Role of the cardiac gap junctions in impulse propagation – with special reference to the transitional region between different heart tissues (part 4)
Two separated ventricular muscle strips bridged by a Purkinje fibre were prepared. Two recording electrodes were placed 300 to 500 |J.m apart within the ventricular muscle, the Purkinje fibre, and the Purkinje fibre and the ventricular muscle. Conduction velocity was calculated as a ratio of the distance of the two electrodes to the time difference in upstroke of two action potentials. The preparation was stimulated at 1.0 Hz by suction electrodes placed on the ventricular muscle side.
Statistical analysis was by Student’s t test for paired samples and differences were considered to be significant at P<0.01.
Concentration of heptanol: Heptanol was used to induce electrical cell-to-cell decoupling because it dramatically decreases electrical conductance of the cardiac gap junctions , decreases conduction velocity and increases electrical specific resistance of the cardiac gap junctions. At a concentration range from 0.1 to 1.0 mM, heptanol did not show any effect on maximum diastolic potential, slope of diastolic slow depolarization of the sinus node cell pacemaker potential, resting membrane potential, maximal velocity (Vmax), or action potential duration of atrial, Purkinje fibre and ventricular muscle cells.
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.
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