Mechanism of Inhibition of N-Methyl-d-Aspartate-Stimulated Increases in Free Intracellular Ca2+ Concentration by Ethanol

Dissociated brain cells were isolated from newborn rat pups and loaded with fura-2. These cells were sensitive to low N-methyl-D-aspartate (NMDA) concentrations with EC50 values for NMDA-induced intracellular Ca2+ concentration (Ca2+]i) increases of approximately 7-16 microM measured in the absence of Mg2+. NMDA-stimulated Ca2+]i increases could be observed in buffer with Mg2+ when the cells were predepolarized with 15 mM KCl prior to NMDA addition. Under these predepolarized conditions, 100 mM ethanol inhibited 25 microM NMDA responses by approximately 50%, which was similar to the ethanol inhibition observed in buffer without added Mg2+. Ethanol did not alter Ca2+]i prior to NMDA addition. In the absence of Mg2+, 50 and 100 mM ethanol did not significantly alter the EC50 value for NMDA, but did inhibit NMDA-induced increases in Ca2+]i in a concentration-dependent manner at 4, 16, 64, and 256 microM NMDA. Whereas NMDA-induced increases in Ca2+]i were dependent on extracellular Ca2+ and were inhibited by Mg2+, the ability of 100 mM ethanol to inhibit 25 microM NMDA responses was independent of the external Ca2+ or Mg2+ concentrations. Glycine (1, 10, and 100 microM) enhanced 25 microM NMDA-induced increases in Ca2+]i by approximately 50%. Glycine (1-100 microM) prevented the 100 mM ethanol inhibition of NMDA-stimulated Ca2+]i observed in the absence of exogenous glycine. MK-801 (25-400 nM) inhibited 25 microM NMDA-stimulated rises in Ca2+]i in a concentration-dependent manner.(ABSTRACT TRUNCATED AT 250 WORDS)