Nitric oxide modulates a late step of exocytosis.
The effects of nitric oxide (NO) on the late phase of exocytosis have been studied, by amperometry, on Ba(2+)-stimulated chromaffin cells. Acute incubation with NO or NO donors (sodium nitroprusside, spermine-NO, S-nitrosoglutathione) produced a drastic slowdown of the granule emptying. Conversely, cell treatment with N(omega)-nitro-l-arginine methyl ester (a NO synthase inhibitor) or with NO scavengers (methylene blue, 2-(4-carboxyphenyl)-4,4,5, 5-tetramethyl-imidazoline-1-oxyl-3-oxide potassium) accelerated the extrusion of catecholamines from chromaffin granules, suggesting the presence of a NO modulatory tone. The incubation with phosphodiesterase inhibitors (3-isobutyl-1-methylxanthine or zaprinast) or with the cell-permeant cGMP analog 8-bromo-cGMP, mimicked the effects of NO, suggesting the involvement of the guanylate cyclase cascade. NO effects were not related to changes in intracellular Ba(2+). NO did not modify the duration of feet. Effects were evident even on pre-fusioned granules, observed under hypertonic conditions, suggesting that the fusion pore is not the target for NO, which probably acts by modifying the affinity of catecholamines for the intragranular matrix. NO could modify the synaptic transmitter efficacy through a novel mechanism, which involves the regulation of the emptying of secretory vesicles.
Machado
J D
JD
Unidad de Farmacologia, Facultad de Medicina, Universidad de La Laguna, 38071 La Laguna, Tenerife, Spain.
Segura
F
F
Brioso
M A
MA
Borges
R
R
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000818:Animals; D001464:Barium / Q000494:pharmacology; D002395:Catecholamines / Q000378:metabolism; D002417:Cattle; D019439:Chromaffin Cells / Q000187:drug effects; D002837:Chromaffin Granules / Q000187:drug effects* / Q000378:metabolism; D006152:Cyclic GMP / Q000031:analogs & derivatives / Q000494:pharmacology; D004563:Electrochemistry; D005089:Exocytosis / Q000187:drug effects*; D007700:Kinetics; D019331:NG-Nitroarginine Methyl Ester / Q000494:pharmacology; D009569:Nitric Oxide / Q000494:pharmacology*; D009599:Nitroprusside; D009603:Nitroso Compounds / Q000494:pharmacology
D002395:Catecholamines; D009603:Nitroso Compounds; D009599:Nitroprusside; D001464:Barium; C016276:8-bromocyclic GMP; D009569:Nitric Oxide; D006152:Cyclic GMP; D015056:1-Methyl-3-isobutylxanthine; D019331:NG-Nitroarginine Methyl Ester