Swelling-induced changes in electrophysiological properties of cultured astrocytes and oligodendrocytes. II. Whole-cell currents

Abstract

Using whole cell patch-clamp recordings we have found that swelling cultured cerebrocortial astrocytes or mouse spinal cord oligodendrocytes by perfusing them with hypotonic medium induced inward currents at the normal resting potential of −60 mV. The currents in the oligodendrocytes were always less than for astrocytes. We examined the reversal potentials of these responses by rapidly jumping the holding potential to different values and measuring the currents. We found that the hypotonic medium-induced conductance increase was always preceded by a conductance decrease in the case of oligodendrocytes, but only sometimes preceded by a conductance decrease in cultured astrocytes. The reversal potential of the conductance increase for astrocytes was around −40 mV, while the conductance decrease had a more negative reversal potential of −60 mV or less. For oligodendrocytes the reversal potential for the conductance increase was around −50 mV while the conductance decrease had a reversal potential of −90 mV or less. This suggests that K + conductance decreased in the initial phase, while the conductance increase was due to additional channel openings. Ion substitution experiments in the case of the astrocytes showed that the reversal potential was shifted to a more positive value when medium K + was increased, but was unaffected when Na + was substituted by N-methyl- d-glucamine or Cl − by d-glucuronate, when corrected for liquid junction potential changes. Thus, the channels opened in these cells are likely to include non-specific cation channels. It is of interest that the two cells show a difference in their responses, and in the case of astrocytes these are likely to be involved in the regulatory volume decrease processes documented in these cells.