Inhibition of cyclic AMP-dependent protein kinase by somatostatin in slices of mouse brain: dependence on extracellular calcium.

Over a concentration range from 2 to 8 micrograms/ml, cyclic somatostatin inhibited cyclic AMP-dependent protein kinase and cyclic AMP binding activity in slices of mouse brain. An inverse pattern of variation was observed in the activity of phosphoprotein phosphatase. The action on kinase activity was observed in the presence of physiological concentrations of extracellular calcium, but when the concentration of calcium was increased the inhibition of kinase was not observed. These results support the idea that the protein kinase system may be involved in the action of somatostatin in the central nervous system and they are consistent with the hypothesis that somatostatin affects calcium flux.