Conditions restricting depolarization-dependent calcium influx in synaptosomes reveal a graded response of P96 dephosphorylation and a transient dephosphorylation of P65

J Neurochem. 1991 Jun;56(6):2039-47. doi: 10.1111/j.1471-4159.1991.tb03464.x.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acetylcholine / metabolism
  • Animals
  • Calcium / metabolism*
  • Choline / pharmacology
  • Culture Media
  • Electrophysiology
  • Molecular Weight
  • Phosphoproteins / chemistry
  • Phosphoproteins / metabolism*
  • Phosphorylation
  • Potassium / pharmacology
  • Rats
  • Synaptosomes / metabolism*
  • Synaptosomes / physiology
  • Veratridine / pharmacology


  • Culture Media
  • Phosphoproteins
  • Veratridine
  • Choline
  • Acetylcholine
  • Potassium
  • Calcium