Voltage-dependent K+ current in capillary endothelial cells isolated from guinea pig heart

Capillary fragments were isolated from guinea pig hearts, and their electri cal properties were studied using the perforated-patch and cell-attached mo de of the patch-clamp technique. A voltage-dependent K+ current was discove red that was activated at potentials positive to -20 mV and showed a sigmoi d rising phase. For depolarizing voltage steps from -128 to +52 mV, the tim e to peak was 71 +/- 5 ms (mean +/- SE) and the amplitude of the current wa s 3.7 +/- 0.5 pA/pF in the presence of 5 mM external K+. The time course of inactivation was exponential with a time constant of 7.2 +/- 0.5 s at +52 mV. The current was blocked by tetraethylammonium (inhibitory constant simi lar to 3 mM) but was not affected by charybdotoxin (1 mu M) or apamin (1 mu M) In the cell-attached mode, depolarization-activated single-channel curr ents were found that inactivated completely within 30 s; the single-channel conductance was 12.3 +/- 2.4 pS. The depolarization-activated K+ current d escribed here may play a role in membrane potential oscillations of the end othelium.