CYCLIC-AMP ACCUMULATION INDUCES A RAPID DESENSITIZATION OF THE CYCLIC AMP-DEPENDENT PROTEIN-KINASE IN MOUSE STRIATAL NEURONS

Striatal neurons from the mouse brain embryo grown in primary culture express high levels of cyclic AMP (cAMP)-dependent protein kinase (PKA) activity. To study the modulation of PKA in intact neurons, a rapid method based on Zn2+-protein precipitation was developed. This strategy allowed analysis of the stimulation of PKA under conditions of intracellular cAMP concentration increases. Whereas increases up to 1-mu-M lead to an activation, large and sustained accumulations of cAMP result in a loss of the enzyme activity. With 8-bromo-cAMP (8-Br-cAMP) at 100-mu-M, the PKA refractoriness occurs within 2 min. It is rapidly reversible because incubation of treated neurons in fresh medium leads to a complete recovery of PKA activity within 30 min. The decrease in assayable PKA does not involve an activation of phosphatases because the histone dephosphorylation rate is not affected by 8-Br-cAMP treatment. Finally, not only 8-Br-cAMP- but also forskolin- and vasoactive intestinal peptide-induced increases in intracellular cAMP concentration can lead to the PKA desensitization. Altogether, these data unravel a new mechanism of PKA regulation.