We used the patch-clamp technique to examine the effect of angiotensin II (AngII) on the basolateral K channels in the thick ascending limb (TAL) of the rat kidney. Application of AngII increased the channel activity and the current amplitude of the basolateral 50 pS K channel. The stimulatory effect of AngII on the K channels was completely abolished by losartan, an inhibitor of type 1 angiotensin receptor (AT1R), but not by PD123319, an AT2R antagonist. Moreover, inhibition of phospholipase C (PLC) and protein kinase C (PKC) also abrogated the stimulatory effect of AngII on the basolateral K channels in the TAL. This suggests that the stimulatory effect of AngII on the K channels was induced by activating PLC and PKC pathways. Western blotting demonstrated that AngII increased the phosphorylation of c-Src in tyrosine residue 416, an indication of c-Src activation. This effect was mimicked by PKC stimulator but abolished by calphostin C. Moreover, inhibition of NADPH oxidase (NOX) also blocked the effect of AngII on c-Src tyrosine phosphorylation. The role of Src-family protein tyrosine kinase (SFK) in mediating the effect of AngII on the basolateral K channel was further suggested by the experiments in which inhibition of SFK abrogated the stimulatory effect of AngII on the basolateral 50 pS K channel. We conclude that AngII increases basolateral 50 pS K channels activity via AT1R and that activation of AT1R stimulates SFK by a PLC-PKC-NOX-dependent mechanism.