Effect of alpha-latrotoxin on acetylcholine release and intracellular Ca2+ concentration in synaptosomes: Na(+)-dependent and Na(+)-independent components.
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.
Deri
Z
Z
Department of Biochemistry II. Semmelweis University of Medicine, Budapest, Hungary.
Bors
P
P
Adam-Vizi
V
V
D000109:Acetylcholine / Q000378:metabolism*; D000818:Animals; D001667:Binding, Competitive; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002794:Choline / Q000378:metabolism; D003470:Culture Media; D006168:Guinea Pigs; D007425:Intracellular Membranes / Q000378:metabolism*; D008274:Magnesium / Q000494:pharmacology; D009994:Osmolar Concentration; D012964:Sodium / Q000494:pharmacology*; D013111:Spider Venoms / Q000494:pharmacology*; D013574:Synaptosomes / Q000378:metabolism*
D003470:Culture Media; D013111:Spider Venoms; C020763:alpha-latrotoxin; D012964:Sodium; D008274:Magnesium; D002794:Choline; D000109:Acetylcholine; D002118:Calcium