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A.A. Rocha-Sousa, F.M. Falcão-Reis, A.A. Leite-Moreira; Selective ETB Stimulation Relaxes the Iris Sphincter Muscle . Invest. Ophthalmol. Vis. Sci. 2003;44(13):4425.
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Purpose:: Endothelin–1 (ET-1) effects are mediated by two different receptors (ETA and ETB). ETA stimulation promotes vasoconstriction, myosis and hypertrophy, while ETB stimulation causes vasodilation, ocular hypotension and release nitric oxide (NO) and prostaglandins (Pg). The present study investigated the effects of selective ETB stimulation in iris sphincter muscle. Methods: Rabbit iris sphincter muscles (n=29) were dissected and mounted on a vertical organ bath containing a modified Krebs-Ringer solution (1.8 mM Ca2+; 35°C) and were attached to a force transducer. We studied the effects of Sarafotoxin (SRTX; 0.2 µM) alone (n=9) or in presence of: (i) a selective ETA receptor antagonist, BQ-123 (0.1 µM ; n=7); (ii) a selective ETB antagonist, BQ 788 (0.1 µM; n=8) and (iii) a NOS inhibitor, L-nitro-arginine (L-NA; 90µM; n=5). The effects were recorded and analysed after an isometric contraction elicited by Carbachol (0.1 µM). Only significant results (mean ±SE, p<0.05) are given, expressed as % changes from control. Results: When compared to control, SRTX promoted a 3.2±1.1% decrease in isometric tension, 2’ 30’’ after its addition to the bathing solution, an effect that disappeared at 10’. This effect was not affected by BQ-123 (tension decreased 3.0±0.7) slightly but not significantly decreased by L-NA (tension decreases 2.6±1.9); yet it was abolished by BQ-788 (tension increases 0.5±0.8). Conclusions: SRTX relaxes the iris sphincter muscle. This effect is mediated by ETB receptors stimulation and is almost independent of NO production. View OriginalDownload SlideView OriginalDownload Slide
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