흰쥐 해마 (hippocampus)에서 acetylcholine(ACh) 유리에 미치는 adenosine 및 이에 미치는 magnesium의 역할에 관한 지견을 얻고자하여 [3H]-choline으로 평형시킨 해마 slice를 사용하여 [3H]-ACh 유리에 미치는 여러가지 약물들의 영향을 관찰하였다. Adenosine *0.3 ~ 100μM)은 전기자극 (3 Hz, 5 Vcm-1, 2 ms, rectangular pulses)에 의한 [3H]-ACh 유리를 용량 의존적으로 감소시켰다. A1-adenosine 수용체 차단제인 8-cyclopentyl-1, 3-dipropylxanthine (DPCPX, 1-10μM)은 용량 의존적으로 [3H]-ACh 유리를 증가시켰으며, adenosine과 2μM DPCPX 동시 투여시 adenosine의 효과가 억제됨을 볼 수 있었다. A2-수용체 흥분제인 5-(N-cyclopropyl)-carboxamidoadenosine (CPCA, 0.3 ~ 30μM)은 자극에 의한 [3H]-ACh 유리를 용량 의존적으로 감소시켰으며, 이 역시 2μM DPCPX 동시 투여시 그 효과가 차단됨을 관찰할 수 있었다. 그러나 또다른 A2-흥분약인 CGS 21680C는 [3H]-ACh 유리에 별다른 영향을 미치지 못하였다. 한편 관류액내의 magnesium 농도를 변화시켰을때 magnesium 그 자체로는 [3H]-ACh 유리에 별다른 변화가 없었으며, magnesium을 4 mM로 증가시켰을때 adenosine의 효과가 크게 강화되어 용량 반응 곡선이 좌측으로 이동됨을 볼 수 있었다. 이상의 실험 결과로 adenosine은 흰쥐 해마의 choline 작동성 신경에 presynaptic A1-adenosine heteroreceptor를 통하여 ACh 유리 감소를 일으키며, 이러한 adenosine 작용은 magnesium이온에 의존적임을 알 수 있었다.
As it has been reported that the depolarization-induced ACh release is modulated by activation of presynaptic A1-adenosine heteroreceptor in hippocampus and various lines of evidence indicate the adenosine effect is magnesium dependent, the present study was undertaken to delineate the role of endogenus adenosine as a modulator of hippocampal acetylcholine release in this study. Slices from the rat hippocampus were equilibrated with [3H]-choline and the release of the labelled product, [3H]-ACh, was evoked by electrical stimulation(3Hz, 5 V cm-1, 2ms, rectangular pulses), and the influence of various agents on the evoked tritium outflow was investigated. Adenosine, in concentrations ranging from 0.3 to 100μM, decreased the [3H]-ACh release in a dose-dependent manner without changing the basal rate of release. DPCPX(1 ~ 10μM), a selective A1-receptor antagonist, increased the [3H]-ACh release in a dose-related fashion with slight increase of basal tritium release. And the effects of adenosine were significantly inhibited by DPCPX(2μM) treatment. CPCA, a specific A2-agonist, in concentration ranging from 0.3 to 30μM decreased evoked tritium outflow with increase of basal rate of tritium release, and these effects were also abolished by DPCPX(2μM) pretreatment. But, CGS(0.1 ~ 10μM), a recently introduced potent A2-agonist, did not alter the evoked tritium outflow. When the magnesium concentration of the medium was reduced to 0 mM, there was no change in evoked ACh release by adenosine. In contrast, increasing the magnesium concentration to 4 mM, the inhibitory effects of adenosine were significantly potentiated. These results indicate that A1-adenosine heteroreceptor is involved in ACh-release in the rat hippocampus and the inhibitory effects of adenosine mediated by A1-receptor is magnesium-dependent.
