sq-23377 and 4-bromotetramisole

Tyrosine phosphorylation has been shown to participate in the signal cascade after receptor stimulation with neurotransmitters and neurotrophins. However, the role of tyrosine phosphorylation in the process(es) of neurotransmitter release has not been well established. The effects of orthovanadate (Na3VO4), an inhibitor of protein-tyrosine phosphatases, on cytosolic free Ca2+ concentrations ([Ca2+]i), phosphotyrosine accumulation and noradrenaline (NA) release in neurosecretory PC12 cells were investigated. Addition of Na3VO4 enhanced ionomycin-stimulated [3H]NA release in a concentration-dependent manner, although Na3VO4 alone had no effect. Na3VO4 also enhanced [3H]NA release induced by P2 receptor stimulation with adenosine 5'-O-(3-thiotriphosphate) (ATPgammaS) or by depolarization with 50 mM KCl, which stimulated a [Ca2+]i increase. A cell permeable inhibitor of protein-tyrosine phosphatases, L-p-bromotetramisole oxalate, at 0.3 mM enhanced ionomycin-stimulated [3H]NA release, although pervanadate had no effect. Addition of 5 mM Na3VO4 stimulated phosphotyrosine accumulation in several protein bands such as p130cas, but did not increase [Ca2+]i in PC12 cells. These findings suggest that the tyrosine phosphorylation pathway regulates Ca2+-stimulated NA release without changes of [Ca2+]i in PC12 cells.

Topics: Animals; Calcium; Intercellular Signaling Peptides and Proteins; Intracellular Membranes; Ionomycin; Ionophores; Norepinephrine; Osmolar Concentration; PC12 Cells; Peptides; Phosphorylation; Rats; Tetradecanoylphorbol Acetate; Tetramisole; Tyrosine; Vanadates; Wasp Venoms