Effect of moracizine and ethacizine on receptors of potential-operated calcium channels and calcium-binding proteins.

The action of two antiarrhytmic drugs, moracizine (MOR, CAS 31883-05-3) and ethacizine (ETHA, CAS 33414-33-4) on receptors of potential-operated CA-channels has been investigated. ETHA binding to verapamil receptors was more effective than that of MOR (IC50 = 0.53 +/- 0.08 mumol/l, respectively). The Hill coefficient for ETHA binding was similar to that of verapamil (0.64 +/- 0.09 and 0.60 +/- 0.10, respectively). Interaction of ETHA and MOR with dihydropyridine receptors in concentrations up to 10 mumol/l was similar that of verapamil, however, MOR was less potent. MOR and ETHA did not interact with calmodulin and troponin C at concentrations up to 100 mumol/l. The influence of MOR and ETHA on enzymes dependent on Ca-binding proteins (phosphodiesterase and actomyosin ATPase) was not observed up to 100 mumol/l. Comparison of clinical and electrophysiological data with these results allows the conclusion that ETHA exerts Ca-blocking effects by the interaction with verapamil receptors on potential-operated Ca-channels.