title: Mouse chromaffin cells have two populations of dense core vesicles.
abstract: The quantal hypothesis states that neurotransmitter is released in discrete packages, quanta, thought to represent the neurotransmitter content of individual vesicles. If true, then vesicle size should influence quantal size. Although chromaffin cells are generally thought to have a single population of secretory vesicles, our electron microscopy analysis suggested two populations as the size distribution was best described as the sum of two Gaussians. The average volume difference was fivefold. To test whether this difference in volume affected quantal size, neurotransmitter release from permeabilized cells exposed to 100 microM Ca2+ was measured with amperometry. Quantal content was bimodally distributed with both large and small events; the distribution of vesicle sizes predicted by amperometry was extremely similar to those measured with electron microscopy. In addition, each population of events exhibited distinct release kinetics. These results suggest that chromaffin cells have two populations of dense core vesicles (DCV) with unique secretory properties and which may represent two distinct synthetic pathways for DCV biogenesis or alternatively they may represent different stages of biosynthesis.
authors.affiliation: Department of Neurobiology, Pharmacology, and Physiology, The University of Chicago, 947 E. 58 St., Chicago, Illinois 60637, USA. cpg22@email.med.yale.edu
authors.forename: Chad P
authors.initials: CP
authors.lastname: Grabner
authors.forename: Steven D
authors.initials: SD
authors.lastname: Price
authors.forename: Anna
authors.initials: A
authors.lastname: Lysakowski
authors.forename: Aaron P
authors.initials: AP
authors.lastname: Fox
mesh_terms: D000313:Adrenal Medulla / Q000166:cytology*; D000818:Animals; D000831:Animals, Newborn; D048429:Cell Size; D002478:Cells, Cultured; D019439:Chromaffin Cells / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure*; D002837:Chromaffin Granules / Q000648:ultrastructure; D004072:Digitonin / Q000494:pharmacology; D004558:Electric Stimulation; D007202:Indicators and Reagents / Q000494:pharmacology; D007425:Intracellular Membranes / Q000187:drug effects / Q000648:ultrastructure; D051379:Mice; D008810:Mice, Inbred C57BL; D046529:Microscopy, Electron, Transmission / Q000379:methods; D009538:Nicotine / Q000494:pharmacology; D018722:Nicotinic Agonists; D022142:Secretory Vesicles / Q000145:classification / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure*
chemical_list: D007202:Indicators and Reagents; D018722:Nicotinic Agonists; D009538:Nicotine; D004072:Digitonin