Directional propagation of action potential within a single cell and intercellular conduction within a cell aggregate...

The mechanism of directional propagation of action potential throughout a single cell was examined using a liquid-membrane model cell system. In the experiments on the liquid-membrane model cell system, liquid-membrane cells were constructed to mimic the function of K⁺ and voltage-gated Na⁺ channels, which play important roles in action potential propagation. These channel-mimicking cells were connected electrically, and a model cell system was composed of four parts within the one cell. When one voltage-gated Na⁺ channel-mimicking cell was connected to form the action potential and generated the inflow current at the one part, action potential occurred in the surrounding area due to the local circulating current and propagated to the other parts. The action potential propagation throughout the cell by a brief electrical stimulus (10 ms) was easier than that by a long electrical stimulus (2 s). The long electric stimulus thus caused hyperpolarized region within the cell. Moreover, the increase in resistance corresponding to the extracellular fluid weakened the action potential propagation. In the simulation experiments using the software LTspice, the characteristics of K⁺ and Na⁺ channel-mimicking cells were reproduced in the electrical circuit also. A model cell aggregate consisting of closely packed three model cells and the extracellular fluid was constructed in the electric circuit. When one cell fired, the electrical signal propagated to the neighboring cells through the intercellular and extracellular fluids. This result suggests that electrical propagation can occur between independent cells in closely packed tissues without chemical transmission or direct propagation across the gap junctions.