changes in intracellular calcium level ([Ca2+]i) were studied on fura 2-loaded afferent (AA) and efferent glomerular arterioles (EA) microdissected from juxtamedullary renal cortex. A distinction was made between thin and muscular EA. In AA and both types of EA, BK increased [Ca2+]ithrough activation of B2 receptors located only on the endothelium. The responses were not affected by nifedipine (10−6 M) and were smaller in a Ca2+-free medium, providing evidence that BK opens voltage-independent Ca2+ channels and mobilizes intracellular Ca2+. Thin EA differed from AA and muscular EA by a lower sensitivity to BK (EC50 = 6.95 ± 3.81 vs. 0.21 ± 0.08 and 0.18 ± 0.13 nM, respectively;P < 0.05), a higher maximal response (89 ± 5 vs. 57 ± 5 and 44 ± 7 nM;P < 0.001), and a spontaneous return to basal Ca2+ level, even in the presence of BK. Genistein (10−4 M) and herbimycin A (25 × 10−6M), specific inhibitors of tyrosine kinases, inhibited the [Ca2+]iresponses exclusively in AA. Genistein red...