Toshifumi Watanabe

A practical microcomputer-based mapping system for body surface, precordium, and epicardium☆

Abstract A practical microcomputer-based mapping system is introduced for three different potential mapping applications: (1) an array of 48 AgAgCl electrodes for epicardial mapping, (2) a system of 64 AgAgCl dry electrode for precordial mapping, and (3) an 87-electrode configuration for general body surface potential mapping. The compact, mobile microcomputer system with multiplexing and sample-and-hold techniques makes it possible to construct high-resolution maps from simultaneously sampled ECG potential data in clinical and experimental conditions. It takes only 20–25 min from the beginning of electrode placement to the completion of potential or isochronic map displays on the graphic terminal. Digital magnetic cassette tapes are used as external storage mediums which permit interchange of stored data on a larger computer.

Effects of propafenone on electrical and mechanical activities of single ventricular myocytes isolated from guinea‐pig hearts

1 The effects of propafenone on the transmembrane action potential and sarcomere shortening during twitch contraction were investigated in single ventricular myocytes isolated from guinea‐pig hearts. 2 Propafenone at low concentrations (3–5 × 10−7 m) slightly lengthened action potential duration (APD), but shortened it at higher concentrations. The shortening of APD was accompanied by an attenuation of sarcomere shortening during twitch contraction. 3 Propafenone (>10−6 m) caused a concentration‐dependent decrease in the maximum upstroke velocity () of the action potential. In the presence of propafenone (3 × 10−6 m), trains of stimuli led to an exponential decline in A time constant for the recovery of from the use‐dependent block was 4.8 s. 4 In myocytes treated with propafenone (3 × 10−6 m), the of test action potentials preceded by the conditioning clamp pulses to 0mV was progressively decreased by increasing the duration of single clamp pulse or by increasing the number of multiple brief clamp pulses. 5 These findings suggest that propafenone has use‐dependent inhibitory action on the sodium channel by binding to the channel during both activated and inactivated states, and that the unbinding rate is comparable to that of Class‐I antiarrhythmic drugs with intermediate kinetics. Propafenone may also have an inhibitory action on calcium and potassium channels.

Fluctuations of membrane potential in isolated single ventricular myocytes of guinea-pig upon resumption of oxidative phosphorylation

Electrical and mechanical activities of guinea-pig single ventricular myocytes were investigated under conditions simulating hypoxia-reoxygenation. The localized movement of sarcomere was recorded simultaneously with membrane potential, and analyzed using microcomputer-based image processing. Exposure to 5 mM CN- caused progressive shortening of action potential duration and attenuation of twitch contraction. The myocytes became inexcitable about 30 to 70 min after the CN- treatment. On removal of CN-, the myocytes exhibited periodic miniature membrane depolarizations from the resting potential level (-95 mV). When depolarizations were smaller than 6 mV in amplitude and longer than 500 ms in duration, they were accompanied by localized sarcomere shortening like a propagating contractile wave (unifocal oscillation). Membrane depolarizations of larger amplitude and shorter duration were associated with a more uniform pattern of localized sarcomere shortening (multifocal oscillation). Trains of electrical stimuli applied during the washing out period caused transient augmentation of potential fluctuation and enhancement of synchronization of sarcomere shortening. These results suggest that non-uniform elevation of intracellular calcium concentration on the resumption of oxidative phosphorylation may initiate oscillatory fluctuations of membrane potential leading to abnormal spontaneous excitation.

Microcomputer-based image processing system for measuring sarcomere motion of single cardiac cells

A microcomputer-based image processing system that was developed to obtain contractile properties of single heart cells is described. Cell images were videotaped while action potentials were recorded and were digitized and processed to measure sarcomere length during cell shortening. This system makes it possible to study action potentials and their associated contractions simultaneously.<<ETX>>