Three components of potassium outward current in cells isolated from the circular layer of guinea-pig ileum.

Three different populations of voltage-activated K+ channels were identified according to their voltage-dependences, inactivation kinetics and sensitivity toward selective K+ channels antagonists in membranes of cells, isolated from the circular layer of guinea-pig ileum by the use of whole-cell voltage clamp method. Under holding potential Vh = -50 mV apamin (10-6 mol/l) inhibited 29 +/- 3% of the whole-cell K+ current (IK) at 0 mV membrane potential. The apamin-blockade component of IK disappeared after blockade of the inward Ca2+ current, while other IK components remained unchanged. Glibenclamide (10-5 mol/l) inhibited 31 +/- 2.6% of IK at 0 mV membrane potential. Cromakalim (5.10-7 mol/l) increased IK, and glibenclamide impeded this increase and reduced IK amplitudes to the same extent as when applied alone. The difference between amplitudes of IK, measured from Vh = -80 mV and the above ones, expressed from Vh = -50 mV, was defined as the potential-dependent part of IK (Kpd). This component formed 36 to 47% of IK in cells clamped at Vh = -80 mV, and was inhibited by charybdotoxin (10-6 mol/l). The physiological role of these components of IK is discussed.