[Membrane current and Ca++-transport during the action potential of the rabbit atrium changed by acetylcholine and...

Using a modified sucrose gap technique action potential and phase plane trajectories of trabeculae from the left rabbit's auricle were recorded. By means of a numerical treatment and some mathematical model interpretations from these measurements current-voltage-(I-V)-relationships and the amount of inward transported calcium are calculated. A time independent K+-current shows that a voltage region within the anomalous rectification should exist. By acetylcholine the anomalous rectification is abolished and the inward transported amount of Ca-ions by the action potential (Q) decreases. A conductance of the K+-current gK will be dimished by decreasing the extracellular calcium concentration. The amount of inward transported calcium does not change significantly by variation of the extracellular calcium concentration. The calcium amount Q should contribute 17% of the calcium necessary for maximum contraction.