The human GABA(B1b) and GABA(B2) heterodimeric recombinant receptor shows low sensitivity to phaclofen and saclofen.

1. The aim of this study was to characterize the pharmacological profile of the GABA(B1)/GABA(B2) heterodimeric receptor expressed in Chinese hamster ovary (CHO) cells. We have compared receptor binding affinity and functional activity for a series of agonists and antagonists. 2. The chimeric G-protein, G(qi5), was used to couple receptor activation to increases in intracellular calcium for functional studies on the Fluorimetric Imaging Plate Reader (FLIPR), using a stable GABA(B1)/GABA(B2)/G(qi5) CHO cell line. [(3)H]-CGP-54626 was used in radioligand binding studies in membranes prepared from the same cell line. 3. The pharmacological profile of the recombinant GABA(B1/B2) receptor was consistent with that of native GABA(B) receptors in that it was activated by GABA and baclofen and inhibited by CGP-54626A and SCH 50911. 4. Unlike native receptors, the GABA(B1)/GABA(B2)/G(qi5) response was not inhibited by high microMolar concentration of phaclofen, saclofen or CGP 35348. 5. This raises the possibility that the GABA(B1)/GABA(B2)/G(qi5) recombinant receptor may represent the previously described GABA(B) receptor subtype which is relatively resistant to inhibition by phaclofen.

Functional comparison of muscarinic partial agonists at muscarinic receptor subtypes hM1, hM2, hM3, hM4 and hM5 using microphysiometry.

1. This study describes the pharmacological comparison of the muscarinic partial agonists sabcomeline, xanomeline and milameline at human cloned muscarinic receptor subtypes (hM1-5). 2. Radioligand binding studies at the hM1-5 muscarinic receptor subtypes were compared with functional studies using microphysiometry using carbachol as the standard full agonist. 3. In binding assays none of the compounds studied displayed preferential affinity for the M1,3,4 or M5 subtypes although carbachol was less potent at hM1 than hM3,4,5. 4. In functional studies, all of the compounds studied displayed similar levels of efficacy across the muscarinic receptors with the exception of M3, where there was a large apparent receptor reserve and the compounds behaved essentially as full agonists. 5. Sabcomeline was the most potent agonist in functional studies but also showed the lowest efficacy. In terms of potency, xanomeline showed some selectivity for M1 over M2 receptors and milameline showed some selectivity for M2 over M1 receptors. 6. These results show the value of microphysiometry in being able to compare receptor pharmacology across subtypes irrespective of the signal transduction pathway. 7. None of the partial agonists showed functional selectivity for M1 receptors, or indeed any muscarinic receptor, in the present study.

The effects of SB 206284A, a novel neuronal calcium-channel antagonist, in models of cerebral ischemia.

The effects of SB 206284A, 1-[7-(4-benzyloxyphenoxy)heptyl] piperidine hydrochloride, have been investigated in vitro on calcium and sodium currents in rat-cultured dorsal root ganglion (DRG) neurones and potassium-mediated calcium influx in rat synaptosomes. Cardiovascular hemodynamic effects in both anesthetized and conscious rats, and neuroprotective activity in in vivo cerebral ischemia models were also investigated. In the rat DRG cells, SB 206284A caused almost complete block of the sustained inward Ca2+ current (IC50 = 2.4 microM), suggesting that the compound is an effective blocker of slowly inactivating, high-voltage calcium current. SB 206284A reduced locomotor hyperactivity in the gerbil bilateral carotid artery occlusion model without affecting ischemia-induced damage in the hippocampal CA1 region. In the rat middle cerebral artery occlusion model, SB 206284A reduced lesion volume in the posterior forebrain, and in the rat photochemical cortical lesion model, lesion volume was reduced even when treatment was delayed until 4 hours after occlusion. At neuroprotective doses, SB 206284A had no cardiovascular effects. These findings show that SB 206284A is a novel calcium channel antagonist that shows neuroprotective properties.

SB 201823-A, a neuronal Ca2+ antagonist is neuroprotective in two models of cerebral ischaemia.

We have characterised the Ca2+ channel blocking properties of a new non-peptide Ca2+ channel antagonist, SB 201823-A, in cultures of rat sensory neurones. The IC50 for SB 201823-A against total Ca2+ current in sensory neurones was 4.9 microM. SB 201823-A showed little selectivity for sub-types of neuronal Ca2+ channel but was selective for Ca2+ channels over Na+ and K+ channels. Efficacy against other types of cation channel such as agonist gated channels was not assessed. SB 201823-A was neuroprotective in vivo when administered post-ischaemia in one focal and one global model of neuronal ischaemia. In the rat photothrombotic focal lesion model, SB 201823-A administered i.p. 10 min post-ischaemia resulted in a dramatic reduction in lesion volume. In the gerbil bilateral carotid artery occlusion global model, SB 201823-A dosed i.p. 30 min post-occlusion resulted in both histological and functional improvements when compared to vehicle treated animals. These data suggest that such novel neuronal Ca2+ channel antagonists may have potential in ameliorating both the pathological and functional consequences of stroke in man.