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Regulation of Intracellular pH in Guinea Pig Cerebral Cortex Ex Vivo Studied by 31 P and 1 H Nuclear Magnetic Resonance Spectroscopy: Role of Extracellular Bicarbonate and Chloride
Author(s) -
Pirttilä TiinaR. M.,
Kauppinen Risto A.
Publication year - 1994
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.1994.62020656.x
Subject(s) - intracellular ph , bicarbonate , extracellular , chemistry , biophysics , intracellular , nuclear magnetic resonance spectroscopy , ex vivo , pi , in vivo , biochemistry , stereochemistry , in vitro , biology , microbiology and biotechnology , organic chemistry
The role of transmembrane processes that are dependent on external anions in the regulation of cerebral intracellular pH (pH i ), high‐energy metabolites, and lactate was investigated using 31 P and 1 H NMR spectroscopy in an ex vivo brain slice preparation. During oxygenated superfusion, removal of external HCO 3 − /CO 2 in the presence of Na + led to a sustained split of the inorganic phosphate (P i ) peak so that the pH i 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 HCO 3 − . The pH in the compartment with a higher pH i value returned to 7.29 ± 0.04 by 10.5 min of superfusion in a HCO 3 − ‐free medium, whereas the pH i 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 HCO 3 − caused alkalinization without split of the P i peak. Both treatments reduced the rate of pH i normalization following alkalinization. Simultaneous omission of external HCO 3 − and Na + did not inhibit alkalinization of the pH i following CO 2 exit. All these data show that the acid loading mechanism at neutral pH i is mediated by an Na + ‐independent anion transport. During severe hypoxia, pH i 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 HCO 3 − , 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 HCO 3 − ‐free medium supplemented with 1 m M amiloride, the pH i fell only to 6.94 ± 0.08 despite the lactate concentration of 18.9 ± 2.4 mmol/kg. Acidification caused by hypoxia was also small in the slice preparations superfused in the absence of both HCO 3 − and Cl − , as the pH i was 7.01 ± 0.12 at a lactate concentration of 24.5 ± 2.4 mmol/kg. These data indicate that apart from anaerobic glucose metabolism, separate acidifying mechanisms are functioning during hypoxia under these conditions. Recovery of phosphocreatine levels following reoxygenation was >75% relative to the prehypoxic level in the slice preparations superfused in the absence of HCO 3 − but <47% in those preparations superfused without HCO 3 − and Cl − . This indicates that either neutral pH i or absence of Cl − during hypoxia was deleterious to the energy metabolism. The present data indicate that Cl − /HCO 3 − exchange mechanisms have distinct roles in cerebral H + homeostasis depending on the level of pH i and energy state.