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Nuclear Magnetic Resonance Studies on the Effects of Decreased External Sodium on Guinea Pig Cerebral Cortex Slices and the Permeabilities of Various Sodium Substitutes
Author(s) -
Brooks K. J.,
Bachelard H. S.
Publication year - 1992
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 - 10.1111/j.1471-4159.1992.tb08447.x
Subject(s) - tetramethylammonium , chemistry , choline , sodium , phosphocreatine , tris , sucrose , potassium , nuclear magnetic resonance spectroscopy , intracellular ph , analytical chemistry (journal) , choline chloride , nuclear chemistry , nuclear magnetic resonance , intracellular , biochemistry , chromatography , medicine , stereochemistry , ion , physics , organic chemistry , energy metabolism
Decreasing the external sodium concentration ([Na + ] e ) to 10 m M in the presence of 280 m M sucrose had no significant effect on phosphocreatine (PCr) or on intracellular pH (pH i ) as assessed using 31 P nuclear magnetic resonance spectroscopy. Zero [Na + ] e in the presence of 300 m M sucrose caused a fall in PCr levels to 50% of control values, and the pH i fell to 6.85 from a control value of 7.30. 1 H nuclear magnetic resonance spectroscopy confirmed that the sucrose had not entered the tissue. The decreases in PCr content and in pH i , known to occur on depolarization using 40 m M external potassium concentration ([K + ] c ), were further decreased in the presence of 10 m M [Na + ] e , to 51.4 ± 4.0 and 6.80 ± 0.10% of control values, respectively. The free intracellular magnesium concentration was significantly increased from a control value of 0.37 ± 0.10 m M to 0.66 ±0.13 m M ( p < 0.001), when [Na + ] e was decreased to 10 m M , but was not further affected by high [K + ] e or zero Na + . Membrane permeabilities of the sodium substitutes N ‐methyl‐D‐glucamine (NMG), tris(hydroxymethyl)aminomethane (Tris), tetramethylammonium (TMA), and choline were assessed using 1 H nuclear magnetic resonance spectroscopy. In the presence of 10 m M [Na + ] e , NMG, TMA, and choline (all at 140 m M ) were taken up and remained within the tissue for at least 2 h, but no uptake of Tris (140 m M ) or sucrose (above) could be detected. Tissue lactate levels (from the lactate/ N ‐acetyl aspartate ratio) increased in the presence of the substitutes that were taken up, although no change in pH was detected.