One‐Trial In Vitro Conditioning of Hermissenda Regulates Phosphorylation of Ser‐122 of Csp24

Abstract

The regulation of the intrinsic excitability of a neuron is an important aspect of cellular and synaptic plasticity underlying learning and memory. Various voltage-dependent K(+) channels have been shown to be critical for the modification of membrane excitability. Components of the cytoskeleton have been proposed to contribute to the location, distribution, and function of diverse K(+) channels. However, the mechanisms underlying the regulation of the cytoskeleton by signaling pathways and the role of the cytoskeleton in the induction of intrinsic excitability is not understood. Hermissenda Csp24 is a beta-thymosin-like protein containing multiple actin-binding domains that contributes to intrinsic enhanced excitability produced by Pavlovian conditioning. One-trial in vitro conditioning produces a significant reduction in the A-type transient K(+) current (I(A)) and a depolarized shift in the steady-state activation curve of I(A). Intermediate and long-term enhanced excitability produced by one-trial conditioning is also dependent on the expression and phosphorylation of Csp24. Blocking the expression of Csp24 with an antisense oligonucleotide inhibits the development of intermediate-term enhanced excitability and the concomitant reduction in I(A) normally produced by one-trial in vitro conditioning. In this report using two-dimensional gel PAGE and electrospray mass spectrometry, we have identified two phosphorylation sites on Csp24. Using phospho-specific antibodies with Western blot analysis and immunoprecipitation procedures we show that one-trial in vitro conditioning results in an increase in the phosphorylation of Ser-122, but not Ser-49 of Csp24.