A PROTON PUMP CONTRIBUTES TO NEUROBLASTOMA X GLIOMA CELL-MEMBRANE POTENTIALS

The contribution of an electrogenic proton pump to the membrane potent ial of neuroblastoma x glioma hybrid NG 108-15 cells was determined wi th whole-cell voltage and current recordings and cell volume measureme nts with the preparation bathed in symmetrical 140 mM KCl solutions. T he effects of the K+ channel blockers tetraethylammonium and 4-aminopy ridine and of the H+-ATPase inhibitor bafilomycin A1 on the membrane p otential and input resistance revealed that the membrane potential is generated by an outward H+ pump current of 5-15 pA in equilibrium with an inward passive current. This conclusion is supported by both curre nt- and voltage-clamp results obtained when the preparation was bathed in a Na+-containing external solution after K+ channel blockade with Cs+ in the pipette. Additional support was obtained by measurement of the volume of cells incubated in solutions containing 140 mM KCl. Tetr aethylammonium induced a bafilomycin-sensitive increase in inward K+ c urrent and an increase in cell volume of 76% which we believe to be a consequence of the K+ influx. Finally, comparison of membrane potentia ls obtained in experiments using Na+-containing external, and K+-conta ining pipette solutions and after K+ channel blockade with Cs+ in the pipette also showed that, under normal physiological conditions, the r esting membrane potential is essentially determined by an electrogenic H+ pump.