ISSN:
1471-4159
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Medicine
Notes:
Abstract: Depolarization of intact synaptosomes activates calcium channels, leads to an influx of calcium, and increases the phosphorylation of several neuronal proteins. In contrast, there are two synaptosomal phosphoproteins labeled in intact synaptosomes with 32P1, termed P96 and P 139, which appear to be dephosphorylated following depolarization. Within intact synaptosomes P96 was found in the cytosol whereas P 139 was present largely in membrane fractions. Depolarization-stimulated dephosphorylation was fully reversible and continued for up to five cycles of depolarization/repolarization, suggesting a physiological role for the phenomenon. The basal phosphorylation of these proteins was at least partly regulated by cyclic AMP, since dibutyryl cyclic AMP produced small but significant increases in P96 and P 139 labeling, even in the presence of fluphenazine at concentrations that inhibited calcium-stimulated protein kinases. Depolarization-dependent dephosphorylation was independent of a rise in intracellular calcium, since agents such as guanidine and low concentrations of A23187, which increase intracellular calcium without activating the calcium channel, did not initiate P96 or P 139 dephosphorylation. These agàents did sustain increases in the phosphorylation of a number of other proteins including synapsin I and protein III. The results suggest that the phosphorylation of these two synaptosomal proteins is intimately linked to the membrane potential and that their dephosphorylation is dependent on both the mechanism of calcium entry and calcium itself, rather than simply on a rise in intracellular free calcium.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1471-4159.1987.tb13146.x
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