title: Repolarizing K+ currents in rabbit heart Purkinje cells.
abstract: 1. Electrophysiological experiments on single myocytes obtained from Purkinje fibres and ventricular tissue of adult rabbit hearts were done to compare the contributions of three potassium (K+) currents to the action potentials in these two tissues. 2. In Purkinje cells reductions in extracellular potassium, [K+]o, from normal (5.4 mM) to 2.0 mM resulted in a large hyperpolarization and marked lengthening of the action potential. In ventricular myocytes, these changes were much less pronounced. Voltage clamp measurements demonstrated that these differences were mainly due to a much smaller inward rectifier K+ current, IK1, in Purkinje cells than in ventricular myocytes. 3. Application of 4-aminopyridine (4-AP, 2 mM) showed that all Purkinje cells exhibited a very substantial Ca2+-independent transient K+ outward current, It. 4-AP significantly broadened the early, rapid repolarization phase of the action potential. 4. Selective inhibitors of the fast component, IK, r (MK-499, 200 nM) and the slow component IK,s (L-735821 (propenamide), 20 nM) of the delayed rectifier K+ currents both significantly lengthened the action potential, suggesting that these conductances are present, but very small (< 20 pA) in Purkinje cells. Attempts to identify time- and voltage-dependent delayed rectifier K+ current(s) in Purkinje cells failed, although a slow delayed rectifier was observed in ventricular myocytes. 5. These results demonstrate significant differences in action potential waveform, and underlying K+ currents in rabbit Purkinje and ventricular myocytes. Purkinje cells express a much smaller IK1, and a larger It than ventricular myocytes. These differences in current densities can explain some of the most important electrophysiological properties of these two tissues.
authors.affiliation: Department of Physiology and Biophysics, University of Calgary School of Medicine, Calgary, Alberta, Canada.
authors.forename: J M
authors.initials: JM
authors.lastname: Cordeiro
authors.forename: K W
authors.initials: KW
authors.lastname: Spitzer
authors.forename: W R
authors.initials: WR
authors.lastname: Giles
mesh_terms: D015761:4-Aminopyridine / Q000494:pharmacology; D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D048429:Cell Size / Q000502:physiology; D051668:Delayed Rectifier Potassium Channels; D006352:Heart Ventricles / Q000737:chemistry / Q000166:cytology; D018485:Muscle Fibers, Skeletal / Q000737:chemistry / Q000502:physiology*; D009206:Myocardium / Q000737:chemistry / Q000166:cytology; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism* / Q000493:pharmacokinetics; D015221:Potassium Channels / Q000502:physiology; D024642:Potassium Channels, Voltage-Gated; D011690:Purkinje Fibers / Q000737:chemistry / Q000166:cytology / Q000502:physiology*; D011817:Rabbits
chemical_list: D051668:Delayed Rectifier Potassium Channels; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated; D015761:4-Aminopyridine; D011188:Potassium