Detalle de: CONDITIONS RESTRICTING DEPOLARIZATION-DEPENDENT CALCIUM INFLUX IN SYNAPTOSOMES REVEAL A GRADED RESPONSE OF P96-DEPHOSPHORYLATION AND A TRANSIENT DEPHOSPHORYLATION OF P65

Temporal changes in the phosphorylation level of synaptosomal phosphoproteins following depolarization of synaptosomes were investigated under conditions restricting calcium influx. High‐K + depolarization in media of low [Na + ] o (32 m M during preincubation and depolarization) at pH 6.5 resulted in a pronounced fall in the cytosolic free calcium concentration transient, and in a reduction in the initial K + ‐stimulated 45 Ca 2+ uptake and endogenous acetylcholine release relative to the values obtained with control synaptosomes (preincubated and depolarized in Na + ‐based media). This reduction was paralleled by a decrease in the rate of dephosphorylation of the synaptosomal protein P96. A slower dephosphorylation of P96 also was observed on exposure to 20 μ M veratridine at 0.5 m M external calcium. Our results indicate that, similar to synapsin I phosphorylation, P96 dephosphorylation shows a graded response to the amount of calcium entering the presynaptic terminal. Depolarization of synaptosomes under conditions restricting the influx of calcium revealed a transient dephosphorylation (reversed within 10 s) of the phosphoprotein P65. The possible significance of this finding to the process of neurotransmitter release is discussed.