Potassium and sodium channels in human malignant glioma cells.

Human malignant glioma cells from 5 different cell lines were voltage clamped and examined for the presence of depolarization-activated ion channels. Outward K-currents were elicited at membrane potentials greater than 40 mV, which had two main components, one which was delayed and blocked by externally applied tetraethylammonium (TEA, 10 mM), and another which was instantaneous and insensitive to TEA in the outside solution. The proportion of the two K-current components varied between cell lines. An increase in [Ca2+]o in the range 0-4 mM, decreased the leak conductance and shifted the activation of the instantaneous outward K-current towards more positive potentials. Mg2+, Zn2+ and Co2+ had qualitatively similar effects. Patch recordings with 150-160 mM K+-solution on both sides of the membrane revealed that the delayed outward K-current was carried through large conductance (250-300 pS) channels. Changes in free [Ca2+]i from 0 to 2 x 10(-8) M increased the activation of the large conductance K-channel. Small Na-currents were identified in cells from one cell line (Tp-378MG). The Na-conductance ranged from 0.5 to 7.5 nS in 25% of the cells, and was less than 0.5 nS in 75%. The Na-channels were activated and inactivated at 30-40 mV more positive potentials than in the mammalian peripheral nerve. Tetrodotoxin (100 nM) blocked gNa almost completely.