RELATIONS BETWEEN INTRACELLULAR IONS AND ENERGY-METABOLISM UNDER ACIDOTIC CONDITIONS - A STUDY WITH NIGERICIN IN SYNAPTOSOMES, NEURONS, ANDC6 GLIOMA-CELLS
M. Erecinska et al., RELATIONS BETWEEN INTRACELLULAR IONS AND ENERGY-METABOLISM UNDER ACIDOTIC CONDITIONS - A STUDY WITH NIGERICIN IN SYNAPTOSOMES, NEURONS, ANDC6 GLIOMA-CELLS, Journal of neurochemistry, 61(4), 1993, pp. 1356-1368
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.