"Run-down" of gamma-aminobutyric acidA receptor function during whole-cell recording: a possible role for phosphorylation.

When using whole-cell recording methods and a minimal intracellular medium containing only inorganic ions, ethyleneglycolbis-(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid, and N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid, we have observed a time-dependent decrease in the responsiveness of cultured chick spinal cord neurons to gamma-aminobutyric acid (GABA). The current evoked by 30 microM GABA progressively declined to approximately 30% of its initial value after five applications at 10-min intervals. This was accompanied by an equivalent decline in the GABA-evoked membrane conductance. "Run-down" of the response was reduced when Mg2+-ATP was present in the pipet solution. Inclusion of ATP-gamma-S, an analog that donates a thiophosphate group resistant to hydrolysis, also reduced run-down. The nonhydrolyzable analog beta, gamma-imidoadenosine-5'-triphosphate was without effect. These results suggest that an ATP-dependent process, possibly phosphorylation, is involved in the maintenance of GABAA receptor function.