title: Evidence for two types of calcium currents in frog cardiac sinus venosus cells.
abstract: Two types of calcium currents were recorded in single sinus venosus cells of the frog heart, using the whole-cell patch-clamp technique. The threshold potentials were approximately -65 mV for T-type current and -40 mV for L-type current. The amplitude and time course of T-type current were unaffected by exchanging calcium for barium, while the amplitude of L-type current was increased and its decay slowed. T-type current was neither modified by 10(-6) M nifedipine nor by 10(-7) M isoprenaline in contrast with the effects of these agents on L-type current. T-type current began to inactivate at -90 mV and was fully inactivated at -45 mV. Its steady-state inactivation curve was approximately 35 mV negative to that of L-type current. Overlap of activation and inactivation relationships was present for both T- and L-type currents and was maximal at -57 and -30 mV, respectively. It was concluded that T- and L-type currents can easily be separated by their voltage, kinetic and pharmacological differences. The presence of a high density of T-type current may be correlated to its contribution to the pacemaking function of the sinus venosus cells.
authors.affiliation: Laboratoire de Physiologie Générale, URA CNRS no. 290, Faculté des Sciences, Université de Poitiers, France.
authors.forename: P
authors.initials: P
authors.lastname: Bois
authors.forename: J
authors.initials: J
authors.lastname: Lenfant
mesh_terms: D000818:Animals; D001464:Barium / Q000493:pharmacokinetics / Q000502:physiology; D001683:Biological Clocks / Q000187:drug effects; D001692:Biological Transport / Q000187:drug effects; D002118:Calcium / Q000493:pharmacokinetics* / Q000502:physiology; D002462:Cell Membrane / Q000187:drug effects; D002463:Cell Membrane Permeability / Q000187:drug effects; D002469:Cell Separation / Q000379:methods; D004305:Dose-Response Relationship, Drug; D004553:Electric Conductivity / Q000187:drug effects; D006352:Heart Ventricles / Q000166:cytology*; D007545:Isoproterenol / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects; D009543:Nifedipine / Q000494:pharmacology; D011893:Rana esculenta / Q000502:physiology*; D016276:Ventricular Function
chemical_list: D001464:Barium; D009543:Nifedipine; D007545:Isoproterenol; D002118:Calcium