Facilitatory Effect of Calmodulin-Dependent Protein Kinase on the K⁺-Current Responses to Dopamine, Acetylcholine, and Phe-Met-Arg-Phe-NH₂ in the Ganglion Cells of Aplysia

Abstract

Formation of either long-term potentiation (LTP) or long-term depression (LTD) of the synaptic transmission is thought to be the primary requirement for learning and memory. These LTP and LTD are usually produced by the activation of various enzymes at both pre- and postsynaptic loci after the transsynaptic stimulation of the receptors. We previously reported that acetylcholine (ACh)-, dopamine (DA)-, histamine (HA)-, and Phe-Met-Arg-Phe-NH₂ (FMRFamide)-induced K⁺-current responses are all mediated by common GTP-binding protein G_i or G₀, irrespective of their kinds of transmitters or types of receptors (Sasaki and Sato 1987). Furthermore, we recently reported that all these K⁺-current responses are markedly depressed by the activation of intracellular protein kinase A or C (Sasaki et al. 1997). At present we are considering the possibility that other kinases, such as calmodulin-dependent protein kinase (CaMK) and protein tyrosine kinase, or various protein phosphatases may also be activated simultaneously after the stimulation of these receptors, producing the primary reactions necessary for the formation of LTP or LTD (Kawasaki et al. 1998). This study examines the role of CaMK activation on the DA-, ACh-, and FMRFamideinduced K⁺-current responses in the ganglion cells of Aplysia, and discusses the possible acting site of this enzyme in the signal-transducing pathway involved in these receptor-induced responses.