Depolarization of cultured rat brain neurons preloaded with 3H-dopamine provokes a transient (t1/2= 9.6 sec), Ca2+-dependent release of the labeled neurotransmitter from cells. In parallel, the amount of 32Pi incorporated into a protein of apparent molecular weight of 43000 increased whereas the phosphorylation of a protein with an apparent molecular weight of 55000 daltons decreased. The time course of the change in phosphorylation pattern was examined. The depolarization-induced phosphorylation of the 45000 protein and dephosphorylation of the 55000 dalton protein consisted of an initial, rapidly terminating phase (t1/2= 5 sec), and of a slow, Ca2+-independent phosphorylation of both proteins which persisted during maintained depolarization. The depolarization-evoked changes in the neuronal protein phosphorylation were dependent on the extracellular Ca2+ concentration (half saturation at 0.4-0.5 mM Ca2+). These data indicate that the entry of Ca2+into the depolarized cells induces rapid phosphorylation-dephosphorylation activities. These processes terminate within 10 sec, concurrently with the depression of neurotransmitter release.
|Number of pages||9|
|Journal||Journal of Basic and Clinical Physiology and Pharmacology|
|State||Published - Jul 1991|