title: Properties of the current if in the sino-atrial node of the rabbit compared with those of the current iK, in Purkinje fibres.
abstract: 1. Properties of the 'pace-maker' current if in rabbit sino-atrial node have been investigated by voltage clamp of small preparations and compared with those of the iK2 current in the Purkinje fibre. Besides having a similar voltage range of activation and responding in a similar way to adrenaline, if resembles iK2 in other respects. 2. When external Na is reduced, if decreases proportionally. In 25% Na the time-dependent current change due to if disappears. 3. 20 mM-Cs completely abolishes it. 4. The time constant of if during a hyperpolarizing voltage-clamp pulse displays a relatively high temperature dependence. 5. In spite of the similarities between the two current systems, experiments in high K solutions (48 mM) rule out the possibility that the current change seen on a hyperpolarization reflects the decay of a pure K current. 6. From conductance measurements during onset of if it is deduced that if behaves as an inward current activated by hyperpolarizations.
mesh_terms: D000818:Animals; D002586:Cesium / Q000494:pharmacology; D004553:Electric Conductivity; D006329:Heart Conduction System / Q000502:physiology*; D066298:In Vitro Techniques; D007473:Ion Channels / Q000187:drug effects; D007700:Kinetics; D008564:Membrane Potentials; D011188:Potassium / Q000494:pharmacology; D011690:Purkinje Fibers / Q000502:physiology*; D011817:Rabbits; D012849:Sinoatrial Node / Q000502:physiology*; D012964:Sodium / Q000494:pharmacology; D013696:Temperature
chemical_list: D007473:Ion Channels; D002586:Cesium; D012964:Sodium; D011188:Potassium