RELATIONS BETWEEN INTRACELLULAR IONS AND ENERGY-METABOLISM UNDER ACIDOTIC CONDITIONS - A STUDY WITH NIGERICIN IN SYNAPTOSOMES, NEURONS, ANDC6 GLIOMA-CELLS

Effects of nigericin were investigated in rat brain synaptosomes, cult ured neurons, and C6 glioma cells to characterize the relations among ATP synthesis, [Na+]i, [K+]i, and [Ca2+]i, and pH under conditions whe n [H+], is substantially increased and transmembrane electrical potent ial is decreased. Intracellular acidification and loss of K+ were acco mpanied by enhanced oxygen consumption and lactate production and a de crease in cellular energy level. Changes in the last three parameters were attenuated by addition of 1 mM ouabain. In synaptosomes treated w ith nigericin, neither respiration nor glycolysis was affected by 0.3 muM tetrodotoxin, whereas 1 mM amiloride reduced lactate production by 20% but did not influence respiration. In C6 cells, amiloride decreas ed the nigericin-stimulated rate of lactate generation by about 50%. T he enhancement by nigericin of synaptosomal oxygen uptake and glycolyt ic rate decreased with time. However, there was only a small reduction in respiration and none in glycolysis in C6 cells. Measurements with ion-selective microelectrodes in neurons and C6 cells showed that nige ricin also caused a rise in [Ca2+]i and [Na+]i. The increase in [Na+]i in C6 cells was partially reversed by 1 mM amiloride. It is concluded that nigericin-induced loss of K+ and subsequent depolarization lead to an increase in Na+ influx and stimulation of the Na+/K+ pump with a consequent rise in energy utilization; that acidosis inhibits mitocho ndrial ATP production; that a rise in [H+] does not decrease glycolyti c rate when the energy state (a fall in [ATP] and rises in [ADP] and [ AMP]) is simultaneously reduced; that a fall in [K+]i depresses both o xidative phosphorylation and glycolysis; and that the nigericin-induce d alterations in ion levels and activities of energy-producing pathway s can explain some of the deleterious effects of ischemia and hypoxia.