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Department of Molecular and Cellular Pharmacology, University of Miami School of Medicine, FL 33101, USA.

1. Whole-cell patch clamp recording was used to study an ATP-sensitive, sulphonylurea-inhibitable potassium (K+) conductance in freshly dissociated endothelial cells from rabbit arteries. 2. The ATP-sensitive K+ conductance was activated by micromolar concentrations of the K+ channel opener, levcromakalim, and by metabolic inhibition of endothelial cells using dinitrophenol and iodoacetic acid. The current-voltage (I-V) relationship obtained in isotonic K+ solutions was linear between -150 and -50 mV and had a slope conductance of approximately 1 nS. 3. The permeability of the ATP-sensitive K+ conductance determined from reversal potential measurements exhibited the following ionic selectivity sequence: Rb+ > K+ > Cs+ >> Na+ > NH4+ > Li+. 4. Membrane currents activated by either levcromakalim or metabolic inhibition were inhibited by the sulphonylurea drugs, glibenclamide and tolbutamide, with half-maximal inhibitory concentrations of 43 nM and 224 microM and Hill coefficients of 1.1 and 1.2, respectively. Levcromakalim-induced currents were also inhibited by millimolar concentrations of Ba2+ or tetraethylammonium ions in the external solution. 5. Levcromakalim (3 microM) and metabolic inhibition hyperpolarized endothelial cells by approximately 10-15 mV in normal physiological salt solutions. The hyperpolarization induced by levcromakalim or metabolic inhibition was inhibited by bath application of 10 microM glibenclamide. 6. Internal perfusion of the cytosol of whole-cell voltage-clamped endothelial cells with an ATP-free pipette solution activated a membrane current which was reversibly inhibited by internal perfusion with a 3 mM MgATP pipette solution. This current was insensitive to other adenine and guanine nucleotides in the pipette solution. The inward current evoked in a nominally ATP-free internal solution was further increased by bath application of levcromakalim. 7. Levcromakalim (25 microM) did not induce a change in the intracellular Ca2+ concentration of fura-2-loaded endothelial cells, whereas metabolic inhibition caused a slow and sustained increase in intracellular Ca2+ concentration, which was attenuated by 10 microM glibenclamide applied externally.(ABSTRACT TRUNCATED AT 400 WORDS)

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