Inducible nitric oxide synthase subserves cholinergic vasodilation in retina.
In this paper, we investigate the role of muscarinic acetylcholine receptor (mAChR) activity in the regulation of inducible (i) nitric oxide synthase (iNOS) expression and activity. The signaling pathway involved is also examined. These experiments also provide a link between mAChR activation and the nitric oxide (NO)-dependent regulation of retinal vascular diameter. The diameter of the retinal vessels at a distance of 1 disc diameter from the center of the optic disc was measured in rats using digital retinal photography, and both iNOS-mRNA gene expression and NOS were specifically measured using RT-PCR and [U-(14)C] citrulline assays, respectively. Stimulation of M(1) and M(3) mAChR with carbachol caused an increase in vessel diameter, in iNOS-mRNA levels and in NOS activity in the retina. Aminoguanidine, an inhibitor of iNOS, attenuated all these effects. Inhibitors of phospholipase C (PLC) and protein kinase C (PKC) but not calcium/calmodulin (CaM) prevented the muscarinic-dependent increase in iNOS-mRNA levels. The results obtained suggest that the activation of mAChR increases retinal vessel diameters by increasing the production of nitric oxide (NO) through iNOS activation and iNOS-mRNA gene expression. The mechanism appears to occur secondarily to stimulation of PLC and PKC enzymatic activity.
Berra
Alejandro
A
Department of Pathology, School of Medicine, University of Buenos Aires, Argentina.
Ganzinelli
Sabrina
S
Saravia
Mario
M
Borda
Enri
E
Sterin-Borda
Leonor
L
D000818:Animals; D001120:Arginine / Q000494:pharmacology; D015152:Blotting, Northern / Q000379:methods; D002217:Carbachol / Q000494:pharmacology; D018679:Cholinergic Agonists / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology*; D006146:Guanidines / Q000494:pharmacology; D008297:Male; D018727:Muscarinic Antagonists / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000235:genetics / Q000378:metabolism*; D052247:Nitric Oxide Synthase Type II; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D017208:Rats, Wistar; D011976:Receptors, Muscarinic / Q000502:physiology*; D012160:Retina / Q000187:drug effects / Q000201:enzymology*; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D014664:Vasodilation / Q000187:drug effects / Q000502:physiology*
D018679:Cholinergic Agonists; D004791:Enzyme Inhibitors; D006146:Guanidines; D018727:Muscarinic Antagonists; D012333:RNA, Messenger; D011976:Receptors, Muscarinic; D002217:Carbachol; D001120:Arginine; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; C496318:Nos2 protein, rat; C004479:pimagedine