A NOVEL CGMP-ACTIVATED CL- CHANNEL IN RENAL PROXIMAL TUBULES

Cl- channels activated by natriuretic peptides were detected in cultur ed rat proximal convoluted tubule (PCT) cells with the use of patch-cl amp methodology. Bath application of atrial natriuretic peptide (ANP) activates a 150-pS Cl- channel with the open probability (P-o) of the channel increasing from 0.0008 +/- 0.0003 to 0.021 +/- 0.008. 8-Bromog uanosine 3',5'-cyclic monophosphate (8-BrcGMP), a membrane-permeable a nalogue of cGMP, increased channel activity in the on-cell mode. In in side-out patches the channel was activated by cGMP in a dose-dependent manner. Channel activity decreased after washing out and increased an reapplication of cGMP. A similar activation was observed also in pres ence of either of two protein kinase inhibitors, N-[2-(methylamino)eth yl]-5-isoquinolinesulfonamide dihydrochloride or KT5823, or a phosphat ase inhibitor. Bath application of urodilatin mimicked the action of A NP. P-o of the channel was found to be independent of both voltage and Ca2+, and gating activity could be blocked by the stilbene, 4,4-dinit rostilbene-2,2-disulfonic acid. These results demonstrate a Cl- conduc tance in PCT cells modulated by ANP and urodilatin via their second me ssenger, cGMP.