Electrophysiology and innervation of the smooth muscle of dog inferior vena cava.

1. Electrical properties of outer and inner muscles of three portions of dog inferior vena cava and their catecholaminergic innervation were investigated by microelectrode recording and an immunohistochemical technique. 2. There was no difference in the electrical properties of outer and inner muscles of the supradiaphragmatic (portion a) or the infrarenal (portion c) segments which had a quiescent membrane potential, delayed rectification, strong outward going rectification and no action potential. 3. In the longitudinal muscle which made up most of the segment (portion b) between the liver and renal veins, some of the outermost cells fired slow discharges and others action potentials in response to depolarizing current, but no cells from the innermost layer of longitudinal muscle of this portion did so. 4. All smooth muscle portions of the inferior vena cava showed a current spread in the direction of the long axis of the cell. Mean values of space constant of portions a, b and c were 2.25, 1.15 and 0.99 mm, respectively. 5. Noradrenergic nerve terminals were widely distributed in the longitudinal muscle layer of portion b and the circular muscle layer of portion c. Few nerve terminals were seen in any part of portion a. 6. The results suggest that a tendency to repetitive electrical activity was associated with outer smooth muscle aligned longitudinally, though a low space constant may have been associated with noradrenergic innervation.