Cytochalasin D as excitation-contraction uncoupler for optically mapping action potentials in wedges of ventricular myocardium

Myocardium Immobilization for Repolarization Mapping. Introduction: Cytocha lasin D in tissue bath superfusate inhibits the contraction of isolated thi n trabeculae from canine right ventricle without affecting the intracellula r action potential recorded with glass microelectrode, The purpose of this study was to test whether cytochalasin D could also be used to immobilize p erfused wedges of ventricular muscle without affecting the action potential duration or propagation, and also to determine the optimal concentration a nd time duration of drug in the perfusate, Methods and Results: Using a membrane potential sensitive dye, di-4-ANEPPS, and a high-resolution photodiode optical mapping system at a rate of 1,000 frames/sec, we recorded action potentials on the transmural surface of art erially perfused wedges of muscle from the canine left ventricular free wal l. We also recorded arterial pulse pressure as a surrogate for tissue contr action. Cytochalasin D at greater than or equal to 20 mu mol/L in the perfu sate for greater than or equal to 6 minutes reduced the arterial pulse pres sure to approximately one tenth of its initial value and significantly redu ced or eliminated motion artifacts in the action potentials. A sustained co ncentration of 10 mu mol/L cytochalasin D in the perfusate prevented contra ction from recurring after the tissue was immobilized with an initial conce ntration of 25 mu mol/L. Cytochalasin D had little effect on the action pot ential duration and on its transmural gradient, and did not slow the transm ural velocity of excitation propagation. Conclusion: Cytochalasin D can be used to uncouple excitation and contracti on in perfused canine cardiac muscle for the fluorescent-optical mapping of action potentials without affecting action potential duration or slowing t ransmural propagation.