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 mM 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 45Ca2+ 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 microM veratridine at 0.5 mM 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.
Gómez-Puertas
P
P
Departamento de Biología Molecular, Centro de Biología Molecular, CSIC-Universidad Autónoma de Madrid, Spain.
Martínez-Serrano
A
A
Blanco
P
P
Satrústegui
J
J
Bogónez
E
E
D000109:Acetylcholine / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002794:Choline / Q000494:pharmacology; D003470:Culture Media; D004594:Electrophysiology; D008970:Molecular Weight; D010750:Phosphoproteins / Q000737:chemistry / Q000378:metabolism*; D010766:Phosphorylation; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D013574:Synaptosomes / Q000378:metabolism* / Q000502:physiology; D014701:Veratridine / Q000494:pharmacology
D003470:Culture Media; D010750:Phosphoproteins; D014701:Veratridine; D002794:Choline; D000109:Acetylcholine; D011188:Potassium; D002118:Calcium