Real-time direct measurement of nitric oxide in bovine perfused eye trabecular meshwork using a clark-type electrode.
NO was detected in bovine trabecular meshwork (TM). Bovine eyes were perfused (posterior ciliary artery). In some eyes (operated eyes) a NO electrode was inserted adjacent to the TM (scleral flap). Vascular perfusion/intraocular pressures (VPP/IOP) were recorded. In operated eyes, epinephrine (1 nM-100 microM) increased NO (maximally 979.9 +/- 117.6 nM, mean +/- SDM). Timolol (1 mM) shifted the epinephrine-NO concentration-response curve rightward (2.94 log units) without significantly changing the maximal response (903.0 +/- 67.7 nM, mean +/- SDM). The non-selective NO synthase (NOS) inhibitor L-NMMA (100 microM) virtually abolished the NO response to epinephrine. L-NMMA alone (1 microM-100 microM) significantly reduced tonic NO generation (maximally 109.5 +/- 24.9 nM, mean +/- SDM), whereas timolol alone (1 microM-1 mM) had no effect. In unoperated eyes, epinephrine (1 nM-100 microM) reduced IOP (maximally 2.56 +/- 0.64 mmHg, mean +/- SDM). Epinephrine (100 microM) mildly increased VPP (4.6 +/- 1.3 mmHg, mean +/- SDM). Baseline aqueous humor formation rate (11.5 +/- 3.2 microl/min, mean +/- SDM) was unaffected. Effluent perfusate (effusate) total NO(2)(-) was determined by enzymatically reducing all NO(3)(-) to NO(2)(-), then assessing resultant NO(2)(-) (Griess assay). Epinephrine (1 nM-1 microM) increased effusate NO(2)(-) (maximally 15.8 +/- 4.9 microM, mean +/- SDM). Timolol (1 mM) reduced, and L-NMMA (100 microM) virtually abolished effusate NO(2)(-) response to epinephrine. L-NMMA alone (1 microM-100 microM) reduced tonic effusate NO(2)(-) (maximally from 5.8 +/- 1.6 microM to 1.1 +/- 0.9 microM, mean +/- SDM), whereas timolol alone (1 microM-1 mM) had no effect. NO is generated tonically in bovine TM and increases in response to epinephrine.
Millar
J C
JC
Department of Biology & Health Science, Faculty of Science, Technology & Design, University of Luton, Park Square Campus, Luton, England. cameron.millar@alconlabs.com
D000818:Animals; D001082:Aqueous Humor / Q000187:drug effects / Q000378:metabolism; D002417:Cattle; D004305:Dose-Response Relationship, Drug; D004563:Electrochemistry; D004837:Epinephrine / Q000493:pharmacokinetics; D007429:Intraocular Pressure / Q000187:drug effects; D009569:Nitric Oxide / Q000032:analysis* / Q000096:biosynthesis / Q000378:metabolism; D019001:Nitric Oxide Synthase / Q000493:pharmacokinetics; D009573:Nitrites / Q000737:chemistry / Q000378:metabolism; D010477:Perfusion; D013999:Timolol / Q000493:pharmacokinetics; D014129:Trabecular Meshwork / Q000737:chemistry* / Q000187:drug effects* / Q000378:metabolism; D019323:omega-N-Methylarginine / Q000493:pharmacokinetics
D009573:Nitrites; D019323:omega-N-Methylarginine; D009569:Nitric Oxide; D013999:Timolol; D019001:Nitric Oxide Synthase; D004837:Epinephrine