Selective effects of enzyme treatment used for dissociating single cells on their GABA-receptor activities

Frog dorsal root ganglion (DRG) cells treated with collagenase and trypsin were dissociated mechanically. The characteristics of dose-response curves of GABA-induced Cl- currents (ICl) were mainly studied using the "concentration-clamp" technique, by which the external solution around isolated single neurons was rapidly changed within a few milliseconds. The saturating maximum currents induced by various concentrations of GABA normalized to the peak ICl induced by 10(-5) M GABA on the same neuron varied from 1.5 to 5.5 among the neurons, though the absolute maximum currents varied little. The Hill coefficients (n = 1.92 +/- 0.09, mean +/- S.D.) also varied little on the neurons. The time constants of the desensitization phase of fully activated GABA responses were not so markedly different among the neurons. The present results suggested a possibility that the enzyme treatment produced a selective inactivation of alpha 1 unit, a high affinity subtype of the GABA-receptor.