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.
Satoh
H
H
Department of Physiology and Biophysics, University of Cincinnati, College of Medicine, Ohio 45267-0576.
Sperelakis
N
N
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