Interaction of pitrazepin with the GABA/benzodiazepine receptor complex and with glycine receptors

Pitrazepin (3-(piperazinyl-1)-9H-dibenz(c,f)triazolo(4,5-a)azepin) is a new GABAA receptor antagonist reported to antagonize electrophysiological effects of GABA. We have investigated in some detail the interaction of pitrazepin with the GABA/benzodiazepine receptor chloride channel complex. Pitrazepin was found to be a competitive inhibitor of the GABAA receptor which is coupled to [3H]diazepam and [35S]TBPS binding sites; the KI value obtained by Schild analyses was 80 nM. Although pitrazepin interacted weakly with BZ receptors the compound did not affect the chloride gating mechanism (labelled with [35S]TBPS or [3H]avermectin B1a). Further, pitrazepin was a non-selective GABA antagonist since glycine receptors, labelled with [3H]strychnine, were affected at low concentrations (the KI values in rat brain-stem were 71-110 nM).