Characterisation of cAMP-dependent protein kinase isoforms in the brain ofthe crab Chasmagnathus

In the crab Chasmagnathus learning model, systemic administration of cAMP a nalogues that are specific activators or inhibitors of cAMP-dependent prote in kinase (PKA) proved to respectively facilitate or impair long-term reten tion. The aims of the present work were to analyse PKA activity distributio n in the crab brain and to characterise PKA isoforms. The neuropils from th e eyestalk showed higher levels of induced PKA activity when compared with other neuropils of the central nervous system. Two PKA isoforms, homologous to mammalian PKA I and PKA II, were detected from central brain protein ex tracts using DEAE chromatography. Only PKA II was found in lateral protocer ebrum extracts, suggesting a role of this isoform in the processing of visu al inputs and in the integration of this information with other sensory inp uts. PKA I was observed to be ten-fold more sensitive to cAMP than PKA II. cGMP induced a high activation of both PKA isoforms. similar to that obtain ed with cAMP. PKA I showed a two-fold greater sensitivity for cGMP than PKA II. An autophosphorylation assay was per formed and a protein of 55 kDa, c orresponding to phosphorylated R II regulatory subunit, was detected. The p resence of a PKA I isoform with high sensitivity for cAMP in the central br ain suggests a role of this subtype in long-term memory.