흰쥐 해마(hippocampus)에서 acetylcholine(Ach) 유리에 미치는 A1-adenosine 수용체의 역할과 post-receptor 기전에 있어서 adenylate cyclase 계의 관여여부에 관한 지견을 얻고자 하여 [3H]-choline으로 평형시킨 해마 slice를 사용하여 [3H]-ACh 유리에 미치는 여러가지 약물들의 영향을 관찰하였다. A1-adenosine 수용체 흥분제인 N6-cyclopentyladenosine(CPA, 0.1 ~ 10μM)은 전기자극(3Hz, 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, 이때 기저(basal)유리 또한 증가됨을 관찰할 수 있었고, 2μM DPCPX 전처리는 CPA의 효과를 길항하여 CPA에 의한 용량반응곡선을 우측으로 이동시킴을 볼 수 있었다. G protein 억제제인 N-ethylmaleimide(NEM, 10 & 30μM)는 그 자체에 의하여 자극에 의한 ACh 유리를 증가시켰으며, 기저유리 또한 증가함을 볼 수 있었다. NEM 전처리에 의하여 CPA의 효과는 완전히 소실되었다. 한편 adenylate cyclase 활성화제인 forskolin(0.3 ~ 10μM)은 기저유리에 변함없이 용량의존적인 [3H]-ACh 유리의 증가를 초래하였으며 3μM forskolin 전처리는 대량(10μM)의 CPA의 효과를 제외하고는 CPA의 효과를 억제시킴을 관찰할 수 있었다. 이상의 실험 결과로 흰쥐 해마의 choline 작동성신경의 presynaptic A1-adenosine heteroreceptor는 ACh 유리에 중요한 역할을 하고 있으며, ACh 유리의 조절에 Gi-단백질을 통한 adenylate cyclase 계의 관여가 확실하다 하겠다.
As it has been reported that the depolarization-induced acetylcholine (ACh) release is modulated by activation of presynaptic A1-adenosine heteroreceptor in hippocampus and various lines of evidence indicate the involvement of adenylate cyclase system in A1-adenosine post-receptor mechanism in hippocampus, it was attempted to delineate the role of adenylate cyclase system in the A1-receptor-mediated control of ACh release in this study. Slices from rat hippocampus were incubated with [3H]-choline and the release of the labelled products was evoked by electrical stimulation (3 Hz, 5 Vcm-1, 2 ms, rectangular pulses), and the influence of various agents on the evoked tritium-outflow was investigated. N6-cyclopentyladenosine (CPA), a specific A1-adenosine receptor agonist, in concentrations ranging from 0.1 to 10μM, decreased the [3H]-ACh release in a dose-dependent manner without the changes of basal rate of release. 8-cyclopentyl-1,3-dipropylxanthine (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 CPA effects were significantly inhibited by DPCPX (2μM) pretreatment and the dose-response curve produced by CPA was shifted to the right. The responses to N-ethylmaleimide (NEM, 10 & 30μM), a SH-alkylating agent of G-protein, were characterized by increments of the evoked ACh-release and the basal release, and the CPA effect were completely abolished by NEM pretreatment. Forskolin, a specific adenylate cyclase activator, in concentrations ranging from 0.3 to 10μM, increased the evoked ACh-release in a dose-dependent manner and the CPA effects were inhibited by forskolin. These results indicate that the A1-adenosine heteroreceptor plays an important role in ACh-release via nucleotide-binding protein Gi in the rat hippocampus and that the adenylate cyclase system might be participated in this process.
