Electrical and pharmacological properties of mammalian neuroglial cells in tissue-culture

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Abstract
Neuroglial cells growing in short-term tissue-cultures of mammalian [rabbit] brain were impaled with microelectrodes under microscopic visual control. All the membrane potentials were internally negative with a mean value of -31 mV. They were reversibly depolarized by raising the external potassium ion concentration in the presence of low, normal and high chloride concentrations. No effect on glial membrane potentials was obtained by applying acetylcholine, adrenaline, noradrenaline, 5-hydroxytryptamine, sodium glutamate or barium ions. The "response" of these cells to extracellular stimulation through saline-filled glass micropipettes has been analysed. The mean amplitude is 8.0 mV and the mean half-time of repolarization 1.5 s. Typical stimulus parameters were a 3 ms cathodal current pulse of 40 [mu]A intensity, delivered through a pipette of 10 [mu]m tip diameter placed 10 [mu]m away from the cell membrane. These stimuli had a powerful mechanical component (due to electro-osmosis and electrophoresis) which could cause visible mechanical damage to the cells. The "response" could easily be obtained in HeLa cells and fibroblasts; it was not abolished by local anaesthetics or by sodium substitutes; and it could not be elicited by intracellular stimuli causing less than 200 mV displacement of membrane potential in either direction. The "response" could readily be produced by purely mechanical percussion of the cell membrane, or by displacement of the membrane potential to a level sufficient to cause demonstrable dielectric breakdown (above 250 mV in either direction). The "response" did not resemble regenerative responses in other excitable tissues, but did resemble closely the known effects of mechanical and of dielectric breakdown of cell membranes. The evidence showed that the "response" in tissue-cultured cells was due largely to mechanical breakdown of the cell membrane. Since the membrane behaves passively, the term "response" should be abandoned; the phenomenon is an artifact and has no neurophysiological significance. In the intact brain (where a similar "response" has been reported by other workers), the mechanical pulse would be absent, and it is suggested that there the effect might be due to dielectric breakdown. The input resistance of glial cells ranged from 0.5 to 10.5 M[OMEGA]O (mean = 4.2 M[OMEGA]). It was not feasible to estimate the specific membrane resistance.