Inhibition of KATP channel activity augments baroreflex-mediated vasoconstriction in exercising human skeletal muscle

In the present investigation we examined the role of ATP-sensitive potassium (K(ATP)) channel activity in modulating carotid baroreflex (CBR)-induced vasoconstriction in the vasculature of the leg. The CBR control of mean arterial pressure (MAP) and leg vascular conductance (LVC) was determined in seven subjects (25 +/- 1 years, mean +/- S.E.M.) using the variable-pressure neck collar technique at rest and during one-legged knee extension exercise. The oral ingestion of glyburide (5 mg) did not change mean arterial pressure (MAP) at rest (86 versus 89 mmHg, P > 0.05), but did appear to increase MAP during exercise (87 versus 92 mmHg, P = 0.053). However, the CBR-MAP function curves were similar at rest before and after glyburide ingestion. The CBR-mediated decrease in LVC observed at rest (approximately 39%) was attenuated during exercise in the exercising leg (approximately 15%, P < 0.05). Oral glyburide ingestion partially restored CBR-mediated vasoconstriction in the exercising leg (approximately 40% restoration, P < 0.05) compared to control exercise. These findings indicate that K(ATP) channel activity modulates sympathetic vasoconstriction in humans and may prove to be an important mechanism by which functional sympatholysis operates in humans during exercise.