Magnesium and zinc potentiate ethanol inhibition of N-methyl-D-aspartate-stimulated nitric oxide synthase in cortical neurons
Chandler, L.J.; Guzman, N.J.; Sumners, C.; Crews, F.T.
Journal of Pharmacology and Experimental Therapeutics 271(1): 67-75
1994
ISSN/ISBN: 0022-3565 PMID: 7525932 Document Number: 438192
The coupling of calcium mobilizing receptors to nitric oxide (NO) formation was examined in cerebral cortical cultures. Of the various agents tested, only glutamate, depolarization with KCl and the calcium ionophore ionomycin stimulated nitric oxide synthase (NOS) activity. Characterization of the glutamate response revealed that the ionotropic glutamate receptor agonists N-methyl-D-aspartate (NMDA), kainate and alpha-amino-3-hydroxy-5-methyl-4-isoxalone propionic all stimulated NOS activity with a relative maximal efficacy of NMDA gt kainate gt alpha-amino-3-hydroxy-5-methyl-4-isoxalone propionic. Ethanol, Mg++ and Zn++ produced a concentration-dependent inhibition of NMDA stimulation of NOS. The Mg++ inhibition was reversed by increasing concentrations of NMDA, whereas Zn-2+ inhibition was not. Ethanol (100 mM) produced an apparent competitive type inhibition as seen by a parallel right-shift in the NMDA concentration-response curve. However, ethanol inhibition was dependent upon the presence of Mg-2+ and/or Zn++ in a concentration-related manner. Whereas 100 mM ethanol did not significantly inhibit NMDA stimulation of NOS activity in the absence of Mg-2+ and Zn++, inclusion of a combination of these cations increased the sensitivity to ethanol such that the NMDA response was completely blocked by 100 mM ethanol (IC-50 apprx 30 mM). The potency for inhibition of NMDA stimulation of NOS by several short-chain alcohols followed, their hydrophobicity profile and showed a similar dependency upon Mg++ for inhibition. alpha-amino-3-hydroxy-5-methyl-4-isoxalone propionic, but not kainate, stimulation of NOS was also inhibited by ethanol (100 mM). These results indicate that activation of NOS in cultured cerebral cortical neurons occurs primarily through ionotropic glutamate receptors that show a differential sensitivity to ethanol inhibition. Ethanol appears to act in an interactive manner with Mg++ and Zn++ ions to inhibit NMDA receptors that couple to stimulation of NOS by potentiating the blocking actions of these cations.