Brain Keith L, Jackson V Margaret, Trout Stephen J, Cunnane Thomas C
University Department of Pharmacology, University of Oxford, Mansfield Road, UK.
J Physiol. 2002 Jun 15;541(Pt 3):849-62. doi: 10.1113/jphysiol.2002.019612.
A confocal Ca2+ imaging technique has been used to detect ATP release from individual sympathetic varicosities on the same nerve terminal branch. Varicose nerve terminals and smooth muscle cells in mouse vas deferens were loaded with the Ca2+ indicator Oregon Green 488 BAPTA-1. Field (nerve) stimulation evoked discrete, focal increases in [Ca2+] in smooth muscle cells adjacent to identified varicosities. These focal increases in [Ca2+] have been termed 'neuroeffector Ca2+ transients' (NCTs). NCTs were abolished by alpha,beta-methylene ATP (1 microM), but not by nifedipine (1 microM) or prazosin (100 nM), suggesting that NCTs are generated by Ca2+ influx through P2X receptors without a detectable contribution from L-type Ca2+ channels or alpha(1)-adrenoceptor-mediated pathways. Action potential-evoked ATP release was highly intermittent (mean probability 0.019 +/- 0.002; range 0.001-0.10) at 1 Hz stimulation, even though there was no failure of action potential propagation in the nerve terminals. Twenty-eight per cent of varicosities failed to release transmitter following more than 500 stimuli. Spontaneous ATP release was very infrequent (0.0014 Hz). No Ca2+ transient attributable to noradrenaline release was detected even in response to 5 Hz stimulation. There was evidence of local noradrenaline release as the alpha(2)-adrenoceptor antagonist yohimbine increased the probability of occurrence of NCTs by 55 +/- 21 % during trains of stimuli at 1 Hz. Frequency-dependent facilitation preferentially occurred at low probability release sites. The monitoring of NCTs now allows transmitter release to be detected simultaneously from each functional varicosity on an identified nerve terminal branch on an impulse-to-impulse basis.
一种共聚焦钙成像技术已被用于检测同一神经末梢分支上单个交感神经膨体的ATP释放。小鼠输精管中的曲张神经末梢和平滑肌细胞被加载了钙指示剂俄勒冈绿488 BAPTA-1。场（神经）刺激引起已识别膨体附近平滑肌细胞中[Ca2+]的离散、局部增加。这些[Ca2+]的局部增加被称为“神经效应器钙瞬变”（NCTs）。NCTs被α,β-亚甲基ATP（1μM）消除，但不被硝苯地平（1μM）或哌唑嗪（100 nM）消除，这表明NCTs是由通过P2X受体的钙内流产生的，而L型钙通道或α(1)-肾上腺素能受体介导的途径没有可检测到的贡献。在1 Hz刺激下，动作电位诱发的ATP释放高度间歇性（平均概率0.019±0.002；范围0.001-0.10），尽管神经末梢中动作电位的传播没有失败。超过500次刺激后，28%的膨体未能释放递质。自发ATP释放非常罕见（0.0014 Hz）。即使在5 Hz刺激下，也未检测到归因于去甲肾上腺素释放的钙瞬变。有证据表明存在局部去甲肾上腺素释放，因为α(2)-肾上腺素能受体拮抗剂育亨宾在1 Hz的刺激串期间将NCTs发生的概率提高了55±21%。频率依赖性易化优先发生在低概率释放部位。现在，对NCTs的监测允许在逐个脉冲的基础上同时检测来自已识别神经末梢分支上每个功能膨体的递质释放。
