Effects of chronic ethanol treatment on gamma-aminobutyric acid(A) and glycine receptors in mouse glycinergic spinal neurons.

Five-day-old cultures of mouse glycinergic spinal interneurons were chronically treated with 100 mM ethanol and the glycine and gamma-aminobutyric acid (GABA)(A) receptors were assayed using whole-cell recordings and fluorescence-imaging techniques. Control neurons displayed a glycine(50) of 19 +/- 0.6 microM and a Hill coefficient of 3.1 +/- 0.3. Chronic ethanol treatment did not significantly change these parameters. The maximal responses were 310 +/- 80 pA/pF in control and 440 +/- 19 pA/pF in treated cells, and the fluorescence intensity associated to a monoclonal glycine receptor antibody was unchanged. Strychnine inhibited the glycine current with smaller potency (29%) in treated neurons, thus the IC(50) increased from 14 +/- 2 nM in control to 18 +/- 6 nM in treated neurons. Zn(2+) (10 microM) potentiated the glycine current by 43 +/- 33% in control, but only by 18 +/- 13% in treated neurons. Interestingly, no change on the inhibition produced by a high concentration of Zn(2+) was found in treated neurons. The inhibitory effect of picrotoxin on the glycine receptor, associated to a homomeric receptor, was eliminated with chronic ethanol, suggesting a faster switch to beta-subunit-containing receptors. Unlike glycine receptors, the sensitivity of GABA(A) receptors to GABA, pentobarbital, diazepam, and Zn(2+), as well as the fluorescence intensity associated to a high-affinity benzodiazepine analog was unchanged by chronic ethanol. In conclusion, we found that glycine receptors in spinal interneurons were altered by chronic ethanol treatment and this may reflect the expression of different subunits in control and treated neurons. GABA(A) receptors were resistant to the treatment.