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NO/cGMP Pathway Activation and Membrane Potential Depolarization in Pig Ciliary Epithelium

¹ From the Laboratory of Ocular Pharmacology and Physiology, University Eye Clinic Basel; and the ² Department of Zoology and Animal Biology, Sciences III, Geneva University, Switzerland.

PURPOSE. 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.

METHODS. Changes in transmembrane potential induced by the two NO donors, sodium nitroprusside (SNP; 100 µM) and S-nitroso-N-acetyl-penicillamine (SNAP; 100 µM), or by the cGMP-analogue 8-para-chlorophenylthioguanosine-3',5'-cyclic guanosine monophosphate (8-pCPT-cGMP; 100 µM) were measured with microelectrodes in the presence or in the absence of the GC-inhibitor 1-H-(1,2,4)oxadiazole(4,3-)quinoxalin-1-1 (ODQ; 10 µM). The effect of 8-pCPT-cGMP was also assessed in the presence of the anion channel inhibitors niflumic acid (100 µM), 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.

RESULTS. 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).

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

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