Changing cation levels (Mg2+, Ca2+, Na+) alters the release of glutamate, GABA and other substances from the guinea pig cochlea.
We examined the effects of changes in cation levels (increased Mg2+ concentration combined with low Ca2+ concentration, and two low concentrations of Na+) on the perilymph levels of gamma-aminobutyric acid (GABA), glutamate (Glu), aspartate (Asp) and other substances. Artificial perilymph solutions containing normal (5 mM) and high (50 mM) levels of K+ were perfused through the perilymphatic compartment of the guinea pig cochlea to examine basal release (5 mM K+) and depolarization-induced release (50 mM K+). Each of the two K+ concentrations were contained in four different solutions: [I] normal artificial perilymph (NARP; NaCl, 137 mM; CaCl2, 2 mM; MgCl2, 1 mM;); [II] high Mg2+ (20 mM)/low Ca2+ (0.1 mM) (HMgLCa); [III] low Na+ (117 mM; LNa), and [IV] very low Na+ (NaCl, 0 mM; VLNa). The effluent was collected and assayed for eighteen primary amines by HPLC. Compared with NARP, the HMgLCa group had an increase in the high K(+)-induced release of Asp and Glu with no change in GABA. VLNa increased the normal K+ levels of Asp, Glu and GABA up to those observed with high K+ in NARP. VLNa increased the high K+ levels of Asp and Glu over fivefold compared with the high K+ levels in NARP, but decreased GABA. We ascribe the results to an interference with either a Na(+)-dependent uptake processes or a Na+/Ca2+ exchange carrier.
Kresge Hearing Research Laboratory of the South, Louisiana State University Medical Center, New Orleans 70112-2234.
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D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D003051:Cochlea / Q000187:drug effects / Q000378:metabolism*; D005260:Female; D005971:Glutamates / Q000378:metabolism*; D018698:Glutamic Acid; D006168:Guinea Pigs; D008274:Magnesium / Q000494:pharmacology; D008297:Male; D010498:Perilymph / Q000378:metabolism; D011188:Potassium / Q000494:pharmacology; D012964:Sodium / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D000596:Amino Acids; D005971:Glutamates; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid; D012964:Sodium; D008274:Magnesium; D011188:Potassium; D002118:Calcium