Nervous function at the cellular level: glia.

Abstract

Previous studies on the physiological properties of glial cells in the cen­ tral nervous system of the leech and amphibia were extended to mammals (3). Negative potential shifts, not associated with impulse activity, were recorded with micro electrodes from the rat optic nerve, and identified as the membrane potential of glial cells by means of iontophoretic injections of Procion yellow followed by histological examination; no distinction was made between astroglia and oligodendroglia. The membrane potential of these glial cells (77-85 mV) was higher than the values reported for mammalian neurons, and it appeared to depend mainly on the transmem­ brane gradient of potassium ions. Glial cells in the rat optic nerve, however, did not behave as ideal potassium electrodes-although some other glial cells nearly do (1 )-but Dennis & Gerschenfeld suggested that this finding may have been the result of cell injury during impalement. A similar devia­ tion from ideal potassium electrode behavior has been reported for Schwann cells surrounding squid giant nerve fibers (4). In this instance, the deviation was interpreted as due to a nonelectrolleutral inward transport of K+ because the membrane potential (40 m V) was relatively insensitive to changes in the external concentrations of Na+ and Cl-, and addition of a cardiac glycoside to the bathing fluid caused an immediate hyperpolarization of the Schwann cells, without significant changes in their ionic concentra­ tions.