Ashley R H
Biochim Biophys Acta. 1986 Jan 29;854(2):207-12. doi: 10.1016/0005-2736(86)90112-4.
In a physiological medium the resting membrane potential of synaptosomes from guinea-pig cerebral cortex, estimated from rhodamine 6G fluorescence measurements, was nearly -50mV. This agreed with calculations using the Goldman-Hodgkin-Katz equation. With external [Ca2+] less than or equal to 3 mM veratridine depolarisation (to -30 mV) was accompanied by increases in intrasynaptosomal free calcium concentrations (monitored by entrapped quin2) and parallel increases in total acetylcholine release. With external [Ca2+] greater than 3 mM both intrasynaptosomal free calcium concentrations and transmitter release were paradoxically reduced, providing further evidence for a close correlation between the two events. To support an explanation of these findings based on divalent cation screening of membrane surface charge (increasing the voltage gradient within the membrane and closing voltage-inactivated channels) surface potential measurements were made on synaptic lipid liposomes by using a fluorescent surface-bound pH indicator. These experiments provided evidence for the presence of screenable surface charge on synaptosomes, and it was further shown in depolarised synaptosomes themselves that total external [Ca2+ + Mg2+], and not [Ca2+] alone, set the observed peak in intrasynaptosomal free calcium.
在生理介质中，通过罗丹明6G荧光测量估算，豚鼠大脑皮层突触体的静息膜电位接近-50mV。这与使用戈德曼-霍奇金- Katz方程的计算结果一致。当细胞外[Ca2+]小于或等于3 mM时，藜芦碱去极化（至-30 mV）伴随着突触体内游离钙浓度的增加（通过包埋的喹啉2监测）以及总乙酰胆碱释放的平行增加。当细胞外[Ca2+]大于3 mM时，突触体内游离钙浓度和递质释放都反常地降低，这为这两个事件之间的密切相关性提供了进一步的证据。为了支持基于二价阳离子对膜表面电荷的筛选（增加膜内电压梯度并关闭电压失活通道）对这些发现的解释，通过使用荧光表面结合pH指示剂对突触脂质脂质体进行了表面电位测量。这些实验为突触体上存在可筛选的表面电荷提供了证据，并且进一步表明，在去极化的突触体本身中，是细胞外[Ca2+ + Mg2+]的总和，而不仅仅是[Ca2+]，设定了观察到的突触体内游离钙的峰值。
