title: Influence of quantal size and cAMP on the kinetics of quantal catecholamine release from rat chromaffin cells.
abstract: Using carbon fiber amperometry, we exploited the natural variation in quantal size (Q) among individual granules in rat chromaffin cells to examine the influence of Q on quantal release kinetics. Although it is generally accepted that granules with larger Q have slower kinetics of release, we found that this trend was applicable only to granules with Q(1/3) < 0.6 pC(1/3). Granules with larger Q adapted specific mechanisms to maintain a rapid kinetic of release. The semistable fusion pores in the large-Q granules persisted for a longer duration and could reach a bigger size before the onset of very rapid dilation to allow a longer and larger foot signal. Most importantly, a large proportion of large-Q granules maintained a relatively short half-width in the main spike. This suggests that the most rapid phase of fusion pore dilation in many large-Q granules may be faster than that in small-Q granules. Moreover, cAMP selectively advanced the onset of the rapid dilation of the fusion pore in the large- but not the small-Q granules. Thus, our finding raises the possibility that fusion pore and/or granule matrix in small- and large-Q granules may have different molecular structures.
authors.affiliation: Department of Pharmacology and Centre for Neuroscience, University of Alberta, Edmonton, Alberta, Canada.
authors.forename: Kim San
authors.initials: KS
authors.lastname: Tang
authors.forename: Nan
authors.initials: N
authors.lastname: Wang
authors.forename: Amy
authors.initials: A
authors.lastname: Tse
authors.forename: Frederick W
authors.initials: FW
authors.lastname: Tse
mesh_terms: D000818:Animals; D002395:Catecholamines / Q000378:metabolism*; D002478:Cells, Cultured; D019439:Chromaffin Cells / Q000378:metabolism*; D002837:Chromaffin Granules / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism*; D005089:Exocytosis / Q000502:physiology*; D007700:Kinetics; D008297:Male; D008657:Metabolic Clearance Rate; D010316:Particle Size; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D002395:Catecholamines; D000242:Cyclic AMP