Pan W J, Osmanović S S, Shefner S A
Department of Physiology and Biophysics, University of Illinois at Chicago, USA.
J Pharmacol Exp Ther. 1995 Apr;273(1):537-44.
The effect of adenosine on locus ceruleus neurons was investigated with intracellular recording in a totally submerged brain slice preparation. Bath application of adenosine (100 microM) hyperpolarized locus ceruleus neurons and inhibited their spontaneous firing; under voltage-clamp conditions, adenosine activated an inwardly rectifying, outward current (IAdo). The reversal potential of the IAdo was -110 mV and shifted by 59.2 mV per 10-fold change in external K+ concentration, very close to the shift predicted by the Nernst equation for a pure K+ current. The IAdo was due to a direct postsynaptic action, because it persisted in low Ca++/high Mg++ media that block Ca(++)-dependent neurotransmitter release. The IAdo was not blocked by glibenclamide, which indicates that it is not mediated by ATP-dependent K+ channels. The adenosine-activated current was concentration-dependent (10 microM-1 mM adenosine) and was blocked by the selective A1 antagonist 8-cyclopentyltheophylline in a competitive manner. Schild analysis in two neurons yielded estimates of the Kd value for 8-cyclopentyltheophylline of 1.4 and 4.6 nM, which indicates that the IAdo is mediated by A1 adenosine receptors. The adenosine-induced hyperpolarization, inhibition of firing and activation of outward current were blocked by external barium, but not by 4-aminopyridine. By contrast, we have previously shown that adenosine enhances A-current, thereby reducing action potential duration in locus ceruleus neurons, and these effects are blocked by 4-aminopyridine but not barium. These data indicate that the adenosine-induced hyperpolarization and inhibition of firing are mediated by the IAdo and that these effects are independent of adenosine's enhancement of A-current.
采用全浸没脑片制备技术，通过细胞内记录研究了腺苷对蓝斑神经元的作用。浴加腺苷（100微摩尔）可使蓝斑神经元超极化并抑制其自发放电；在电压钳条件下，腺苷激活内向整流外向电流（IAdo）。IAdo的反转电位为-110毫伏，外部钾离子浓度每变化10倍，其电位移动59.2毫伏，这与能斯特方程预测的纯钾离子电流的移动非常接近。IAdo是由直接的突触后作用引起的，因为它在阻断钙离子依赖性神经递质释放的低钙/高镁介质中持续存在。IAdo不受格列本脲阻断，这表明它不是由ATP依赖性钾通道介导的。腺苷激活的电流具有浓度依赖性（10微摩尔-1毫摩尔腺苷），并被选择性A1拮抗剂8-环戊基茶碱竞争性阻断。对两个神经元进行的希尔德分析得出8-环戊基茶碱的Kd值估计为1.4和4.6纳摩尔，这表明IAdo是由A1腺苷受体介导的。腺苷诱导的超极化、放电抑制和外向电流激活被外部钡阻断，但不被4-氨基吡啶阻断。相比之下，我们之前已经表明，腺苷增强A电流，从而缩短蓝斑神经元的动作电位时程，而这些作用被4-氨基吡啶阻断，但不被钡阻断。这些数据表明，腺苷诱导的超极化和放电抑制是由IAdo介导的，并且这些作用独立于腺苷对A电流的增强作用。
