Pacemaker current i(f) in adult canine cardiac ventricular myocytes
Abstract
1. Single cells enzymatically isolated from canine ventricle and canine Purkinje fibres were studied with the whole-cell patch clamp technique, and the properties of the pacemaker current i(f) compared. 2. Steady-state i(f) activation occurred in canine ventricular myocytes at more negative potentials (-120 to -170 mV) than in canine Purkinje cells (-80 to -130 mV). 3. Reversal potentials were obtained in various extracellular Na+ (140, 79 or 37 mM) and K+ concentrations (25, 9 or 5.4 mM) to determine the ionic selectivity of i(f) in the ventricle. The results suggest that this current was carried by both sodium and potassium ions. 4. The plots of the time constants of i(f) activation against voltage were 'bell shaped' in both canine ventricular and Purkinje myocytes. The curve for the ventricular myocytes was shifted about 30 mV in the negative direction. In both ventricular and Purkinje myocytes, the fully activated I-V relationship exhibited outward rectification in 5.4 mM extracellular K+. 5. Calyculin A (0.5 microM) increased i(f) by shifting its activation to more positive potentials in ventricular myocytes. Protein kinase inhibition by H-7 (200 microM) or H-8 (100 microM) reversed the positive voltage shift of i(f) activ...Continue Reading
Citations
Characterization of the heart rate-lowering action of ivabradine, a selective I(f) current inhibitor
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