Carbachol and nitric oxide inhibition of Na,K-ATPase activity in bovine ciliary processes.
OBJECTIVE
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 N(w)-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.
Ellis
D Z
DZ
Neuroscience Center, Massachusetts General Hospital, Charlestown, MA 02129, USA. ellis@helix.mgh.harvard.edu
Nathanson
J A
JA
Rabe
J
J
Sweadner
K J
KJ
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D002217:Carbachol / Q000494:pharmacology*; D002417:Cattle; D018679:Cholinergic Agonists / Q000494:pharmacology*; D002924:Ciliary Body / Q000187:drug effects* / Q000201:enzymology; D006152:Cyclic GMP / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009569:Nitric Oxide / Q000494:pharmacology*; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors*
D018679:Cholinergic Agonists; D004791:Enzyme Inhibitors; C016276:8-bromocyclic GMP; D009569:Nitric Oxide; D001285:Atropine; D000255:Adenosine Triphosphate; D002217:Carbachol; D000254:Sodium-Potassium-Exchanging ATPase; D006152:Cyclic GMP; D019331:NG-Nitroarginine Methyl Ester