Exocytotic catecholamine release is not associated with cation flux through channels in the vesicle membrane but Na+ influx through the fusion pore.
Release of charged neurotransmitter molecules through a narrow fusion pore requires charge compensation by other ions. It has been proposed that this may occur by ion flow from the cytosol through channels in the vesicle membrane, which would generate a net outward current. This hypothesis was tested in chromaffin cells using cell-attached patch amperometry that simultaneously measured catecholamine release from single vesicles and ionic current across the patch membrane. No detectable current was associated with catecholamine release indicating that <2% of cations, if any, enter the vesicle through its membrane. Instead, we show that flux of catecholamines through the fusion pore, measured as an amperometric foot signal, decreases when the extracellular cation concentration is reduced. The results reveal that the rate of transmitter release through the fusion pore is coupled to net Na+ influx through the fusion pore, as predicted by electrodiffusion theory applied to fusion-pore permeation, and suggest a prefusion rather than postfusion role for vesicular cation channels.
Gong
Liang-Wei
LW
School of Applied and Engineering Physics, Cornell University, 217 Clark Hall, Ithaca, NY 14850, USA.
de Toledo
Guillermo Alvarez
GA
Lindau
Manfred
M
D000818:Animals; D001692:Biological Transport / Q000502:physiology; D002395:Catecholamines / Q000378:metabolism*; D002412:Cations / Q000378:metabolism*; D002417:Cattle; D002462:Cell Membrane / Q000378:metabolism; D002463:Cell Membrane Permeability; D002478:Cells, Cultured; D019439:Chromaffin Cells / Q000166:cytology / Q000378:metabolism; D025802:Electric Capacitance; D005089:Exocytosis / Q000502:physiology*; D007473:Ion Channels / Q000378:metabolism*; D008561:Membrane Fusion / Q000502:physiology*; D018408:Patch-Clamp Techniques; D022142:Secretory Vesicles / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*
D002395:Catecholamines; D002412:Cations; D007473:Ion Channels; D012964:Sodium