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Institut für Normale und Pathologische Physiologie, Universität Marburg, Germany.

1. Inwardly rectifying K+ (IK(IR)) currents of freshly dissociated coronary endothelial cells from guinea-pig heart were investigated with the perforated-patch technique. 2. The whole-cell current-voltage relationship of endothelial cells showed strong inward rectification. Increasing the extracellular K+ resulted in an increase of inward currents. The slope conductance of the cells in the potential range negative to the calculated potassium equilibrium potential (EK) with 5, 60 and 150 mM external potassium was 0.18 +/- 0.14, 0.55 +/- 0.50 and 0.63 +/- 0.29 nS (mean +/- S.D.), respectively. 3. To quantify the steepness of inward rectification, the voltage dependence of the chord conductance of the cells was fitted with a Boltzmann function. The slope factor k describing the steepness of the relationship was 6.8 +/- 1.5 mV. 4. Extracellular barium induced a potential- and time-dependent block of inward currents through endothelial KIR channels. Half-maximum inhibition of IK(IR) currents was achieved with < or = 1 microM barium at a membrane potential of -70 mV in a solution containing 60 mM K+. 5. Whole-cell inward currents revealed the opening and closing of single KIR channels. The single-channel conductance was 26 +/- 3 pS with 60 mM external K+ and 33 +/- 6 pS with 150 mM external K+. 6. Our results suggest that the electrical properties of freshly dissociated endothelial cells are to a large extent determined by five to sixty active strong inwardly rectifying K+ (KIR) channels.

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