BMS-191011, an Opener of Large-Conductance Ca2+-Activated Potassium Channels, Dilates Rat Retinal Arterioles in Vivo

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The large-conductance Ca2+-activated K+ (BKCa) channels modulate vascular smooth muscle tone but the role of BKCa channels in regulation of retinal circulation remains unclear. In the present study, we examined the effects of BMS-191011 and NS 1619, openers of BKCa channels, on rat retinal blood vessels in vivo. Male Wistar rats (8- to 10-week-old) were anesthetized with pentobarbital sodium (50 mg/kg, intraperitoneally (i.p.)) and treated with tetrodotoxin (50 μg/kg, intravenously (i.v.)) to eliminate any nerve activity and prevent movement of the eye under artificial ventilation. A mixture solution of adrenaline and noradrenaline (9 : 1) was infused to maintain adequate systemic circulation. BMS-191011 (10—100 μg/kg, i.v.) and NS 1619 (0.1—1.0 μg/kg, i.v.) increased the diameter of retinal arterioles without altering systemic blood pressure and heart rate significantly. The vasodilator responses to BMS-191011, but not to NS 1619, were significantly diminished by intravitreal injection of iberiotoxin (an inhibitor of BKCa channels, 20 pmol/eye). These results suggest that BMS-191011 dilates rat retinal arterioles through activation of iberiotoxin-sensitive BKCa channels in vivo. The BKCa channel opener could be considered as a candidate for improving retinal circulation without severe cardiovascular side-effects.
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