Modulation of protein kinase C activity by amiodarone and desethylamiodarone.

Protein Kinase C (PKC), a Ca(2+)-dependent and phospholipid activated enzyme, regulates a variety of intracellular and extracellular signals across the neuronal membrane. A number of Ca(2+)-dependent enzymes are PKC substrates. PKC activity is modulated by lipophilic compounds including calmodulin inhibitors. Amiodarone, an antiarrhythmic drug is associated with some neurologic and pulmonary side effects and has been shown to interact with calmodulin. The present study describes the effects of amiodarone and desethylamiodarone, a major metabolite of amiodarone, on PKC activity. PKC was partially purified from rat brain on an anion exchange column (DE-52). The interaction of amiodarone and desethylamiodarone with PKC was studied as a measure of altered protein phosphorylation and 3H-phorbol 12, 13-dibutyrate (PDBu) binding. Desethylamiodarone significantly inhibited phosphatidylserine, diacylglycerol and Ca2+ stimulated PKC activity with IC50 of 30 microM. However, amiodarone had no significant effect on PKC activity. Both amiodarone and desethylamiodarone altered the 3H-PDBu binding to PKC and the effect was biphasic. The Scatchard analysis of 3H-PDBu binding to PKC revealed that at lower concentrations (5 microM), amiodarone and desethylamiodarone increased 3H-PDBu binding to PKC with decreased affinity. Whereas, at higher concentrations (greater than 30 microM) these drugs decreased the 3H-PDBu binding. In the presence of Ca2+, phosphatidylserine and PDBu (120 nM) no significant stimulation was observed with low concentrations of amiodarone and desethylamiodarone. However, at high concentrations (50 microM), desethylamiodarone inhibited the PDBu stimulated PKC activity. These data clearly demonstrate that desethylamiodarone a metabolite of amiodarone is a potent inhibitor of PKC activity.(ABSTRACT TRUNCATED AT 250 WORDS)