title: Existence of a transient outward K(+) current in guinea pig cardiac myocytes.
abstract: A novel transient outward K(+) current that exhibits inward-going rectification (I(to.ir)) was identified in guinea pig atrial and ventricular myocytes. I(to.ir) was insensitive to 4-aminopyridine (4-AP) but was blocked by 200 micromol/l Ba(2+) or removal of external K(+). The zero current potential shifted 51-53 mV/decade change in external K(+). I(to.ir) density was twofold greater in ventricular than in atrial myocytes, and biexponential inactivation occurs in both types of myocytes. At -20 mV, the fast inactivation time constants were 7.7 +/- 1.8 and 6.1 +/- 1.2 ms and the slow inactivation time constants were 85.1 +/- 14.8 and 77.3 +/- 10.4 ms in ventricular and atrial cells, respectively. The midpoints for steady-state inactivation were -36.4 +/- 0.3 and -51.6 +/- 0.4 mV, and recovery from inactivation was rapid near the resting potential (time constants = 7.9 +/- 1.9 and 8.8 +/- 2.1 ms, respectively). I(to.ir) was detected in Na(+)-containing and Na(+)-free solutions and was not blocked by 20 nmol/l saxitoxin. Action potential clamp revealed that I(to.ir) contributed an outward current that activated rapidly on depolarization and inactivated by early phase 2 in both tissues. Although it is well known that 4-AP-sensitive transient outward current is absent in guinea pig, this Ba(2+)-sensitive and 4-AP-insensitive K(+) current has been overlooked.
authors.affiliation: Department of Medicine, Montreal Heart Institute and University of Montreal, Montreal, Quebec, Canada H3C 3J7. gli@hsc.vcu.edu
authors.forename: G R
authors.initials: GR
authors.lastname: Li
authors.forename: B
authors.initials: B
authors.lastname: Yang
authors.forename: H
authors.initials: H
authors.lastname: Sun
authors.forename: C M
authors.initials: CM
authors.lastname: Baumgarten
mesh_terms: D015761:4-Aminopyridine / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D001464:Barium / Q000494:pharmacology; D002478:Cells, Cultured; D006168:Guinea Pigs; D006321:Heart / Q000502:physiology*; D006325:Heart Atria; D006352:Heart Ventricles; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009206:Myocardium / Q000166:cytology; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000494:pharmacology; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*
chemical_list: D015221:Potassium Channels; D001464:Barium; D015761:4-Aminopyridine; D011188:Potassium