Glomerular Microcirculation: Distinct Intracellular Mechanisms for Afferent and Efferent Arteriolar Tone

摘要

Angiotensin (ANG) II contributes importantly to the regulation of renal pre- and postglomerular arteriolar tone. The present study examined the subcellular signaling mechanisms for ANG II-induced afferent (AFF) and efferent arteriolar (EFF) constriction, using the isolated perfused hydronephrotic rat kidney. Angiotensin Il-induced AFF and EFF constriction was abolished by an ANG II receptor antagonist (losartan). The pretreatment with W-ethylmaleimide (G, protein inhibitor) completely prevented the ANG II-induced constriction of EFF, but not AFF. Furthermore, signal interruption at the phospholipase C level by 2-nitro-4-carboxyphenyl-N,N-diphenyl-carbamate blocked the constriction of both arterioles. Next, ANG II-induced AFF constriction was completely inhibited by the blockade of inositol-1,4,5-trisphosphate (IP3) signaling by thapsigargin and L-type voltage-dependent calcium channel blockers, but relatively refractory to protein kinase C (PKC) inhibition (by chelerythrine). In contrast, EFF constriction was resistant to pranidipine, but partially responsive to thapsigargin and chelerythrine. Finally, direct PKC activation by phorbol myristate acetate caused prominent EFF constriction, which was inhibited by manganese/free calcium medium, but not by pranidipine. Thus, PKC plays an obligatory role in ANG II-induced EFF constriction that requires extracellular calcium entry through nonselective cation channels. By contrast, ANG II-induced AFF constriction is mainly mediated by IP3 and voltage-dependent calcium channel pathways. Collectively, intracellular signaling mechanisms differ in AFF and EFF, which may determine the glomerular function.