Swelling-induced changes in electrophysiological properties of cultured astrocytes and oligodendrocytes. I. Effects on membrane potentials, input impedance and cell-cell coupling.

We have studied the membrane potential responses of cultured oligodendrocytes and astrocytes during changes in the osmolarity of the bathing solution. Oligodendrocytes responded with a de- or hyperpolarization when changing to hypo- or hyperosmolar medium, consistent with dilution or concentration of intracellular [K+], respectively. Astrocytes responded with a similar hyperpolarization in hyperosmolar medium that could also be explained by an increase in intracellular [K+]. In hypoosmolar medium, however, a much larger depolarization of astrocytes was observed. These data imply that in astrocytes, in contrast to oligodendrocytes, swelling activates specific channels, which might be involved in volume control. Dual-impalement studies in single cells were used to measure effects of medium hypotonicity on cell input resistance, while dual-impalement studies on neighboring cells were used to measure changes in cell-cell coupling. In oligodendrocytes an increase in apparent cell input resistance and electrical coupling was found. In cultured astrocytes there was no change in apparent cell input resistance but an apparent decrease in cell-cell electrical coupling when cultures were exposed to the lowest medium osmolarity examined (-100 mM NaCl). However, because of the unavoidable contribution of cell-cell electrical coupling to the measurement of membrane impedance by current injection into a single cell a lack of change in apparent cell resistance could be due to offsetting changes in cell-cell coupling.