Deri Z, Bors P, Adam-Vizi V
Department of Biochemistry II. Semmelweis University of Medicine, Budapest, Hungary.
J Neurochem. 1993 Mar;60(3):1065-72. doi: 10.1111/j.1471-4159.1993.tb03255.x.
We studied the effect of alpha-latrotoxin (alpha LTX) on [14C]acetylcholine ([14C]ACh) release, intracellular Ca2+ concentration ([Ca2+]i). plasma membrane potential, and high-affinity choline uptake of synaptosomes isolated from guinea pig cortex. alpha LTX (10(-10)-10(-8) M) caused an elevation of the [Ca2+]i as detected by Fura 2 fluorescence and evoked [14C]ACh efflux. Two components in the action of the toxin were distinguished: one that required the presence of Na+ in the external medium and another that did not Displacement of Na+ by sucrose or N-methylglucamine in the medium considerably decreased the elevation of [Ca2+]i and [14C]ACh release by alpha LTX. The Na(+)-dependent component of the alpha LTX action was obvious in the inhibition of the high-affinity choline uptake of synaptosomes. Some of the toxin action on both [Ca2+]i and [14C]ACh release remained in the absence of Na+. Both the Na(+)-dependent and the Na(+)-independent components of the alpha LTX-evoked [14C]ACh release partly required the presence of either Mg2+ or Ca2+. The nonneurotransmitter [14C]choline was released along with [14C]ACh, but this release did not depend on the presence of either Na+ or Ca2+, indicating nonspecific leakage through the plasma membrane. We conclude that there are two factors in the release of ACh from synaptosomes caused by the toxin: (1) cation-dependent ACh release, which is related to (a) Na(+)-dependent divalent cation entry and (b) Na(+)-independent divalent cation entry, and (2) non-specific Na(+)- and divalent cation-independent leakage.
我们研究了α-银环蛇毒素（α-LTX）对从豚鼠皮层分离的突触体中[14C]乙酰胆碱（[14C]ACh）释放、细胞内钙离子浓度（[Ca2+]i）、质膜电位和高亲和力胆碱摄取的影响。α-LTX（10^(-10)-10^(-8)M）通过Fura 2荧光检测引起[Ca2+]i升高，并诱发[14C]ACh外流。毒素作用可分为两个部分：一个部分需要外部介质中存在Na+，另一个部分则不需要。介质中用蔗糖或N-甲基葡糖胺取代Na+会显著降低α-LTX引起的[Ca2+]i升高和[14C]ACh释放。α-LTX作用的Na+依赖性部分在抑制突触体高亲和力胆碱摄取方面很明显。在没有Na+的情况下，毒素对[Ca2+]i和[14C]ACh释放仍有一些作用。α-LTX诱发的[14C]ACh释放的Na+依赖性和非Na+依赖性部分都部分需要Mg2+或Ca2+的存在。非神经递质[14C]胆碱与[14C]ACh一起释放，但这种释放不依赖于Na+或Ca2+的存在，表明是通过质膜的非特异性渗漏。我们得出结论，毒素引起突触体释放ACh有两个因素：（1）阳离子依赖性ACh释放，这与（a）Na+依赖性二价阳离子内流和（b）非Na+依赖性二价阳离子内流有关；（2）非特异性的不依赖Na+和二价阳离子的渗漏。
