NO/cGMP pathway activation and membrane potential depolarization in pig ciliary epithelium

PURPOSE. TO investigate whether in isolated porcine ciliary processes, stim ulation of the nitric oxide (NO)-guanylate cyclase (GC)-3',5'-cyclic guanos ine monophosphate (cGMP) pathway modulates ciliary epithelial transmembrane potential. METHODS. Changes in transmembrane potential induced by the two NO donors, s odium nitroprusside (SNP; 100 mu M) and S-nitroso-N-acetyl-penicillamine (S NAP; 100 mu M), or by the cGMP-analogue 8-para-chlorophenylthioguanosine-3' ,5'-cyclic guanosine monophosphate (8-pCPT-cGMP; 100 mu M) were measured wi th microelectrodes in the presence or in the absence of the GC-inhibitor 1- H(1,2,4)oxadiazole(4,3-alpha)quinoxalin-1-1 (ODQ; 10 mu M). The effect of 8 -pCPT-cGMP was also assessed in the presence of the anion channel inhibitor s niflumic acid (100 mu M), diisothiocyanatostilbene-2,2' disulfonic acid ( DIDS; 1 mM), anthracene-9-carboxylic acid (9-AC; 1 mM, or the K+ channel bl ocker tetraethylammonium chloride (TEA; 10 mM). cGMP production was measure d by immunoassay. RESULTS. Significant membrane depolarizations (P < 0.05-0.001; n = 5-8) wer e induced by SNP (6 +/- 1 mV; mean +/- SEM), SNAP (8 +/- 1 mV), or 8-pCPT-c GMP (13 +/- 1 mV). In presence of ODQ, the effect of SNP and SNAP were sign ificantly inhibited (-2 +/- 0 mV and 0 +/- 0 mV, respectively; P < 0.05; n = 5-6), but not depolarizations elicited by 8-pCPT-cGMP. These were prevent ed (P < 0.05-0.01; n = 5) by niflumic acid(1 +/- 1 mV), DIDS (1 +/- 1 mV), or 9-AC (5 +/- 1 mV), but not by TEA (12 +/- 2 mV). The increase in cGMP pr oduction induced by SNP (9.5-fold) was inhibited by ODQ (P < 0.001; n = 6). CONCLUSIONS. Activation of the NO-GC-cGMP pathway modulates epithelial tran smembrane potential in isolated porcine ciliary processes.