Role of the cardiac gap junctions in impulse propagation – with special reference to the transitional region between different heart tissues (part 9)
It has been reported that heptanol closes gap junction channels , and decreases gap junction conductance and conduction velocity in cardiac muscle. According to the cable theory of membrane properties, conduction velocity is influenced by Vmax and membrane resistance (Rm). Therefore, an examination of gap junction-dependent conduction velocity should confirm that heptanol at a given concentration has no effect on Vmax and Rm. In the present study, at relatively high concentrations (over 3 mM) heptanol depolarized the membrane, decreased Vmax and shortened the action potential duration of Purkinje fibre and ventricular muscle. This observation indicates that heptanol at high concentrations affects Rm and intracellular concentrations of sodium, potassium and calcium of the plasma membrane.However, at the relatively low concentration used in this experiment (0.1 to 1.0 mM), heptanol did not affect resting membrane potential; Vmax; action potential duration of atrial muscle, Purkinje fibre or ventricular muscle; maximum diastolic potential; or slope of diastolic slow depolarization of pacemaker potential of the sinus node; however, it dramatically decreased conduction velocity without decreasing Vmax, as shown in Figure 5. These effects of heptanol at lower concentration were reversible. Our previous results showed that 0.5 mM heptanol reversibly increased specific resistance of the gap junction of rabbit ventricular muscle from 130.2±9.2 to 338.3±53.9 Qcm (mean ± SEM) in association with a decrease in conduction velocity from 0.76±0.09 to 0.28±0.06 m/s (mean ± SEM) within 30 mins with no effect on Vmax . These results concur that heptanol at the relatively low concentration used here affects mainly the gap junction protein (connexin) and closes the gap junction channels, without affecting Rm and intracellular concentrations of sodium, potassium and calcium currents of the plasma membrane. You will always enjoy getting clomiphene 50 mg cialis professional, being 100% sure you are safe.