Intracellular pH and KATP channel activity in dorsal vagal neurons of juvenile rats in situ during metabolic disturbances

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.