Two components of potassium outward current in smooth muscle cells from the circular layer of human jejunum.

Two components of the outward K+ currents (Ik) of cells isolated from the circular layer of human jejunum were investigated using the conventional whole-cell voltage clamp method. A fast transient Ik component could only be elicited by depolarization in cells dialysed with pipette solution of pCa < 7.4. This Ik component was strongly voltage dependent, and could be selectively abolished by 30 mumol/l quinidine. Its amplitudes decreased in the absence of Ca entry, the decrease depending on the duration of cell exposure to media containing calcium-blockers, and disappeared after depletion of intracellular Ca2+ stores. The steady-state component of Ik was sensitive to tetraethylammonium. This component had comparable amplitudes at pCa = 8.4 or pCa = 7.4 of the pipette solution, and was present during a long-lasting exposure of cells to solutions containing Ca(2+)-blocking drugs.