Regulation of intracellular pH in guinea pig cerebral cortex ex vivo studied by 31P and 1H nuclear magnetic resonance spectroscopy: role of extracellular bicarbonate and chloride.

The role of transmembrane processes that are dependent on external anions in the regulation of cerebral intracellular pH (pHi), high-energy metabolites, and lactate was investigated using 31P and 1H NMR spectroscopy in an ex vivo brain slice preparation. During oxygenated superfusion, removal of external HCO3-/CO2 in the presence of Na+ led to a sustained split of the inorganic phosphate (Pi) peak so that the pHi indicated by one part of the peak was 0.38 pH units more alkaline and by the other part 0.10 pH units more acidic at 5 min than in the presence of HCO3-. The pH in the compartment with a higher pHi value returned to 7.29 +/- 0.04 by 10.5 min of superfusion in a HCO3(-)-free medium, whereas the pHi in an acidic compartment was reduced to 7.02. In the presence of 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid or the absence of external Cl-, removal of HCO3- caused alkalinization without split of the Pi peak. Both treatments reduced the rate of pHi normalization following alkalinization. Simultaneous omission of external HCO3- and Na+ did not inhibit alkalinization of the pHi following CO2 exit. All these data show that the acid loading mechanism at neutral pHi is mediated by an Na(+)-independent anion transport. During severe hypoxia, pHi dropped from 7.29 +/- 0.05 to 6.13 +/- 0.16 and from 7.33 +/- 0.03 to 6.67 +/- 0.05 in the absence and presence of HCO3-, respectively, in Na(+)-containing medium. Lactate accumulated to 18.7 +/- 2.8 and 19.6 +/- 1.5 mmol/kg under the respective conditions. In the HCO3(-)-free medium supplemented with 1 mM amiloride, the pHi fell only to 6.94 +/- 0.08 despite the lactate concentration of 18.9 +/- 2.4 mmol/kg.(ABSTRACT TRUNCATED AT 250 WORDS)