A rapid exocytosis mode in chromaffin cells with a neuronal phenotype.

AbstractWe have used astrocyte-conditioned medium (ACM) to pro-mote the transdifferentiation of bovine chromaffin cells andstudy modifications in the exocytotic process when these cellsacquire a neuronal phenotype. In the ACM-promoted neuronalphenotype, secretory vesicles and intracellular Ca 2+ rise werepreferentially distributed in the neurite terminals. Using am-perometry, we observed that the exocytotic events also oc-curred mainly in the neurite terminals, wherein the individualexocytotic events had smaller quantal size than in undiffer-entiated cells. Additionally, duration of pre-spike current wassignificantly shorter, suggesting that ACM also modifies thefusion pore stability. After long exposure (7–9 days) to ACM,the kinetics of catecholamine release from individual vesicleswas markedly accelerated. The morphometric analysis ofvesicle diameters suggests that the rapid exocytotic eventsobserved in neurites of ACM-treated cells correspond to theexocytosis of large dense-core vesicles (LDCV). On the otherhand, experiments performed in EGTA-loaded cells suggestthat ACM treatment promotes a better coupling betweenvoltage-gated calcium channels (VGCC) and LDCV. Thus, ourfindings reveal that ACM promotes a neuronal phenotype inchromaffin cells, wherein the exocytotic kinetics is acceler-ated. Such rapid exocytosis mode could be caused at least inpart by a better coupling between secretory vesicles andVGCC.Keywords: astrocytes, catecholamines, chromaffin cells,exocytosis, neurotrophic factors, large dense-core vesicles.J. Neurochem. (2006) 99, 29–41.