title: Inhibition of cyclic AMP-dependent protein kinase activity by the cardiotonic drugs amrinone and milrinone.
abstract: Amrinone and milrinone are new cardiotonic drugs that have potent inotropic and vasodilatory properties. The mechanism of action of these agents is controversial, but the positive inotropic component is thought to be due to the inhibition of phosphodiesterase. Because amrinone and milrinone have been shown to be involved primarily in cyclic AMP-mediated processes, we examined the effect of these agents on cyclic AMP-dependent protein kinase. The results indicate that amrinone and milrinone inhibit cyclic AMP-dependent protein kinase activity by competing with ATP but not cyclic AMP binding sites. Dissociation constants (Ki) of amrinone and milrinone for ATP binding sites on protein kinase were calculated to be 100-300 microM and 842 microM, respectively. The phosphodiesterase inhibitor isobutylmethylxanthine (1 mM) had no effect on protein kinase activity. Amrinone and milrinone inhibited the catalytic subunit of protein kinase to the same degree as the holo-enzyme by competitively inhibiting the binding of ATP. Amrinone and milrinone had no effect on phospholipid-sensitive, calcium-dependent protein kinase indicating that there may be differences in the ATP binding sites on these two protein kinases. Inhibition of cyclic AMP-dependent protein kinase by amrinone and milrinone occurs at concentrations higher than those used clinically. However, because amrinone and milrinone are lipophilic drugs, they may be useful tools for the investigation of protein kinase mediated reactions.
mesh_terms: D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000378:metabolism; D000676:Amrinone / Q000494:pharmacology*; D000818:Animals; D002316:Cardiotonic Agents / Q000494:pharmacology*; D000242:Cyclic AMP / Q000037:antagonists & inhibitors; D004285:Dogs; D066298:In Vitro Techniques; D020105:Milrinone; D009132:Muscles / Q000201:enzymology; D011485:Protein Binding / Q000187:drug effects; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D047428:Protein Kinase Inhibitors; D011728:Pyridones / Q000494:pharmacology*
chemical_list: D002316:Cardiotonic Agents; D047428:Protein Kinase Inhibitors; D011728:Pyridones; D000255:Adenosine Triphosphate; D000242:Cyclic AMP; D011493:Protein Kinase C; D020105:Milrinone; D000676:Amrinone; D015056:1-Methyl-3-isobutylxanthine