A possible role of the phosphorylation of synaptic membrane proteins in the control of calcium ion permeability.

Incubation of synaptosomes under conditions which result in complete phosphorylation of membrane bound accepter proteins does not affect the permeability to Na+ or K+ as measured by a spectrophotometric method. This technique was not, however, sensitive enough to determine permeability to Ca2+ which was thus estimated, using 45Ca2+. It was found that although phosphorylation did not affect the equilibrium binding of 45Ca it did lower the rate of both Ca2+ uptake and efflux. The most likely interpretation of these results is that phosphorylation of proteins in the synaptic membrane lowers the permeability of the membrane to Ca2+. This could have a role in the regulation of synaptic transmission.