Role of the cardiac gap junctions in impulse propagation – with special reference to the transitional region between different heart tissues (part 3)
Transmembrane action potentials were recorded with two or three microelectrodes placed 300 |J.m apart (Figure 1a). A histogram and trendgraph of variation in the interval of action potentials recorded for a period of 20 s were computed by signal processor (7T18A, NEC Sanei Instruments, Ltd, Tokyo, Japan). The coefficient of variation of the action potential interval (CV) was determined by the formula
where m is the mean value of the action potential interval and SD is the standard deviation. CV was taken as an index of synchronization or desynchronization of electrical activity; that is, an increase in CV indicates desynchronization.As shown in Figure 1a, the electrode named as the ‘key electrode’ was placed at the centre of the sinus node preparation (S1), at the centre of the atrium preparation (A1) or at the sinus node of the sinus node-atrium preparation (S). The CV recorded from each key electrode was not significantly changed after an application of heptanol (0.1 to 1.0 mM). When the CV in the key electrode was significantly changed by heptanol in comparison with control values, these data were excluded from statistical analysis.
Figure 1a Schematic drawing of positions of recording electrodes in preparations of the sinus node region (S1-S2), the sinus node-atrium (S-A) and the atrial region (A1-A2). Filled circles represent key electrodes, open circles represent other electrodes. b Schematic drawing of positions of recording electrodes in a preparation of ventricular muscle strips bridged by a Purkinje fibre. Stimulation was carried out by suction electrodes. P-P Conduction velocity within the Purkinje fibre; P-V Conduction velocity between Purkinje fibre and ventricular muscle; V-V Conduction velocity within ventricular muscle
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