EDITORIAL COMMENTARY Pharmacological elimination of motion artifacts during optical imaging of cardiac tissues: Is blebbistatin the answer? Danshi Li, MD, PhD,* Stanley Nattel, MD † From the *Cardiovascular Knowledge Center, Discovery Toxicology, Bristol Myers Squibb Pharmaceutical Research Institute, Pennington, New Jersey, and † Montreal Heart Institute, Université de Montréal, and Department of Pharmacology and Therapeutics, McGill University, Montreal, Quebec, Canada. Since the first measurements of action potentials with voltage-sensitive dyes from the epicardial surface of the frog heart by Salama and Morad, 1 the field of optical im- aging of cardiac electrical activity has evolved dramatically from cellular 2 and subcellular levels to tissue 3 and whole heart 4 physiology, thanks to rapid advancement in optical technology. While optical techniques have been used prin- cipally to map cardiac electrical activity on the heart sur- face, 5 fiber-optic probes that enable simultaneous intramural optical recordings at multiple sites in the heart have also been developed. 6 High-resolution optical recording of elec- trical activity using fluorescent dyes provides simultaneous noncontact recording of action potentials from multiple ad- jacent sites at various scales of resolution in the whole heart and multicellular cardiac tissue preparations. Because the number of photodetectors may be increased without incur- ring increased injury to the tissue, optical methods enable high spatiotemporal resolution of electrical activity that is unattainable by conventional techniques. Another advan- tage of optical methods is the ability to obtain direct detec- tion of repolarization simultaneously with recording of ac- tivation by dynamic sampling of transmembrane potential changes, as compared with conventional mapping, which provides indirect data on repolarization that is calculated from extracellular electrograms. Accordingly, high-resolu- tion optical mapping has become a common research tool in basic cardiac electrophysiology, especially in the investiga- tion of electrophysiologic mechanisms by which conven- tional electrical recordings are hampered by inadequate res- olution or by a lack of precise information on repolarization. In spite of the growing application of optical mapping to cardiac electrophysiology, many technical problems persist and hamper the utility of this technique. Particularly prob- lematic are muscle contractions and associated heart wall motion, which distort optical recordings, the so-called mo- tion artifacts. Various techniques have been used to reduce motion artifacts including reduced extracellular calcium content, physically restraining the heart, 7 and offline anal- ysis techniques of the second derivative of the optical sig- nal. 8 Yet all of these approaches have significant limita- tions. One widely used approach to reduce motion artifacts involves the pharmacological uncoupling of cardiac excita- tion from contraction with an excitation-contraction uncou- pler (ECU), with such agents as 2,3-butanedione monoxime (BDM) and cytochalasin-D (cyto-D). BDM is a noncom- petitive inhibitor of myosin ATPase that is an effective ECU but has been shown to have significant effects on potassium and calcium currents, intracellular calcium handling, and action potential properties at concentrations that inhibit car- diac muscle contraction. 9 –11 Cyto-D is an agent that impairs F-actin filament polymerization and is considered to be a better ECU than BDM. Although cyto-D has negligible effects on action potentials in canine left ventricular wedge preparations, 12 it alters action potential properties in rabbits and mice and affects intracellular calcium handling in mice. 10,11,13 Therefore, both BDM and cyto-D impede the normal processes of excitation and recovery and are not ideal ECUs for optical mapping. In this issue of Heart Rhythm, Fedorov et al 14 report on the properties of a new ECU, blebbistatin (BB). BB is a recently identified selective and specific small molecule inhibitor of the ATPases associated with class II myosin isoforms in an actin-detached state. 15–17 BB inhibits only nonmuscle and skeletal muscle myosin isoforms (IC50 = 0.5–5 M) and is a poor inhibitor of other members of the myosin family. 15,16 In the carefully conducted study by Fedorov et al, 14 the authors tested whether BB could be used as an effective ECU to immobilize different cardiac preparations without affecting electrophysiological param- eters and intracellular calcium cycling. They examined the specificity and potency of BB by studying its dose-depen- dent effects on contraction and cardiac electrophysiological parameters in Langendorff-perfused rabbit hearts, isolated rabbit right ventricles and right atria, and single rat ventric- ular myocytes. The authors combined conventional electro- cardiogram (ECG) recording, surface electrogram measure- ment, microelectrode recording, and optical imaging with Address reprint requests and correspondence: Danshi Li, M.D., Ph.D., Cardiovascular Knowledge Center, Discovery Toxicology, Bristol Myers Squibb Pharmaceutical Research Institute, Pennington, NJ. E-mail address: danshi.li@bms.com. 1547-5271/$ -see front matter © 2007 Heart Rhythm Society. All rights reserved. doi:10.1016/j.hrthm.2007.01.013