COX-dependent and -independent pathways in bradykinin-induced anion secretion in rat epididymis

Lysylbradykinin (LBK) added to the apical or basolateral side of cultured rat epididymal monolayers stimulated a rise in short-circuit current (Isc) due to anion secretion. The concentration- response relationships for the apical and basolateral applications have EC50 value of 0.001 muM. The responses to apical or basolateral application of LBK were blocked by WIN64338, a specific B-2 receptor antagonist, but not by Des-Arg(9),[Leu(8)]-BK, a specific B-1 receptor antagonist, indicating that the LBK effects were mediated through B-2 bradykinin receptors. Experiments to desensitize the B-2 receptors by repeated stimulation have demonstrated that the responses to apical or basolateral LBK were due to discrete receptors on the apical or basolateral surface. In epithelia clamped in the Ussing chambers, addition of LBK to the apical or basolateral surface evoked release of PGE(2) into the apical and basolateral bathing solutions over the first 10 min following hormone addition. LBK added to the basolateral side elicited a greater release than it was added to the apical side. Pretreatment of the epithelia with piroxicam (5 muM) abolished PGE(2) release elicited by apical or basolateral LBK and abrogated the Isc induced by basolateral LBK. However, the rise in Isc induced by apical LBK was reduced by 31.3% only. The anion secretion response to apical LBK was not affected by MDL-1 12330A, an adenylate cyclase inhibitor, but greatly attenuated by thapsigargin, an inhibitor of intracellular Ca2+ release. However, the reverse effects were seen for basolateral LBK. It is concluded that distinct pathways are involved in the stimulation of anion secretion by apical or basolateral LBK. The response to basolateral LBK was COX-dependent, mediated by PGE(2) and involves cAMP as second messenger. in contrast, the response to apical LBK is largely COX-independent, not mediated by PGE(2) and involves Ca2+ as intracellular messenger. (C) 2002 Wiley-Liss, Inc.