Identification of the hyperpolarization-activated inward current in young embryonic chick heart myocytes.
Whole-cell voltage-clamp experiments were performed to examine the underlying currents flowing during the pacemaker potential of spontaneously-beating embryonic chick ventricles. The holding potential was -30 mV. Long-duration (3 s) hyperpolarizing pulses were applied to -40 to -120 mV, in increments of 10 mV. A marked hyperpolarization-activated inward current (If) was produced. In cells from 3-day-old hearts, the threshold potential for the inward current was -50 to -60 mV. In 17-day-old cells, there was almost no If current. At -120 mV, the inward current was -93.8 +/- 6.3 pA (n = 5) in 3-day-old cells and -15.7 +/- 2.8 pA (n = 5) in 17-day-old cells. The average capacitances were 10.1 +/- 2.0 pF (n = 17) in 3-day-old cells, and 6.9 +/- 1.2 pF (n = 14) in 17-day-old cells. The reduction of If paralleled the decrease in spontaneous activity. In the presence of 3 mM CsCl, the inward current was blocked completely, and the tail current was reduced. In addition, 3 mM CsCl depressed the spontaneous action potentials and had a negative chronotropic effect. These results indicate that the hyperpolarization-activated inward If current exists in young embryonic chick heart cells, and decreases during development. This If current may contribute somewhat to the electrogenesis of the pacemaker potential.
Department of Physiology and Biophysics, University of Cincinnati, College of Medicine, Ohio 45267-0576.
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H
Satoh
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Sperelakis
D000200:Action Potentials; D000818:Animals; D002478:Cells, Cultured; D002642:Chick Embryo / Q000502:physiology*; D004553:Electric Conductivity; D006321:Heart / Q000196:embryology / Q000502:physiology*; D006352:Heart Ventricles / Q000166:cytology / Q000196:embryology; D009206:Myocardium / Q000166:cytology*; D016276:Ventricular Function