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Abstract #18382 Published in IGR 3-3
Carbachol and nitric oxide inhibition of Na,K-ATPase activity in bovine ciliary processes
Ellis DZ; Nathanson JA; Rabe J; Sweadner KJInvestigative Ophthalmology and Visual Science 2001; 42: 2625-2631
PURPOSE: Nitric oxide (NO) donors and cholinergic agents decrease intraocular pressure, in part because they induce a decrease in aqueous humor production. Because Na,K-adenosine triphosphatase (ATPase) is involved in aqueous humor formation, this study was conducted to investigate the hypothesis that NO and cholinomimetics regulate its activity in bovine ciliary processes. METHODS: Bovine tissue slices were incubated with agonists and antagonists in a physiological buffer in vitro. Na,K-ATPase activity was determined by assaying hydrolysis of adenosine triphosphate (ATP) in suspended permeabilized tissue slices. RESULTS: Carbachol-induced inhibition of Na,K-ATPase activity correlated with increases in cGMP. This inhibition was abolished by the muscarinic blocker atropine, the NO inhibitor NW-nitro-L-arginine (L-NAME) and the soluble guanylate cyclase inhibitor 1H[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ). Sodium nitroprusside (SNP) mimicked the actions of carbachol. The SNP-induced decrease in Na,K-ATPase activity correlated with an increase in cGMP and was also abolished by ODQ. Both 8-bromo (Br-cGMP and okadaic acid also inhibited Na,K-ATPase activity. CONCLUSIONS: Carbachol-induced inhibition of Na,K-ATPase activity involves muscarinic receptor activation. That SNP mimics and L-NAME reverses carbachol's effect on Na,K-ATPase activity suggests that the actions of carbachol are mediated by NO. Carbachol's and SNP's effects on Na,K-ATPase activity involved soluble guanylate cyclase and cGMP. Inhibition of Na,K-ATPase activity by 8-Br-cGMP and okadaic acid indicates that protein phosphorylation events may mediate SNP-induced inhibition of Na,K-ATPase activity.
Dr D.Z. Ellis, 149-6118 Massachusetts General Hospital, 149 13th Street, Charlestown, MA 02129, USA. ellis@helix.mgh.harvard.edu
Classification:
11.2 Cholinergic drugs (Part of: 11 Medical treatment)
