Intracellular pH (pH(i)) is an important factor for understanding cellular processes associated with the response of central neurons to metabolic disturbances such as
anoxia or
ischemia. In the present study, pH(i) was fluorometrically measured in 2'7'-bis(carboxyethyl)-5(6)-carboxyfluorescin (
BCECF)-filled, voltage-clamped dorsal vagal neurons (DVN) of brainstem slices from rats during metabolic disturbances activating
ATP-sensitive K(+) (K(
ATP)) channels. Chemical
anoxia induced by
cyanide,
rotenone or p-trifluoromethoxy-
phenylhydrazone (
FCCP) decreased pH(i) by >0.4 pH units. Untreated neurons with normal pH(i) baseline (7.2) responded to
glucose-free superfusate after a delay of 7-16 min with a progressive fall of pH(i). In contrast, pH(i) increased by >0.2 pH units after approximately 10 min in cells that had a mean pH(i) of 6.8 due to incomplete recovery from a CN(-)induced
acid load prior to
glucose depletion. Metabolic arrest, induced by
cyanide in
glucose-free
solution after 30 min preincubation in
glucose-free saline, caused a progressive
glutamate-mediated inward current with no change of pH(i). Upon metabolic arrest, depolarization-evoked pH(i) decreases ( approximately 0.2 pH units) were abolished, whereas
glucose-free superfusate slightly delayed their recovery without major effects on amplitude. The
glucose-dependent pH(i) fall coincided with activation of the K(
ATP) channel-mediated outward current, while K(
ATP) currents due to
anoxia or metabolic arrest could reach their maximum in the absence of a major pH(i) change. The results indicate that the anoxic pH(i) decrease is due to enhanced glycolysis and
lactate formation with often no obvious effect on K(
ATP) channel activity. The origin of
glucose-dependent
acidosis and its relation to K(
ATP) channel activity remain to be determined.