PGI₂ modulates both water and sodium transport in the rabbit cortical collecting duct (RCCD). In order to clarify the role of the PGI₂/IP system in RCCD, we characterized the expression of IP receptors in the rabbit kidney. We show by Northern blotting and Western blotting that IP mRNA and protein was detectable in all three regions of the kidney, though it is more abundant in the outer medulla. To determine how PGI₂ signals in RCCD, we compared the effects of different PGI₂ analogues Iloprost (ILP), carba-prostacyclin (c-PGI₂) and Cicaprost (CCP) in the isolated perfused RCCD. Exposing the tubules to PGI₂ analogues did not increase water flow (Lp) over basal value. While PGI₂ analogues did not reduce an established Lp response to 8-chlorophenylthio-cAMP, they equipotently inhibited AVP-stimulated Lp by 45 %. The inhibitory effect of ILP and c-PGI₂ on AVP-stimulated Lp is partially reversed by the protein kinase C (PKC) inhibitor, staurosporine, and abolished by Pertussis toxin; but no effect was obtained with CCP. In fura-2 loaded RCCD, CCP did not increase the liberation of calcium ([Ca⁺⁺]i) but in the presence of CCP, individual infusion of ILP and PGE₂ increased [Ca⁺⁺]i, suggesting that CCP did not cause desensitization to either ILP and PGE₂. We concluded that ILP and c-PGI₂ activate PKC and the liberation of [Ca⁺⁺]i but not CCP. This suggested an important role for phosphatidylinositol hydrolysis in mediating ILP and c-PGI₂ effects, but not CCP in RCCD.