Calcium- and Voltage-Activated Potassium Channels in Human Macrophages

摘要

Single calcium-activated potassium channel currents were recorded in intact and excised membrane patches from cultured human macrophages. Channel conductance was 240 pS in symmetrical 145 mM K(+) and 130 pS in 5 mM external K(+). Lower conductance current fluctuations (40% of the larger channels) with the same reversal potential as the higher conductance channels were noted in some patches. Ion substitution experiments indicated that the channel is permeable to potassium and relatively impermeable to sodium. The frequency of channel opening increased with depolarization and intracellular calcium concentration. At .0000001 M, channels activity was evident only at potentials of +40mV or more deplorized while at .00001 M, channels were open at all voltages tested (-40 to +60 mV). In intact patches, channels were seen at depolarized patch potential of +50 mV or greater, indicating that the ionized calcium concentration in the macrophage is probably less than .00001 M.