Tetsuro Sakai

Optical mapping of the spread of excitation in the isolated rat atrium during tachycardia-like excitation

Multiple-site optical recording of membrane potential activity, using the voltage-sensitive merocyanine-rhodanine dye NK2761 and a multiple-element photodiode array, was employed to monitor action potentials in an isolated rat atrial preparation. The events of tachycardia-like excitation (TE) were evoked by electrical stimulation. The conduction pattern of excitation was assessed optically by timing the feet of optical action potentials, then maps of excitation spread patterns were made. The excitatory waves often rotated around the blocked area including the ostium of the superior vena cava. Other patterns, such as reentry without anatomical obstacles, ectopic pacemaker and more complex patterns, were sometimes observed. Optical mapping during the initiation phase of TE indicated that the decrease of the conduction velocity and the appearance of blocked areas contributed the establishment of TE. On the basis of the characteristics of TE, it is suggested that TE is a metastable state of atrial rhythm. TE appears to be analogous to atrial flutter.

Functiogenesis of cardiac pacemaker activity

Throughout our investigations on the ontogenesis of the electrophysiological events in early embryonic chick hearts, using optical techniques to record membrane potential probed with voltage-sensitive dyes, we have introduced a novel concept of “functiogenesis” corresponding to “morphogenesis”. This article gives an account of the framework of “functiogenesis”, focusing on the cardiac pacemaker function and the functional organization of the pacemaking area.

Chaotic Electrical Excitation in the Rat Atrium Revealed by Optical Mapping Studies

Spatiotemporal patterns of chaotic electrical excitation-waves in isolated rat atrial preparations were mapped by multiple-site optical recording methods using a multi-element photodiode array together with a fast merocyanine-rhodanine voltage-sensitive dye. Tachycardia-like excitation was evoked by electrical stimulation, then maps of the excitation spread patterns were constructed. In these maps, event-to-event variations are always observed. The event-to-event variations seem to result from the physiologically trivial difference(s) in the initial conditions. This nature of “complex system” strongly supports the idea that tachycardia-like excitation is an example of the functional “self organizing systems”. Although, at the present stage, it is quite difficult to analyze this phenomenon quantitatively, we consider the tachycardia-like excitation observed here as the “physiology-specific attractor”.