Effects of the arylaminopyridazine-GABA derivatives, sr95103 and SR95531 on the Ascaris muscle GABA receptor: the relative potency of the antagonists in Ascaris is different to that at vertebrate GAB A, receptors

Abstract

1. GABA-induced changes in input conductance in the bag region of Ascaris suum muscle were monitored using a two-microelectrode current-clamp technique. 2. Effects of the arylaminopyridazine-GABA derivatives, SR95103 and SR95531 on GABA conductance responses were observed. 3. SR95103 was more potent than SR95531 as an antagonist; this potency order contrasts with vertebrate GABA, receptors. 4. The antagonism of SR95103 was associated with a parallel shift to the right in the GABA dose-response relationships. 5. A modified Schild plot was used to describe the action of SR95103: the data was consistent with 2 molecules of GABA but one molecule of antagonist interacting with the receptor. 6. The K B for SR95103 was 64 ± 13 μM (mean ± SE, N = 14).