Electrical activity of single muscle cells of pregnant uteri studied with intracellular ultra-microelectrodes.

T HE succ.~ss of the Ling-Gerard intracellular ultramicroelectrode technique (I) in measuring inside-outside potentials of striated muscle, cardiac muscle, nerve, spinal cord and cerebral cortex suggests that this technique should be used to study single smooth muscle cells. External electrode studies have shed considerable light on the events occurring in the individual cells of nerve and striated muscle because of their simple parallel arrangement. Visceral smooth muscle, like cardiac muscle, forms syncytia composed of closely applied, differently oriented sheets of parallel cells. This complicated organization makes uncertain the interpretation of external electrical measurements. For example, Bozler (2-4), using closely spaced (differential) electrodes, contributed a great deal to the description and interpretation of smooth muscle electrical activity, but the complex action potentials he sometimes recorded could only be interpreted as the asynchronous discharge of many cells. However, some of these complex potentials are probably single unit action potentials like those reported by Greven (5) and in this paper. Intracellular electrodes thus seem to be the most direct and unequivocal way of studying electrical activity in smooth muscle. Two difficulties are encountered in attempting to record intracellularly from smooth muscle cells: a) Because these cells are comparatively small, membrane damage resulting from electrode insertion may reduce the potential significantly; and b) an actively contracting tissue is difficult to immobilize sufficiently to achieve and maintain electrode