Arginine analogues inhibit responses mediated by ATP-sensitive K+ channels

H. A. Kontos and E. P. Wei Department of Medicine, Medical College of Virginia, Virginia Commonwealth University, Richmond 29298, USA. Because arginine analogues have been reported to block the vasodilator response to hypercapnia, we investigated the effect of nitro-L-arginine (L-NNA) on the dilation of pial arterioles to arterial hypercapnia induced by inhalation of 3, 5, and 7% CO2 in anesthetized cats equipped with cranial windows. L-NNA at 250 microM, but not at lower concentrations, significantly reduced hypercapnia-induced dilation. This effect could be reversed by L-arginine. However, hypercapnic hyperemia is not the result of increased guanosine 3',5'-cyclic monophosphate via the usual NO-mediated activation of guanylate cyclase, because application of LY-83583, which blocks guanylate cyclase, did not alter the vessel response to CO2. L-NNA at 250 microM also abolished the pial arteriolar dilation in response to cromakalim, minoxidil, and pinacidil, three known openers of ATP-sensitive K+ channels, and this effect could be reversed by L-arginine. Application of glyburide, which blocks ATP-sensitive K+ channels, also reduced the response to CO2. Subsequent application of L-NNA in these experiments had no additional effect. Vasodilation induced by sodium nitroprusside and 3-morpholinosydnonimine, two known NO donors, was unaffected by glyburide. NG-monomethyl-L-arginine had effects similar to those of L-NNA in the cat and rat at concentrations as low as 20 microM. Our findings suggest that arginine analogues inhibit hypercapnic vasodilation by blocking ATP-sensitive K+ channels, independently of activation of guanylate cyclase via increased production of NO. Furthermore, the data suggest that ATP-sensitive K+ channels may have an arginine site that influences their function.