Weak electrotonic interaction between neighboring visceral smooth muscle cells

The electrotonic spread of current was determined by double microelectrodes cemented at various distances. A bridge circuit enabled transmembrane potentials to be recorded at zero distance from injected current. At interelectrode distances of 100 µ or greater, with the electrodes oriented parallel to the cell axes, current flow of 20 x 10 –9 amp through one intracellular electrode produced almost no change in potential at the second electrode. At interelectrode distances of 40 µ or less, similar currents through a given electrode pair produced either a substantial or a small change in potential depending on the impalement. With transverse electrode orientation, no substantial interactions occurred at distances of 17 µ or greater. Various criteria, including the congruous decline in resting potential on both channels, indicated when both electrodes impaled the same cell. The degree of electrotonic spread did not depend on the interelectrode distance per se at close distances. Thus, current flow through one cell does not have substantial effect on the transmembrane potentials of adjacent cells.