EFFECT OF EXTERNAL CATION CONCENTRATION AND METABOLIC-INHIBITORS ON MEMBRANE-POTENTIAL OF HUMAN GLIAL-CELLS

1. The effect on membrane potential (E(m)) of low external [K+]0, [Na+]0. and [Ca2+]0. and of metabolic inhibitors was studied in cultured human glial cells (U-787CG) and human glioma cells (Tp-483MG and U-251MG). Whole cells were voltage or current clamped with the tight-seal recording technique. 2. E(m). was - 76 and - 80 mV in glial and glioma cells (mean values in U-787CG and U-251MG, respectively) in a reference external solution with 3.0 mm K+. K+-free external solution caused a rapid and reversible depolarization of these cells by about 26 and 42 mV (respectively). 3. Block of K+ channels with 1 mm Ba2+ in external solution rapidly depolarized the cells (U-251MG) by about 35 mV. 4. Na+-free solutions caused a delayed depolarization by 40-50 mV, which was slowly reversible (in 2 min). 5. Ouabain (1 mm) depolarized the cells by about 4 mV. It did not prevent the effect of K+-free solution. 6. Ca2+-free external solution rapidly depolarized the cells to E(m). about - 17 mV. The combination of either Na+-K+-free or Na+-Ca2+-free solution transiently repolarized the cell, which indicated that the K+ selectivity of the membrane was decreased in both K+- and Ca2+-free solutions. 7. Metabolic inhibitors (carbonyl cyanide p-trifluoromethoxy-phenylhydrazone (FCCP) and 2,4-dinitrophenol (DNP)) rapidly and reversibly depolarized the cells. This effect was not prevented by intracellular perfusion of a strong Ca2+-buffering solution. 8. Voltage clamp revealed only minor changes (< 20%) in the leak conductance (g) of cells that were depolarized by the above-mentioned solutions. 9. Positive polarizing current elicited (in some cells) a regenerative depolarization. The threshold for depolarization was less in low external [K+]0). 10. It is concluded (a) that the resting potential of these glial cells depends on ion channels that are K+ selective only in the presence of external Ca2+ and K+ and (b) that this K+ selectivity may require that E(m) is near the reversal potential for potassium (E(K)) and (c) that the action of Metabolic inhibitors (DNP and FCCP) is different from that in neurones.