Cytochalasin D as the Depressant of Contraction for the Optical Monitoring of Action Potentials in Isolated Rat Atrium

Abstract

Abstract:We used cytochalasin D to reduce contraction-related optical signals by inhibiting muscle contraction for the optical monitoring of action potentials, using a voltage-sensitive dye in isolated rat atrium preparations. The suppression of contractionrelated signals was so strong that we concluded that this chemical is suitable for this purpose.Key words: cytochalasin D, voltage-sensitive dye, rat atrium.Optical techniques for monitoring membrane potential using fast voltage-sensitive dyes are powerful new tools for studying cardiac electrical functions. These methods have several advantages over more conventional electrophysiological techniques, and they are indispensable for understanding the mechanism(s) behind the generation and maintenance of cardiac arrhythmias, in which reentry and/or abnormal automatism may take part [1,2].Using a voltage-sensitive merocyanine-rhodanine dye together with a 16 × 16 or 12 × 12 element photodiode array, we recorded optical action potentials (i.e., action potential-related optical signals) simultaneously from many sites, and optically mapped the excitation spread in isolated rat atrial preparations during the abnormal state of atrial rhythm, which we named "tachycardia-like excitation" (TE), evoked by electrical stimulation [3][4][5][6]. During TE, the action potentials occur at a much faster rate than in the normal condition, and the physiological pacemaker does not work. We demonstrated that the reentry mechanism took part in most situations of TE.Throughout these studies, the suppression of optical signals resulting from muscle contraction (i.e., artifacts) has been the most serious technical problem for obtaining fine optical action potentials. To reduce contraction-related optical signals, we have used mechanical stretching as well as 2,3-butanedione monoxime (BDM: 20 mM), a chemical that inhibits muscle contraction while having little affect on the electrical activities of the cardiac muscle [2,3]. However, the inhibitory effect of this chemical is not complete, and the optical action potentials obtained were always contaminated with contraction-related signals to some degree. Because optical action potentials always precede contraction-related signals, we could discriminate them by the timing of their appearance. But in some cases, it was difficult to do this when the optical action potential was masked with the contraction-related signal. Furthermore, for an analysis of the precise shape of an action potential, especially the repolarization phase, the elimination of any contraction-related optical signal is indispensable. We have been searching for a new chemical that induces a more effective suppression of the contraction-related signal.Recently, cytochalasin D (Cyto D) has been identified as a chemical that inhibits muscle contraction with a minimal affect on electrical excitation. For the optical recording of the cardiac action potential, this chemical was first applied to canine ventricular muscle [7], then to the heart of developing chick embryos [8], and ...

Optical mapping study of blebbistatin-induced chaotic electrical activities in isolated rat atrium preparations

“…However, the inhibitory effect of BDM is not complete, and the optical action potentials obtained were always contaminated to some degree with contraction-related signals. On the other hand, although the suppression of the contraction-related signals by Cyto D is much stronger than with BDM, we found that the former chemical has an effect on the conduction speed of the excitatory waves [7]. We have therefore been searching for a new chemical which would induce more effective suppression of the contraction-related signal without affecting the action potential and the excitation spread.…”

“…In order to reduce contraction-related optical signals, we used mechanical stretching as well as 2,3-butanedione monoxime (BDM: 20 mM) or cytochalasin D (Cyto D: 20-40 lM) [3][4][5][6][7]. These chemicals inhibit muscle contraction while having little effect on the electrical activities of the cardiac muscle.…”

The mechanical uncoupler blebbistatin is associated with significant electrophysiological effects in the isolated rabbit heart

“…Several methods have been used to overcome this obstacle, ranging from mechanical techniques where the heart is contained within a glass chamber to reduce contractile movement (Salama et al 1987; Efimov et al 1996) to pharmacological methods, in which an excitation–contraction uncoupler (ECU) is used to eliminate myocardial contraction. 2,3‐Butanedione monoxime and cytochalasin‐D are two ECUs with effective uncoupling properties in cardiac models (Biermann et al 1998; Sakai, 2006; Jou et al 2010) and were historically used in optical mapping. However, significant effects on cardiac electrophysiology have been reported (Blanchard et al 1990; Liu et al 1993; Maesako et al 2000; Watanabe et al 2001; Baker et al 2004; Kettlewell et al 2004), which limit their use in optical mapping.…”