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

To investigate whether in isolated porcine ciliary processes, stimulation of the nitric oxide (NO)-guanylate cyclase (GC)-3',5'-cyclic guanosine monophosphate (cGMP) pathway modulates ciliary epithelial transmembrane potential.

Changes in transmembrane potential induced by the two NO donors, sodium nitroprusside (SNP; 100 microM) and S-nitroso-N-acetyl-penicillamine (SNAP; 100 microM), or by the cGMP-analogue 8-para-chlorophenylthioguanosine-3', 5'-cyclic guanosine monophosphate (8-pCPT-cGMP; 100 microM) were measured with 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 microM). The effect of 8-pCPT-cGMP was also assessed in the presence of the anion channel inhibitors niflumic acid (100 microM), diisothiocyanatostilbene-2,2' disulfonic acid (DIDS; 1 mM), anthracene-9-carboxylic acid (9-AC; 1 mM), or the K+ channel blocker tetraethylammonium chloride (TEA; 10 mM). cGMP production was measured by immunoassay.

Significant membrane depolarizations (P < 0.05-0.001; n = 5-8) were induced by SNP (6 +/- 1 mV; mean +/- SEM), SNAP (8 +/- 1 mV), or 8-pCPT-cGMP (13 +/- 1 mV). In presence of ODQ, the effect of SNP and SNAP were significantly 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 prevented (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 production induced by SNP (9.5-fold) was inhibited by ODQ (P < 0.001; n = 6).

Activation of the NO-GC-cGMP pathway modulates epithelial transmembrane potential in isolated porcine ciliary processes.