Neuron
Volume 15, Issue 3, September 1995, Pages 689-696
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Calcium-dependent transmitter secretion from fibroblasts: Modulation by synaptotagmin I

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Abstract

Following endocytic uptake of acetylcholine (ACh), CHO fibroblasts exhibit Ca2+-dependent spontaneous quantal ACh release and depolarization-evoked ACh release, as detected by a whole-cell voltage-clamped myocyte in contact with the fibroblast. CHO fibroblasts transfected with synaptotagmin 1, an integral membrane protein of synaptic vesicles, showed a reduced spontaneous quantal ACh release and an enhanced Ca2+-evoked ACh release, as compared with control cells. Biochemical and ultrastructural studies of endocytic activity using horseradish peroxidase as a marker further confirmed the inhibitory action of synaptotagmin I on spontaneous vesicular exocytosis and on elevated exocytosis induced by Caz+. Through inhibition of exocytosis at the resting intracellular concentration of Ca2+ and removal of the inhibition upon depolarization-induced Ca2+ entry, synaptotagmin 1 could enhance the efficiency of excitation-secretion coupling.

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Present address: Department of Physiology and Biophysics, University of Illinois at Chicago, Chicago, Illinois 60612.