Depolarization-induced changes of free intracellular Ca(2+) concentration and of [(3)H]dopamine release in...

The rat pheochromocytoma cell line PC12 undergoes morphological differentiation into neurone-like cells when exposed to nerve growth factor (NGF). We found that in PC12 cells the enzymatic activity of choline-acetyltransferase and of tyrosine hydroxylase changed very little during NGF exposure, while tyrosine hydroxylase activity increased during other treatments of the cells. These enzymes are rate limiting for the synthesis of cholinergic and adrenergic neurotransmitters, respectively. In order to learn more about mechanisms involved in catecholamine release from differentiating PC12 cells, we studied the effects of dihydropyridines and of ?-conotoxin on K(+)-depolarization-induced [Ca(2+)](i) transients measured with fura-2 and on [(3)H]dopamine release. These drugs act on different types of voltage-gated Ca channels. We found that in differentiated cells [Ca(2+)](i) transients in growth cones are more sensitive to ?-conotoxin than to dihydropyridines, while the opposite is true for cell bodies in both differentiated and undifferentiated cells. Concomitantly we saw a shift from dihydropyridine-sensitive [(3)H]dopamine release in undifferentiated cells to ?-conotoxin-sensitive release in differentiated cells. We conclude that different types of Ca channels are predominantly involved in [(3)H]dopamine release in undifferentiated and differentiated PC12 cells, respectively.