Single-cell measurements of quantal secretion induced by alpha-latrotoxin from rat adrenal chromaffin cells: dependence on extracellular Ca2+.
alpha-Latrotoxin (alpha-LT), from black widow spider venom, is a potent enhancer of the spontaneous quantal release of neurotransmitter from a variety of nerve terminals and clonal neurosecretory cells. Using electrochemical amperometry and estimation of membrane impedance by phase detection, we present evidence that alpha-LT induces exocytosis of catecholamines from rat adrenal chromaffin cells beginning as rapidly as 30 s after close application of the toxin. This release is largely dependent on adequate levels of extracellular Ca2+ ([Ca2+]o). Lowering [Ca2+]o from 2 mM to </= 10-20 microM reduces the alpha-LT-induced rise in membrane capacitance by at least sixfold, on average, and nearly abolishes alpha-LT-induced quantal amperometric events, while still permitting insertion of non-selective cation channels. Based on these experiments, we argue that the rapid onset of alpha-LT action in promoting massive quantal release from chromaffin cells is primarily due to an increase in the Ca2+ permeability of the plasma membrane through non-selective cation channels.
Barnett
D W
DW
Department of Medicine, Box 8217, Washington University School of Medicine, St. Louis, MO-63110, USA.
Liu
J
J
Misler
S
S
D000313:Adrenal Medulla / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology*; D002395:Catecholamines / Q000378:metabolism*; D002462:Cell Membrane / Q000502:physiology; D002463:Cell Membrane Permeability; D002838:Chromaffin System / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D004553:Electric Conductivity; D004563:Electrochemistry; D005089:Exocytosis; D007473:Ion Channels / Q000378:metabolism; D051381:Rats; D013111:Spider Venoms / Q000494:pharmacology*
D002395:Catecholamines; D007473:Ion Channels; D013111:Spider Venoms; C020763:alpha-latrotoxin; D002118:Calcium