Catecholamine release from PC12 cells

In comparison, Finnegan et al. have also utilized amperometric detection to examine exocytotic release from PC12 cells [12]. A histogram, also presented in Figure 5, exhibits a relative SD of 15%. In agreement with the results from the other cell types, this SD is similar to the previously reported relative SD of PC12 vesicular radii (25%) [29]. A mean vesicular radius of 79 nm [29] has been used to determine a mean PC 12 vesicular catecholamine concentration of 99 mM. 

Exocytosis from differentiated cells occurs preferentially at the varicosities with very little release, if any, from the smooth processes or cell body [3], The absence of exocytotic events at the cell body of the differentiated cells could be the result of changes in surface morphology and in the expression and distribution of ion channels in PC12 cells upon differentiation [3], The absence of catecholamine release from the smooth processes is most likely due to the fact that vesicles do not appear in these locations. The average vesicular catecholamine content observed for exocytosis at varicosities is 178 9 zmol (107,000 molecules), which is not significantly different from that observed at undifferentiated cells however, a more narrow distribution is observed for the NGF-treated cells (Figure 19). 

Chen, T.K., G.A. Luo, and A.G. Ewing. 1994. Amperometric monitoring of stimulated catecholamine release from rat pheochromocytoma (PC12) cells at the zeptomole level. Anal. Ghent. 66 3031-3035. 

Secretion by chromaffin cells has been our specific area of interest. To study the final events during secretion by exocytosis, bovine adrenal chromaffin cells in shortterm culture and rat pheochromocytoma (PC12) cells are used. Both cell types take up labeled catecholamines and store them within secretory vesicles from which they can be released on stimulation. The released catecholamines can be detected in the supernatant. After permeabilization of the plasma membrane, release of catecholamines can be triggered by micromolar concentrations of free Ca (Ahnert-Hilger etaL, 1985, 1989b, 1992). 

Figure 19 Distribution of vesicle content for potassium-stimulated release at varicosities plotted as the cubed root of catecholamine released. Plots of the percent of total events observed in the first 40 s following initiation of release vs. the cubed root of the amount of catecholamine released upon elevated potassium stimulation for (A) 17 undifferentiated PC12 cells (475 total release events) and (B) 16 differentiated PC 12 cells (156 total release events). (Reproduced from Brain Res. with permission [3].)...

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