valinomycin and Pheochromocytoma

Incubation with a K+/H+ ionophore nigericin attenuated the nerve growth factor (NGF)-induced neurite outgrowth in rat pheochromocytoma PC12 cells. However, a Na+/H+ ionophore monensin and a Ca2+ ionophore A23187 did not inhibited the neurite outgrowth. Nigericin also inhibited the NGF-caused induction of acetylcholinesterase and suppression of cell proliferation. These changes were dependent on the amount of the ionophore added to the culture. In addition, a distinct K+ ionophore, valinomycin, similarly inhibited the NGF-induced neuronal differentiation. These results suggest the presence of the K+ ionophore-sensitive mechanism in the NGF-induced differentiation system in PC12 cells.

Topics: Acetylcholinesterase; Adrenal Gland Neoplasms; Animals; Calcimycin; Cell Differentiation; Dose-Response Relationship, Drug; Kinetics; Monensin; Nerve Growth Factors; Neurites; Neurons; Nigericin; PC12 Cells; Pheochromocytoma; Potassium; Rats; Valinomycin

The dependence on Na+, K+, and Cl- of uptake and accumulation of [3H]noradrenaline was studied in plasma membrane vesicles isolated from PC-12 pheochromocytoma cells. Plasma membrane vesicles accumulated [3H]noradrenaline when an inward-directed gradient for Na+ and an outward-directed gradient for K+ were imposed across the vesicle membrane. Under these conditions, initial rates of uptake of [3H]noradrenaline were saturable (Km = 0.14 microM) and inhibited by a series of substrates and inhibitors of "uptake". The IC50 values were positively correlated with those for inhibition of uptake into intact PC-12 cells. Uptake and accumulation of [3H]noradrenaline in plasma membrane vesicles were absolutely dependent on external Na+ and Cl-; they were dependent on an inwardly directed gradient for Na+ but less dependent on an inwardly directed gradient for Cl-. Internal K+ strongly enhanced uptake and accumulation of [3H]noradrenaline. Rb+, but not Li+, had the capacity to replace internal K+. Two explanations are proposed for this effect of internal K+: (a) creation of a K+ diffusion potential (inside negative) provides a driving force for inward transport, and/or (b) K+ increases the turnover rate by formation of a highly mobile potassium-carrier complex. A hypothetical scheme for the transport of noradrenaline is presented.

Topics: Adrenal Gland Neoplasms; Animals; Biological Transport, Active; Carbonyl Cyanide m-Chlorophenyl Hydrazone; Cell Line; Cell Membrane; Chlorides; Ions; Kinetics; Lithium; Membrane Potentials; Neurons; Norepinephrine; Pheochromocytoma; Potassium; Rats; Rubidium; Sodium; Valinomycin

PC12, a clonal line of rat pheochromocytoma, accumulates newly synthesized acetylcholine in storage granules. The accumulation of acetylcholine in PC12 granules, but not acetylcholine synthesis, was inhibited by treatment of the cells with any of several inhibitors of energy metabolism. These included nigericin, carbonyl cyanide p-trifluoromethoxyphenylhydrazone, dicyclohexylcarbodiimide, and iodoacetate. Valinomycin alone and oligomycin were without effect. Except for iodoacetate, these agents did not exert their effects on acetylcholine storage by depleting the cells of ATP.

Topics: Acetylcholine; Adenosine Triphosphatases; Animals; Biological Transport; Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; Cell Line; Choline; Dicyclohexylcarbodiimide; Kinetics; Nigericin; Pheochromocytoma; Rats; Valinomycin

Topics: Acetylcholine; Animals; Calcium; Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone; Cell Line; Choline; Clone Cells; Cytoplasmic Granules; Dopamine; Iodoacetates; Kinetics; Nigericin; Pheochromocytoma; Potassium; Rats; Valinomycin