SYNAPTOSOMAL AMINO-ACID RELEASE - EFFECT OF INHIBITING PROTEIN PHOSPHATASES WITH OKADAIC ACID

The protein phosphatase inhibitor okadaic acid was used to investigate the role of protein phosphatases in regulating the release of amino a cids from synaptosomes. Okadaic acid increased the basal release of th e amino acids glutamate, aspartate and GABA. The effect was specific i n that taurine was not released by either Kcl or okadaic acid and ther e was no synaptosomal lysis or change in ATP/ADP ratios in the presenc e of okadaic acid. The okadaic acid-stimulated release of amino acids was, however, only a small proportion of that produced by KCl depolari sation. Since okadaic acid raised synaptosomal protein phosphorylation levels to those equivalent to that produced by KC] depolarisation, it is unlikely therefore that there is a direct causal relationship betw een protein phosphorylation and the release of amino acids. Neverthele ss, that release of amino acids from synaptosomes can be elevated unde r basal conditions by okadaic acid treatment does suggest that okadaic acid-sensitive protein phosphatases have a modulatory role in this pr ocess.