Phosphorylase kinase phosphorylates a brain protein which is influenced by repetitive synaptic activation

Abstract

SYNAPTIC systems from mammalian brain can now be studied in situ using a brain slice preparation which displays most of the electrophysiological characteristics observed in intact preparations^1,2. We have been particularly interested in analysis of long-term potentiation (LTP), a marked and quasi-permanent increase in synaptic efficacy which is found in the hippocampal formation following a brief (1 s) train of repetitive stimulation^3–6. Previous work from this laboratory demonstrated a strong correlation between induction of such LTP and the apparent phosphorylation of a 40,000 molecular weight protein in synaptic plasma membranes (SPM)^7,8. Both LTP and the stimulation-dependent changes in the 40,000-MW protein were dependent on calcium and this cation has also recently been shown (ref. 9 and unpublished observations) to enhance the endogenous phosphorylation of a protein with a molecular weight of ∼40,000. If potentiation and the phosphorylation of the 40,000-MW protein are related, with calcium being required for both, then it is possible that a calcium-dependent protein kinase might be an intermediary enzyme in the two processes. We have therefore investigated the effect of exogeneous phosphorylase kinase (PBK; EC 2.7.1.38), a calcium-sensitive enzyme found in brain^10,11, on the phosphorylation of the 40,000-MW protein. Since several laboratories have demonstrated cyclic AMP-dependent phosphorylation of several SPM proteins^12–15, it was also of interest to test for the possibility that this nucleotide might be involved in the phosphorylation of the 40,000-MW protein. We report here that PBK produces a marked and highly specific phosphorylation of the 40,000-MW protein that we have previously shown to be affected by high frequency potentiating stimulation.