Intracellular Na+ activity in cultured mouse oligodendrocytes

Abstract

Na⁺-selective double-barrelled microelectrodes were used to measure the intracellular Na⁺ activity (aⁱ_Na) and membrane potential (E_m) in oligodendrocytes from cultures of embryonic mouse spinal cord. In Na⁺-free solutions aⁱ_Na rapidly fell from its baseline of about 15 mM to values below 1 mM. Elevation of the K⁺ concentration in the bath ([K⁺]_o) from 5.4 to 15 or 50 mM elicited an aⁱ_Na decrease of 4.7 or 9.0 mM, respectively. Ouabain blocked the aⁱ_Na decrease in response to 50 mM K⁺ by 37%. Bath application of 1 mM glutamate resulted in a membrane depolarization of 4.5 mV and a concomitant rise of aⁱ_Na by 8.6 mM. aⁱ_Na increased by approximately 11 mM after washout of a solution containing 20 mM NH₄⁺. This aⁱ_Na increase was not blocked by amiloride, excluding a major contribution of a Na⁺/H⁺ antiporter. We conclude that, in cultured oligodendrocytes, transmembraneous Na⁺ movements are involved in pH regulation, glutamate causes an influx of Na⁺, and that the Na⁺/K⁺ pump and passive KCI uptake contribute to K⁺ accumulation.