Akerman K E, Nicholls D G
Eur J Biochem. 1981 Mar 16;115(1):67-73.
Ionophore A23187, a Ca2+/2H+ exchanger, has multiple effects on the function of isolated nerve endings (synaptosomes). (a) There is a net uptake of Ca2+, the rate of which increases with ionophore concentration. (b) When Ca2+ uptake is terminated by EGTA, the ionophore induces an apparent efflux of Ca2+. (c) The plasma-membrane potential, calculated from the 86Rb+ distribution, decreases slowly upon addition of the ionophore. (d) Release of [3H]noradrenaline induced by the ionophore consists of a rapid phase followed by a subsequent slower phase, which coincides with the fall in plasma-membrane potential. (e) Ouabain depolarizes the plasma membrane without inducing the rapid phase of transmitter release. (f) The membrane potential of intrasynaptosomal mitochondria determined in situ falls rapidly upon addition of A23187, and there is a synchronous increase in synaptosomal respiration. (g) All these effects require external Ca2+ and the same range of ionophore concentrations. (h) Using the respiratory stimulation induced by the ionophore in isolated mitochondria to calibrate the cytosolic concentration of free Ca2+ in intact synaptosomes it is concluded that the cytosolic Ca2+ required for release of [3H]noradrenaline is in the range 1-10 microM.
离子载体A23187是一种Ca2+/2H+交换剂，对分离的神经末梢（突触体）功能有多种影响。(a) 存在Ca2+的净摄取，其速率随离子载体浓度增加而增加。(b) 当用乙二醇双四乙酸（EGTA）终止Ca2+摄取时，离子载体诱导明显的Ca2+外流。(c) 根据86Rb+分布计算的质膜电位，在加入离子载体后缓慢下降。(d) 离子载体诱导的[3H]去甲肾上腺素释放包括一个快速相，随后是一个较慢的相，这与质膜电位的下降一致。(e) 哇巴因使质膜去极化，但不诱导递质释放的快速相。(f) 加入A23187后，原位测定的突触体内线粒体膜电位迅速下降，同时突触体呼吸同步增加。(g) 所有这些效应都需要细胞外Ca2+和相同范围的离子载体浓度。(h) 利用离子载体在分离的线粒体中诱导的呼吸刺激来校准完整突触体中游离Ca2+的胞质浓度，得出释放[3H]去甲肾上腺素所需的胞质Ca2+在1-10微摩尔范围内。
