Electrogenic sodium pump in rabbit atrio-ventricular node cell

AbstractElectrogenicity of the Na pump was demonstrated in rabbit A-V node cells by analysing the K-induced hyperpolarization occurring after a short period of K-free perfusion. The transient hyperpolarization was abolished completely by strophanthidin (10−5 M). The membrane slope conductance remained unchanged during the transient hyperpolarization. On perfusion of 50 mM K after K-free incubation the transient hyperpolarization reached −69 mV which was more negative than the expected EK (about −28 mV). The order of potencies of monovalent cations to activate the K site of the Na pump was Tl>Rb $$ \doteqdot$$ K>NH4 $$ \doteqdot$$ Cs>Li, which was similar to the sequence reported in the literature. Michaclis-Menten type activation of the K site of the Na pump was suggested from the relationship between the decay rate constant of the K-induced outward current transient and [K]0. These findings obviously indicate that the Na pump in the A-V node cells shares common characteristics with those of other excitable tissues. Direct contribution of the pump activity to the membrane potential under physiological conditions was suggested by a significant depolarization occurring immediately after application of strophanthidin.