Quantal size is dependent on stimulation frequency and calcium entry in calf chromaffin cells.
To what extent the quantal hypothesis of transmitter release applies to dense-core vesicle (DCV) secretion is unknown. We determined the characteristics of individual secretory events in calf chromaffin cells using catecholamine amperometry combined with different patterns of stimulation. Raising the frequency of action potential trains from 0.25-10 Hz in 2 mM [Ca(2+)]o or [Ca(2+)]o from 0.25-7 mM at 7 Hz elevated the amount released per event (quantal size). With increased stimulation, quantal size rose continuously, not abruptly, suggesting that release efficiency from a single population of DCVs rather than recruitment of different-sized vesicles contributed to the effect. These results suggest that catecholamine secretion does not conform to the quantal model. Inhibition of rapid endocytosis damped secretion in successive episodes, implying an essential role for this process in the recycling of vesicles needed for continuous secretion.
Elhamdani
A
A
Department of Pharmacology, Wayne State University School of Medicine, Detroit, MI 48201, USA.
Palfrey
H C
HC
Artalejo
C R
CR
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology*; D000313:Adrenal Medulla / Q000187:drug effects / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D002395:Catecholamines / Q000378:metabolism; D002417:Cattle; D019439:Chromaffin Cells / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D004558:Electric Stimulation; D004705:Endocytosis / Q000187:drug effects / Q000502:physiology; D009431:Neural Conduction / Q000187:drug effects / Q000502:physiology; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D022142:Secretory Vesicles / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D013569:Synapses / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology*
D002395:Catecholamines; D002118:Calcium