title: Slow inward current and its role mediating the chronotropic effect of epinephrine in the rabbit sinoatrial node.
abstract: The ionic mechanism underlying the chronotropic effect of epinephrine on the rabbit sinoatrial (S-A) node has been studied. Epinephrine (5.5 X 10(-6) M) increased the spontaneous rate from 206 +/- 25 min-1 to 242 +/- 39 min-1. The effect of epinephrine was reproducible on repetitive applications. Voltage clamp experiments using the two microelectrode technique revealed the following changes in the membrane current: epinephrine (5.5 X 10(-7) M) increased the limiting conductance for the slow inward current (is) by approximately 30% and the potassium current (ik) by about 10%, keeping the kinetics of is and ik constant. From the holding potential of -70 mV the activation of is was observed on step depolarization positive to -60 or -55 mV in both control and epinephrine solution. The hyperpolarization-activated current (ih) was also increased by about 20% at -70 mV, and its time course was slightly accelerated. Participation of is for the chronotropic effect of epinephrine was strongly suggested by the findings that is was partially available positive to -60 mV and that epinephrine could not increase the slope of diastolic depolarization when is was blocked by D 600.
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D004837:Epinephrine / Q000494:pharmacology*; D006339:Heart Rate / Q000187:drug effects*; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D011817:Rabbits; D012849:Sinoatrial Node / Q000502:physiology*
chemical_list: D004837:Epinephrine