Hyperosmolality dilates rat skeletal muscle arterioles: role of endothelial K(ATP) channels and daily exercise

The purpose of this study was to investigate the mechanism underlying arteriolar responses to hyperosmolality and to determine the effects of daily exercise on this response. Dilator responses were measured in isolated, cannulated, and pressurized skeletal muscle arterioles. Osmolality was increased from approximately 290 to 330 mosmol/kgH(2)O by adding glucose, sucrose, or mannitol to the superfusion solution. All three compounds elicited similar changes in vessel diameter, suggesting that this response was due to changes in osmolality. Responses to glucose were abolished by endothelium removal but were not altered in endothelium-intact vessels by superfusion with the nitric oxide synthase inhibitor N(omega)-nitro-L-arginine or the cyclooxygenase inhibitor indomethacin. In endothelium-intact arterioles, responses to glucose superfusion with the ATP-sensitive potassium (K(ATP)) channel inhibitor glibenclamide; however, intraluminal perfusion with glibenclamide nearly abolished the responses to glucose and mannitol. Intraluminal administration of glucose elicited a significantly greater dilation than extraluminal glucose. The response to intraluminal glucose was also inhibited by intraluminal glibenclamide. Four weeks of daily exercise did not significantly alter the responses to hyperosmolality in gracilis or soleus muscle arterioles. These data demonstrate that physiological increases in intraluminal osmolality dilate rat skeletal muscle arterioles via activation of endothelial K(ATP) channels; however, this endothelium-dependent response is not augmented by daily exercise.