Membrane Currents in the Atrioventricular Node of the Rabbit

Abstract

The rabbit AV node was isolated and dissected into small strips of 0.3 mm width to apply two microelectrode voltage clamp technique. Then, slow inward current (isJ, hyperpolarization activated inward current (if) and pump current were recorded and their kinetic properties were analysed. The results obtained were as follows: 1. The isolated AV node continued to beat, but the rate was slower than that in the SA node. The configuration of action potential showed regional difference. Small AV node preparations also showed spontaneous action potentials whose configurations were similar to those in the SA node. Resting membrane potential was about -40 mV. 2. On depolarization from the holding potential of -40 mV to various potential level, slow inward current (isf) was recorded. It was disappeared by adding 2 mM Mn+ + and increased remarkably by 10-6M adrenaline. Current-voltage relationship, steady-state inactivation and recovery from inactivation were also studied and considered similar to those in other cardiac tissues. 3. In response to hyperpolarizing voltage clamp pulse, the current if was activated. The reversal potential was about -25 mV. 0.5 mM Cs" decreased if in a voltage-dependent manner. 10-6M adrenaline showed little effect on if. 4. The activity of electrogenic Na+ pump was demonstrated by K+ -induced transient outward current or transient hyperpolarization after pre-treatment with K+-free Tyrode solution. The pump activity was affected by duration of pre-treatment, K+ concentration in recovery solution and Ca + + concentration in K+ -free Tyrode solution.