Adenosine receptor antagonists alter the stability of human epileptic [GABA.sub.A] receptors

We examined how the endogenous anticonvulsant adenosine might influence [gamma]-aminobutyric acid type A ([GABA.sub.A]) receptor stability and which adenosine receptors (ARs) were involved. Upon repetitive activation (GABA 500 [micro]M), [GABA.sub.A] receptors, microtransplanted into Xenopus oocytes from neurosurgically resected epileptic human nervous tissues, exhibited an obvious [GABA.sub.A]-current ([I.sub.GABA]) run-down, which was consistently and significantly reduced by treatment with the nonselective adenosine receptor antagonist CGS15943 (100 nM) or with adenosine deaminase (ADA) (1 units/ ml), that inactivates adenosine. It was also found that selective antagonists of A2B (MRS1706, 10 nM) or A3 (MRS1334, 30 nM) receptors reduced [I.sub.GABA] run-down, whereas treatment with the specific A1 receptor antagonist DPCPX (10 nM) was ineffective. The selective A2A receptor antagonist SCH58261 (10 nM) reduced or potentiated [I.sub.GABA] run-down in [approximately equal to]40% and [approximately equal to]20% of tested oocytes, respectively. The ADA-resistant, AR agonist 2-chloroadenosine (2-CA) (10 [micro]M) potentiated [I.sub.GABA] run-down but only in [approximately equal to]20% of tested oocytes. CGS15943 administration again decreased [I.sub.GABA] run-down in patch-clamped neurons from either human or rat neocortex slices. [I.sub.GABA] run-down in pyramidal neurons was equivalent in A1 receptor-deficient and wt neurons but much larger in neurons from A2A receptor-deficient mice, indicating that, in mouse cortex, [GABA.sub.A]-receptor stability is tonically influenced by A2A but not by A1 receptors. [I.sub.GABA] run-down from wt mice was not affected by 2-CA, suggesting maximal ARs activity by endogenous adenosine. Our findings strongly suggest that cortical A2-A3 receptors alter the stability of [GABA.sub.A] receptors, which could offer therapeutic opportunities. A2A receptor | A3 receptor | microtransplantation into Xenopus oocyte | temporal lobe epilepsy