Characterization of a calcium-activated potassium channel in human fibroblasts

The cell-attached and inside-out patch clamp techniques were used to record single-channel currents from human epidermal fibroblasts. A large-conductance channel (320 pS in symmetric 140 mM KCl) with high potassium selectivity was observed in many patches, particularly those located at the borders of the cells. The channel exhibited both voltage and calcium sensitivity and, therefore, as regarded as a variety of the large-conductance calcium-activated potassium channels reported in many preparations. Probability density functions, fitted to histograms of open and closed time durations at 35°C, usually displayed a minimum of one open state and two closed states. However, kinetic analysis by the fractal method suggested more complicated behavior, particularly for the closed condition. It was not uncommon to observe several channels in one patch. This was distinguishable from the presence of subconductances, which were also observed. Although this channel could have many roles, it seems likely to mediate the calcium-activated conductance that underlies the hyperpolarizing response of fibroblasts to mechanical, electrical, or chemical stimuli.