Fig. 7. Dual recording from a pair of circular muscle cells within 3 mm of the inner nerve ring. All muscle action potentials were spontaneous. The break in the traces represents a time break in the record. In the first segment, a single hyperpolarizing current (approximately 1 nA) was injected into the cell represented by the lower trace. The small hyperpolarization in the top trace (arrow) indicates the cells were electrically coupled. In the second segment, two current pulses were injected into the cell represented by the top trace. Again, small hyperpolarizations in the other cell (arrows) demonstrated similar coupling in the opposite direction.