In vitro activity: Glyburide (0.03 mM), a sulfonylurea which has been shown to block the ATP-modulated potassium channel in insulin-secreting cells, causes concentration-dependent shifts to the right (up to 100-fold) of the IC50 value for BRL 34915 and diazoxide, and at 1 μM, abolishes the relaxation response to minoxidil sulfate. Glyburide increases the apparent affinity of HDL binding to Scavenger receptor class B type I (SR-BI). Glyburide blocks SR-BI-mediated selective lipid uptake and efflux at a potency similar to that for its inhibition of ABCA1 (IC50 approximately 275-300 mM). Glyburide (6 mM) which reduces the opening of KATP channels, aggravates Ca2+ loading only when applied to dinitrophenol-pretreated myocytes but not when applied with dinitrophenol treatment. Glyburide (10-500 nM) produces a dose-dependent inhibition of the potassium channel openers (PCOs) relaxation time course. Glyburide also reverses existing Pinacidil relaxation regardless of the degree of pre-existing relaxation. Glyburideis is able to produce its blockade regardless of the state of K+ channel activation.