Calcium-dependent transmitter secretion from fibroblasts: modulation by synaptotagmin I.
Following endocytic uptake of acetylcholine (ACh), CHO fibroblasts exhibit Ca(2+)-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 I, an integral membrane protein of synaptic vesicles, showed a reduced spontaneous quantal ACh release and an enhanced Ca(2+)-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 Ca2+. Through inhibition of exocytosis at the resting intracellular concentration of Ca2+ and removal of the inhibition upon depolarization-induced Ca2+ entry, synaptotagmin I could enhance the efficiency of excitation-secretion coupling.
Morimoto
T
T
Department of Biological Sciences, Columbia University, New York, New York 10027, USA.
Popov
S
S
Buckley
K M
KM
Poo
M M
MM
D000109:Acetylcholine / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D016466:CHO Cells; D002118:Calcium / Q000494:pharmacology*; D002135:Calcium-Binding Proteins; D002478:Cells, Cultured; D006224:Cricetinae; D004705:Endocytosis / Q000187:drug effects; D005089:Exocytosis; D005347:Fibroblasts / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D006735:Horseradish Peroxidase / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000235:genetics / Q000494:pharmacology*; D008854:Microscopy, Electron; D009132:Muscles / Q000502:physiology; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000494:pharmacology*; D050863:Synaptotagmin I; D050857:Synaptotagmins; D014162:Transfection; D014981:Xenopus
D002135:Calcium-Binding Proteins; D008562:Membrane Glycoproteins; D009419:Nerve Tissue Proteins; D050863:Synaptotagmin I; D050857:Synaptotagmins; D000255:Adenosine Triphosphate; D006735:Horseradish Peroxidase; D000109:Acetylcholine; D002118:Calcium