Carrier‐mediated Cl − transport in cultured mouse oligodendrocytes

We studied the steady state and the regulation of intracellular Cl − activity (aCl − i ) and the mechanisms of KCl uptake in cultured oligodendrocytes from mouse spinal cord using Cl − ‐selective microelectrodes. The majority of oligodendrocytes actively accumulated Cl − above passive distribution (2–3 mM), few cells showed a passive Cl − distribution. To identify the carriers mediating Cl − uptake, oligodendrocytes were maintained in a solution with low extracellular Cl − concentration ([Cl − ] 0 ) which resulted in a rapid decrease in aCl − i . The recovery of aCl − i above its passive distribution in normal [Cl − ] 0 was blocked in the absence of Na + or in the presence of furosemide and of bumetanide, which has been reported to inhibit Na + /K + /Cl − cotransport. We therefore conclude that Cl − uptake is primarily due to the activity of a Na + /K + /Cl − transport system. Cl − uptake above passive distribution was not affected in HCO 3 − ‐free solution or in the presence of SITS and DIDS, indicating that Cl − /HCO 3 − exchange is not involved in Cl − uptake by oligodendrocytes. Elevation of [K + ] 0 induced an increase in aCl − i and, as shown earlier, intracellular K + activity. This K + ‐induced Cl − uptake was not blocked by bumetanide, furosemide, SITS, or DIDS, suggesting that under conditions of raised [K + ] 0 the combined uptake of K + and Cl − is not mediated by a carrier, but can be explained by the entry through channels driven by Donnan forces.