The Spontaneous Action Potential of Rabbit Atrioventricular Node Cells

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Abstract
The rabbit atrioventricular (A-V) node (.apprx. 5 .times. 3 mm) was dissected into 15 small specimens (0.5 .times. 0.5 mm). A majority of the specimens continued to discharge spontaneous action potentials, the action potential configuration being almost identical in different specimens. The amplitude (98 mV) and the maximum rate of rise of the action potential (11 V/sec) were similar to those recorded from the intact A-V node (amplitude 98 mV, maximum rate of rise of action potential 12 V/s). In these small specimens the resting membrane potential (-44 mV) was .apprx. 20 mV less negative than that in the intact A-V node preparation (-62 mV) before the dissecting procedure. The spontaneous discharge in these small A-V node specimens was attributed to the low resting membrane potential. The small specimen became inexcitable under the effects of blockers of iS [slow inward current] though tetrodotoxin had no significant effect on the action potential. The afterhyperpolarization was observed after cessation of the depolarizing current pulse. The slow kinetics of the outward current contribute to the generation of the spontaneous A-V node action potentials as in the sinoatrial node.