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-]o) which resulted in a rapid decrease in aCl-i. The recovery of aCl-i above its passive distribution in normal [Cl-]o 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 HCO3(-)-free solution or in the presence of SITS and DIDS, indicating that Cl-/HCO3- exchange is not involved in Cl- uptake by oligodendrocytes. Elevation of [K+]o 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+]o 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.