Jak2 and Ca2+/calmodulin are key intermediates for bradykinin B2 receptor-mediated activation of Na+/H+ exchange in KNRK and CHO cells

Na+/H+ exchangers are ubiquitous in mammalian cells, carrying out key functions, such as cell volume defense, acid-base homeostasis, and regulation of the cytoskeleton. We used two screening technologies (FLIPR and microphysiometry) to characterize the signal transduction pathway used by the bradykinin beta(2) receptor to activate Na+/H+ exchange in two cell lines, KNRK and CHO. In both cell types, beta(2) receptor activation resulted in rapid increases in the rate of proton extrusion that were sodium-dependent and could be blocked by the Na+/H+ exchange inhibitors EIPA and MIA or by replacing extracellular sodium with TMA. Activation of Na+/H+ exchange by bradykinin was concentration-dependent and could be blocked by the selective beta(2) receptor antagonist HOE140, but not by the beta(1) receptor antagonist des-Arg(10)-HOE140. Inhibitors of Jak2 tyrosine kinase (genistein and AG490) and of CAM (W-7 and calmidazolium) attenuated bradykinin-induced activation of Na+/H+ exchange. Bradykinin induced formation of a complex between CAM and Jak2, supporting a regulatory role for Jak2 and CAM in the activation of Na+/H+ exchange in KNRK and CHO cells. We propose that this pathway (beta(2) receptor --> Jak2 --> CAM --> Na+/H+ exchanger) is a fundamental regulator of Na+/H+ exchange activity.