Characterization of the Na/K pump current in N20.1 oligodendrocytes

Glial cell Na,K-ATPase is suggested to participate in extracellular K+ concentration ([K+](o)) control by being activated when [K+](o) rises in the brain. The extent of that activation directly depends on the Na/K pump affinity to [K+](o), intracellular Na+ ([Na+](i)) and, indirectly on pump cycle regulation by membrane potential (V-m). In the present investigation, these Na/K pump properties were studied with the whole-cell patch-clamp technique in cultured mouse oligodendrocytes (N20.1 cell line). N20.1 cells possess ouabain-sensitive Na/K pump current (I-p) with a maximal density of 0.5-0.6 pA/pF (estimated for conditions of Na/K pump stimulation by saturating [Na+](i), [ATP](i), [K+](o) and at positive V-m). This current was half-inhibited at 83 +/- 31 mu M ouabain, and half-activated by [Na+](i) of 9.6 +/- 1.1 mM, by [K+](o) of 2.0 +/- 0.1 mM and by membrane potential at about -65 mV. High levels of nervous activity may increase [K+](o) from 3 to 12 mM which would only increase Na/K pump current by 40% due to the direct effect of [K+](o). However, elevated [K+](o) would also depolarize the glial cell membrane which would indirectly activate I-p and together with the direct effect of [K+](o) would increase I-p as much as 2-2.5-fold. These data suggest that glial cell Na/K pump regulation by V-m may be an important factor in determining the participation of the Na/K pump in [K+](o) homeostasis in the nervous system.