Mechanisms underlying phasic and sustained secretion in chromaffin cells from mouse adrenal slices.
Many neurosecretory preparations display two components of depolarization-induced exocytosis: a phasic component synchronized with Ca2+ channel opening, followed by a slower sustained component. We evaluated possible mechanisms underlying this biphasic behavior by stimulating mouse chromaffin cells in situ with both depolarizations and flash photolysis of caged Ca2+. From a direct comparison of the secretory responses to both stimuli, we conclude that phasic and sustained release components originate from a readily releasable pool (RRP) of equally fusion-competent vesicles, suggesting that differences in the vesicles' proximity to Ca2+ channels underlie the biphasic secretory behavior. An intermediate pool in dynamic equilibrium with the RRP ensures rapid recruitment of release-ready vesicles after RRP depletion. Our results are discussed in terms of a refined model for secretion in chromaffin cells.
Voets
T
T
Department of Membrane Biophysics, Max-Planck-Institute for Biophysical Chemistry, Göttingen, Federal Republic of Germany. tvoets@gwdg.de
Neher
E
E
Moser
T
T
D000311:Adrenal Glands / Q000166:cytology* / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000493:pharmacokinetics; D015220:Calcium Channels / Q000502:physiology*; D019439:Chromaffin Cells / Q000737:chemistry* / Q000378:metabolism*; D003594:Cytoplasmic Granules / Q000737:chemistry / Q000378:metabolism*; D004553:Electric Conductivity; D004594:Electrophysiology; D005089:Exocytosis / Q000502:physiology; D007700:Kinetics; D008561:Membrane Fusion / Q000502:physiology; D008564:Membrane Potentials / Q000502:physiology; D051379:Mice; D008815:Mice, Inbred Strains; D009924:Organ Culture Techniques; D010777:Photochemistry
D015220:Calcium Channels; D002118:Calcium