Role of the cardiac gap junctions in impulse propagation – with special reference to the transitional region between different heart tissues (part 7)
Five minutes after application of 0.5 mM heptanol, the histogram and the CV recorded from the sinus node were almost the same as those under control conditions, while those recorded from the atrium were markedly deviated and raised (Figure 4b). Conduction block was often observed. Changes in CV over time: Changes in CV after application of heptanol (1.0 mM) in the sinus node (S1-S2), the atrium (A1-A2) and between the sinus node and the atrium (S-A) are shown in Figure 6. A marked increase in CV was observed in the atrium on S-A conduction; however, CV in A1-A2 was more resistant to change. The dose-dependent effect of hep-tanol on the CV is shown in Figure 6d. At a lower concentration of 0.1 or 0.5 mM, an increase in CV in the atrium on S-A conduction was also marked compared with that in S2 on S1-S2 and A2 on A1-A2 conduction. As shown in Figure 5, heptanol 0.1 to 1.0 mM decreased the conduction velocity within the ventricular muscle without a significant change in Vmax. These phenomena were reversible. On the contrary, heptanol over 3 mM decreased conduction velocity and Vmax, and significantly decreased action potential duration at the 30%, 50% and 90% levels of repolarization. These results were also obtained in the Purkinje fibre. Therefore, in this study heptanol was used at concentration range from 0.1 to 1.0 mM.
Figure 5 Effect of heptanol 0.1 to 1.0 mM (circles), and 3 to 5 mM (triangles) on the correlation between maximal velocity (Vmax) and conduction velocity in right ventricular muscle of guinea-pig heart. Each point was obtained within 20 mins after application of hep-tanol. Vmax and conduction velocity are relative values (where control =1.0)
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