1 TRPM2 (melastatin-like transient receptor potential 2 channel) is a nonselective cation channel that is activated under conditions of oxidative stress leading to an increase in intracellular free Ca 27; 6.3570.18; 5.2970.12, respectively). The order of potency of the PARP inhibitors in these assays (SB7501394PJ344DPQ) was the same as for inhibition of isolated PARP enzyme. 4 SB750139-B, PJ34 and DPQ had no effect on inward currents elicited by intracellular ADP-ribose in tetracycline-induced TRPM2-HEK293 cells, suggesting that PARP inhibitors are not interacting directly with the channel. 5 SB750139-B, PJ34 and DPQ inhibited increases in [Ca 2 þ ] i in a rat insulinoma cell line (CRI-G1 cells) endogenously expressing TRPM2 (pIC 50 vs 100 mM H 2 O 2 : 7.6470.38; 6.6870.28; 4.7870.05, respectively). 6 These data suggest that oxidative stress causes TRPM2 channel opening in both recombinant and endogenously expressing cell systems via activation of PARP enzymes.

Amyloid b-peptide (Ab) is the main component of senile plaques which characterize Alzheimer's disease and may induce neuronal death through mechanisms which include oxidative stress. To date, the signalling pathways linking oxidant stress, a component of several neurodegenerative diseases, to cell death in the CNS are poorly understood. Melastatin-like transient receptor potential 2 (TRPM2) is a Ca 2+ -permeant non-selective cation channel, which responds to increases in oxidative stress levels in the cell and is activated by oxidants such as hydrogen peroxide. We demonstrate here that Ab and hydrogen peroxide both induce death in cultured rat striatal cells which express TRPM2 endogenously. Transfection with a splice variant that acts as a dominant negative blocker of TRPM2 function (TRPM2-S) inhibited both hydrogen perox-

GABA B receptors are G-protein-coupled receptors that mediate slow synaptic inhibition in the brain and spinal cord. These receptors are heterodimers assembled from GABA B1 and GABA B2 subunits, neither of which is capable of producing functional GABA B receptors on homomeric expression. GABA B1, although able to bind GABA, is retained within the endoplasmic reticulum (ER) when expressed alone. In contrast, GABA B2 is able to access the cell surface when expressed alone but does not couple efficiently to the appropriate effector systems or produce any detectable GABA-binding sites. In the present study, we have constructed chimeric and truncated GABA B1 and GABA B2 subunits to explore further GABA B receptor signaling and assembly. Removal of the entire C-terminal intracellular domain of GABA B1 results in plasma membrane expression without the production of a functional GABA B receptor. However, coexpression of this truncated GABA B1 subunit with either GABA B2 or a truncated GABA B2 subunit in which the C terminal has also been removed is capable of functional signaling via G-proteins. In contrast, transferring the entire C-terminal tail of GABA B1 to GABA B2 leads to the ER retention of the GABA B2 subunit when expressed alone. These results indicate that the C terminal of GABA B1 mediates the ER retention of this protein and that neither of the C-terminal tails of GABA B1 or GABA B2 is an absolute requirement for functional coupling of heteromeric receptors. Furthermore although GABA B1 is capable of producing GABA-binding sites, GABA B2 is of central importance in the functional coupling of heteromeric GABA B receptors to G-proteins and the subsequent activation of effector systems.

A selective dopamine D(3) receptor antagonist offers the potential for an effective antipsychotic therapy, free of the serious side effects of currently available drugs. Using clearance and brain penetration studies as a screen, a series of 1,2,3, 4-tetrahydroisoquinolines, exemplified by 13, was identified with high D(3) affinity and selectivity against the D(2) receptor. Following examination of molecular models, the flexible butyl linker present in 13 was replaced by a more conformationally constrained cyclohexylethyl linker, leading to compounds with improved oral bioavailability and selectivity over other receptors. Subsequent optimization of this new series to improve the cytochrome P450 inhibitory profile and CNS penetration gave trans-N-[4-[2-(6-cyano-1, 2,3, 4-tetrahydroisoquinolin-2-yl)ethyl]cyclohexyl]-4-quinolinecarbo xamide (24, SB-277011). This compound is a potent and selective dopamine D(3) receptor antagonist with high oral bioavailability and brain penetration in the rat and represents an excellent new chemical tool for the investigation of the role of the dopamine D(3) receptor in the CNS.