cAmp modulates exocytotic kinetics and increases quantal size in chromaffin cells.
The role of cAMP/cAMP-dependent protein kinase (PKA) on the late phase of exocytosis has been studied by amperometry on Ba(2+)-stimulated single bovine chromaffin cells. Forskolin (FSK) increases the intracellular cAMP levels in a concentration-dependent manner. Forskolin (100 nM) does not increase the number of exocytotic events, although it significantly increases the net granule content of catecholamines (CA), which is accompanied by a slowing of the process of degranulation. These effects are reversible, occur within 15 to 60 s, and are not due to newly synthesized CA. Isoprenaline, pituitary adenylate cyclase-activating polypeptide-38 or dB-cAMP reproduce FSK effects as does cholera toxin. The inhibition of phosphodiesterases with 3-isobutyl-1-methylxanthine mimics and potentiates the effect of FSK and isoprenaline. Rolipram and okadaic acid also produce a drastic increase in net granule content of CA, whereas H-89 attenuates the FSK response. These data indicate that cyclic AMP/PKA might favor the granule aggregation before its fusion with cell membrane and slow the late step of the exocytotic process.
Machado
J D
JD
Unidad de Farmacología, Facultad de Medicina, Universidad de La Laguna, Tenerife, Spain.
Morales
A
A
Gomez
J F
JF
Borges
R
R
D000818:Animals; D002417:Cattle; D002478:Cells, Cultured; D019439:Chromaffin Cells / Q000187:drug effects* / Q000502:physiology; D002837:Chromaffin Granules / Q000187:drug effects / Q000502:physiology; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000737:chemistry / Q000494:pharmacology*; D005089:Exocytosis / Q000187:drug effects*; D007545:Isoproterenol / Q000494:pharmacology; D007700:Kinetics; D018716:Molecular Mimicry; D009479:Neuropeptides / Q000494:pharmacology; D009569:Nitric Oxide / Q000378:metabolism; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide; D013569:Synapses / Q000187:drug effects; D014665:Vasodilator Agents / Q000494:pharmacology
D009479:Neuropeptides; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide; D014665:Vasodilator Agents; D005576:Colforsin; D009569:Nitric Oxide; D000242:Cyclic AMP; D007545:Isoproterenol