Effect of Compounds Which Disrupt Proton Gradients on Secretion of Neurosecretory Proteins from PC12 Pheochromocytoma Cells

Treatment of PC12 cells with chroquine (10-50 microM) obliterated the low intragranular pH, as detected by Acridine Orange fluorescence, and depleted the cells of dopamine and norepinephrine. However, these concentrations of chloroquine did not prevent the release of the newly synthesized proteins which normally undergo stimulus-coupled secretion with the catecholamines. Higher concentrations of chloroquine (200 microM) and ammonium chloride (10 and 25 mM) inhibited the release of most of these proteins. This inhibition did not result from alterations in protein synthesis, since the profile of proteins synthesized was not substantially altered. Nor did the inhibition result from degradation of the neurosecretory proteins, since prelabeled proteins were capable of undergoing stimulated secretion from chloroquine-treated cells, as from normal cells. The findings indicated that the inhibition was at the step of packaging of the proteins into the neurosecretory granules. While release of the major secretory proteins, including chromogranin B, was inhibited with 200 microM chloroquine, chromogranin A was secreted upon stimulation of these cells. The results of this study indicate that an acidic intragranular pH is not a requirement for the packaging and secretion of neurosecretory proteins. Higher concentrations of chloroquine had a differential effect on the regulated secretion of different neurosecretory proteins.