RESPONSES OF CEREBRAL ARTERIOLES IN DIABETIC RATS TO ACTIVATION OF ATP-SENSITIVE POTASSIUM CHANNELS

The goal of this study was to determine whether responses of pial arte rioles to activation of ATP-sensitive potassium channels are altered d uring diabetes mellitus. We measured changes in diameter of pial arter ioles in vivo in nondiabetic and diabetic rats (streptozotocin; 50-60 mg/kg ip; studied 3-4 mo after streptozotocin) in response to RP52891, an activator of ATP-sensitive potassium channels. RP52891 (1.0 muM) d ilated pial arterioles in nondiabetic rats by 16 +/- 1% but constricte d pial arterioles in diabetic rats by 2 +/- 2% (means +/- SE; P < 0.05 vs. response in nondiabetic rats). Dilatation of pial arterioles in n ondiabetic rats in response to RP52891 was inhibited by glibenclamide (1.0 muM) but was not altered by N(G)-monomethyl-L-arginine (1.0 muM), apamin (0.1 muM), or charybdotoxin (50 nM). Thus dilatation of pial a rterioles in response to RP52891 appears to be due to activation of AT P-sensitive potassium channels and does not involve nitric oxide or ca lcium-activated potassium channels. To determine whether impaired dila tation of pial arterioles in response to RP52891 in diabetic rats was related to a nonspecific effect of diabetes mellitus on vasodilatation , we measured diameter of pial arterioles in nondiabetic and diabetic rats in response to nitroglycerin. Nitroglycerin (1.0 muM) dilated pia l arterioles by 12 +/- 1 % in nondiabetic rats and 16 +/- 2 % in diabe tic rats (P > 0.05). Thus impaired dilatation of pial arterioles in di abetic rats in response to RP52891 also is not related to a nonspecifi c effect of diabetes mellitus on vasodilatation. The findings of the p resent study suggest that ATP-sensitive potassium channels are functio nal in cerebral arterioles in vivo and are impaired during diabetes me llitus.