The cortical thick ascending limb (CTAL) coexpresses angiotensin II (AngII)/ angiotensin III (AngIII) receptor type 1A (AT_1A-R) and bradykinin (BK) receptor type 2 (B₂-R). In several cell types, these two receptors share the same signaling pathways, although their physiological functions are often opposite. In CTAL, little is known about the intracellular transduction events leading to the final physiological response induced by these two peptides. We investigated and compared in this segment the action of AngII/III and BK on [Ca²⁺]_i response and metabolic CO₂ production, an index of Na⁺ transport, by using inhibitors of PKC (bisindolylmaleimide), Src tyrosine kinase (herbimycin A and PP2) and MAPK/ERK (PD98059 and UO126). AngII/III and BK (10^-7mol/liter) released Ca²⁺ from the same intracellular pools, but activated different Ca²⁺ entry pathways. AngII/III- or BK-induced [Ca²⁺]_i increases were similarly potentiated by bisindolylmaleimide. Herbimycin A and PP2, decreased similarly the [Ca²⁺]_i responses induced by AngII/III and BK. In contrast, PD98059 and UO126 affected the effects of BK to a larger extent than those of AngII/III. Especially, the Ca²⁺ influx induced by BK was more strongly inhibited than that induced by AngII/III in the presence of both compounds. The Na⁺ transport was inhibited by BK and stimulated by AngII/III. The inhibitory action of BK on Na⁺ transport was blocked by UO126, whereas the stimulatory response of AngII/III was potentiated by UO126, but blocked by bisindolylmaleimide. These data suggest that the inhibitory effect of BK on Na⁺ transport seems to be directly mediated by an increase in Ca²⁺ influx dependent of MAPK/ERK pathway activation. In contrast, the stimulatory effect of AngII/III on Na⁺ transport is more complex and involves PKC and MAPK/ERK pathways.