title: Properties of the transient outward current in rabbit sino-atrial node cells.
abstract: The electrophysiological properties of the transient outward current were investigated in voltage-clamped single cells from the rabbit sino-atrial node. To make a regional comparison, some experiments were repeated in atrial myocytes. The current-voltage relationship showed a characteristic outward rectification with an activation threshold of -30 mV. External 4-aminopyridine (0.01-5 mM) inhibited this current in a dose-dependent manner (IC50 = 0.28 mM, Hill coefficient = 1.38). The steady-state inactivation exhibited a half-maximum voltage of -35 mV and a slope factor of -.4 mV. The current density of the transient outward current was 6.3 +/- 0.5 pA/pF in sino-atrial node cells and 12.3 +/- 1.2 pA/pF in atrial cells. The inactivation time constant was faster in sino-atrial node cells (time constants 4.2 +/- 0.5 and 26.0 +/- 0.6 ms, respectively, for the fast and slow components) than in atrial cells (9.7 +/- 1.2 and 44.8 +/- 3.2 ms, respectively). Recovery from inactivation was much faster in sino-atrial node cells (time constants 44.7 +/- 9.0 ms) than in atrial cells (time constants 1.39 +/- 0.32 and 6.70 +/- 0.1 s, respectively, for the fast and slow components). These results suggest that the kinetic properties, as well as the current density, of the transient outward current differs between sino-atrial node and atrial cells. Taking the current density of Ito at +10 mV as 2.5 +/- 0.3 pA/pF gives a total Ito of approximately 100 pA at the peak of the action potential in rabbit sino-atrial node cells. The action potential duration was increased by 24.8 +/- 1.3% by 0.5 mM 4-AP. Thus, Ito may contribute significantly to the repolarization phase in mammalian sino-atrial node cells.
authors.affiliation: Heart Institute of Japan, Tokyo Women's Medical University, Japan.
authors.forename: K
authors.initials: K
authors.lastname: Uese
authors.forename: N
authors.initials: N
authors.lastname: Hagiwara
authors.forename: T
authors.initials: T
authors.lastname: Miyawaki
authors.forename: H
authors.initials: H
authors.lastname: Kasanuki
mesh_terms: D015761:4-Aminopyridine / Q000494:pharmacology; D000818:Animals; D006321:Heart / Q000187:drug effects / Q000502:physiology*; D006325:Heart Atria; D066298:In Vitro Techniques; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology*; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology; D011817:Rabbits; D012849:Sinoatrial Node / Q000166:cytology / Q000187:drug effects / Q000502:physiology*
chemical_list: D015221:Potassium Channels; D015761:4-Aminopyridine