Dipyridamole stimulates types II cAMP-dependent protein kinase in vitro

Dipyridamole activates in vitro type II CAMP-dependent protein kinase. This agent stimulates the autophosphorylation of the regulatory subunit in the presence of CAMP but not so in the absence of the cyclic nucleotide. The activation was also observed with exogenous substrates such as casein, histone 2A and MAP 2. This stimulation did not seem to be related to the cAMP binding to the R II subunit of the enzyme. Competition binding experiments showed that dipyridamole does not compete with adenosine for the A₁ receptor. The results suggest that the reported regulatory properties of dipyridamole on lipid metabolism (González-Nicolás et al. Int J Biochem 21: 883–888, 1989) might be mediated through a direct action — an activation — on the catalytic subunit of a cAMP-dependent protein kinase.