Potassium channels in human and avian fibroblasts

The cell-attached and excised inside-out patch-clamp techniques were used to study single-channel characteristics of potassium channels in cultured human and avian fibroblasts. Six different potassium channels were distinguished with conductances of 235 +/- 25, 190 +/- 57, 114 +/- 27, 77 +/- 14, 40 +/- 6 and 21 +/- 4 pS in symmetric 140 mM potassium solutions. The channels were separable by their conductances, ion-selectivities, voltage-sensitivities and kinetic properties. All six channels were found in both fully differentiated human skin fibroblasts and primary cultures of 72 h chick sclerotome. The largest channel (235 pS) had a steep bimodal voltage dependence, being open only around the resting membrane potential. It was imperfectly selective for potassium, having a relative sodium:potassium permeability of 0.3. The 190 pS channel was very potassium-selective, had an S-shaped voltage sensitivity and was calcium-dependent. The two intermediate-size channels (114 and 77 pS) had open probabilities of less than 0.5 under all of the conditions we used. They were not completely selective for potassium and were not voltage-sensitive. The two smallest channels (40 and 21 pS) were not well characterized. They both had open probabilities of less than 0.2 and showed no evidence of voltage-sensitivity. The 40 pS channel seemed highly potassium-selective. A suction stimulus was used to test all observed channels for mechanosensitivity but none of the six potassium channels was mechanosensitive. Another small channel, with very clear mechanical sensitivity, was seen on a few occasions; this channel has not yet been characterized.