Chen G, van den Pol A N
Section of Neurosurgery, Yale University School of Medicine, New Haven, Connecticut 06520, USA.
J Neurophysiol. 1997 Jun;77(6):3035-47. doi: 10.1152/jn.1997.77.6.3035.
Adenosine modulation of calcium channel currents and synaptic gamma-aminobutyrate (GABA) release was investigated with whole cell voltage-clamp recordings in rat suprachiasmatic nucleus (SCN) and arcuate nucleus cultures (n = 94). In SCN cultures, approximately 70% of the neurons showed a reversible inhibition of whole cell barium currents on the application of adenosine or its analogues. Adenosine at 1 microM reduced the amplitude of the barium currents by approximately 27%. In contrast to the significant reduction in the amplitude, the rising and decaying phases of the barium currents, and the inverted bell shape of the current-voltage curve of the barium currents, were not changed by adenosine. The adenosine A1 receptor agonist N6-cyclopentyladenosine (CPA; 100 nM) and the adenosine A2 receptor agonist N6-[2-(3,5-dimethoxyphenyl)-ethyl]adenosine (DPMA; 100 nM) inhibited the barium currents by 21% and 16%, respectively, in SCN neurons, indicating both A1 and A2 receptor actions. The A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (100 nM) significantly reduced the effect of CPA but did not change the effect of DPMA on the barium currents. In the presence of tetrodotoxin to block action potentials, the frequency, but not the amplitude, of miniature inhibitory postsynaptic currents was significantly reduced (46%) by 1 microM adenosine, suggesting a presynaptic mechanism of adenosine action. In support of this suggestion, the postsynaptic GABA receptor responses were not influenced by 1 microM adenosine in the majority of SCN neurons. Most solitary self-innervating SCN neurons in microisland cultures were GABAergic. In these cells, the evoked autaptic GABA release (inhibitory postsynaptic current) was significantly inhibited by adenosine (37%), CPA (27%), and DPMA (28%), indicating that both A1 and A2 receptors were present in presynaptic axons. Similar to the effect in SCN neurons, adenosine inhibited both barium currents and GABA release in arcuate neurons. The reduction of whole cell barium currents by adenosine (1 microM), CPA (100 nM), and DPMA (100 nM) was 24, 17, and 19%, respectively. In solitary self-innervating arcuate neurons, adenosine inhibited the evoked GABA release (inhibitory postsynaptic current) by approximately 48%. We conclude that both adenosine A1 and A2 receptors are present in the SCN and arcuate nucleus of the hypothalamus. Adenosine inhibits calcium currents and presynaptically reduces inhibitory GABA neurotransmission.
采用全细胞膜片钳记录技术，在大鼠视交叉上核（SCN）和弓状核培养物（n = 94）中研究了腺苷对钙通道电流及突触γ-氨基丁酸（GABA）释放的调节作用。在SCN培养物中，约70%的神经元在应用腺苷或其类似物后，全细胞钡电流出现可逆性抑制。1 μM腺苷使钡电流幅度降低约27%。与幅度显著降低形成对比的是，腺苷并未改变钡电流的上升和衰减相，以及钡电流-电压曲线的倒钟形。腺苷A1受体激动剂N6-环戊基腺苷（CPA；100 nM）和腺苷A2受体激动剂N6-[2-(3,5-二甲氧基苯基)-乙基]腺苷（DPMA；100 nM）分别使SCN神经元的钡电流抑制21%和16%，表明A1和A2受体均发挥作用。A1受体拮抗剂8-环戊基-1,3-二丙基黄嘌呤（100 nM）显著降低了CPA对钡电流的作用，但未改变DPMA的作用。在存在河豚毒素以阻断动作电位的情况下，1 μM腺苷使微小抑制性突触后电流的频率显著降低（46%），但幅度未变，提示腺苷作用于突触前机制。支持这一观点的是，在大多数SCN神经元中，1 μM腺苷并未影响突触后GABA受体反应。微岛培养中大多数孤立的自支配SCN神经元为GABA能神经元。在这些细胞中，诱发的自突触GABA释放（抑制性突触后电流）被腺苷（37%）、CPA（27%）和DPMA（28%）显著抑制，表明突触前轴突中同时存在A1和A2受体。与在SCN神经元中的作用类似，腺苷在弓状核神经元中同时抑制钡电流和GABA释放。腺苷（1 μM）、CPA（100 nM）和DPMA（100 nM）使全细胞钡电流分别降低24%、17%和19%。在孤立的自支配弓状核神经元中，腺苷使诱发的GABA释放（抑制性突触后电流）降低约48%。我们得出结论，下丘脑的SCN和弓状核中均存在腺苷A1和A2受体。腺苷抑制钙电流并在突触前减少抑制性GABA神经传递。
