Properties of a potassium-selective ion channel in human melanoma cells.

Currents through ion channels were measured from cells of a human melanin-producing melanoma cell line (IRG 1) with the patch clamp technique. In these cells the most frequently observed channel is a potassium channel. The channel activates slowly at depolarizing voltage steps but does not inactivate. Single channel potassium currents can be measured in cell-attached patches at the resting potential of melanoma cells. The channel has a conductance of approximately 10 pS. As measured from the reversal potentials of single channel currents, the permeability ratio for sodium and potassium, PNa/PK, is between 0.03 and 0.04. Open probability is increased at positive potentials. Mean open times are prolonged at voltage steps to more positive potentials. Closed time histograms are fitted by two exponentials. The slow shut time is decreased at positive potentials. In whole cell measurements, cell conductance measured between -20 and + 70 mV was reduced by 10 mM tetraethylammonium chloride from 6.4 +/- 1.2 nS (n = 4) to 0.8 +/- 0.3 nS (n = 3). Application of isoproterenol decreases the probability of the channel being open without any change in the single channel conductance. A possible role of the 10 pS potassium channel in the growth of melanoma cells is discussed.