Effects of
nigericin were investigated in rat brain synaptosomes, cultured neurons, and C6
glioma cells to characterize the relations among
ATP synthesis, [Na+]i, [K+]i, and [Ca2+]i, and pH under conditions when [H+]i is substantially increased and transmembrane electrical potential is decreased. Intracellular acidification and loss of K+ were accompanied by enhanced oxygen consumption and
lactate production and a decrease in cellular energy level. Changes in the last three parameters were attenuated by addition of 1 mM
ouabain. In synaptosomes treated with
nigericin, neither respiration nor glycolysis was affected by 0.3 microM
tetrodotoxin, whereas 1 mM
amiloride reduced
lactate production by 20% but did not influence respiration. In C6 cells,
amiloride decreased the
nigericin-stimulated rate of
lactate generation by about 50%. The enhancement by
nigericin of synaptosomal
oxygen uptake and glycolytic 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
nigericin 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 mitochondrial
ATP production; that a rise in [H+] does not decrease glycolytic 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 oxidative phosphorylation and glycolysis; and that the
nigericin-induced alterations in ion levels and activities of energy-producing pathways can explain some of the deleterious effects of
ischemia and
hypoxia.