Intracellular pH shifts capable of uncoupling cultured oligodendrocytes are seen only in low HCO 3 − solution

Electrical coupling between cultured mouse oligodendrocytes was transiently blocked when pH i was decreased below about 6.5 using the NH 4 + prepulse method. This uncoupling could, however, only be achieved if the dominant pH i regulating mechanism in these cells, the Na + /HCO 3 − cotransporter, was blocked by lowering bath [HCO 3 − ]. Under this condition, an NH 4 + prepulse caused pH i to decrease toward the passive distribution for H + (i.e., about pH 6.2). In the presence of normal bath [HCO 3 − ] an NH 4 + prepulse did not decrease pH i below 6.5 even when the second pH i regulating mechanism, the Na + /H + exchanger, was blocked by amiloride, and consequently oligodendrocytes could not be uncoupled. Increasing CO 2 , which uncouples glial cells in situ (Connors et al: J. Neurosci. 4:1324–1330, 1984), did not uncouple cultured oligodendrocytes in the presence of normal bath [HCO 3 − ], but did cause uncoupling in low [HCO 3 − ] solution. These results indicate that electrical coupling between cultured oligodendrocytes is sensitive to pH i ; in normal bath [HCO 3 − ], however, the pH i regulation of these cells is so effective that standard techniques for intracellular accidification are unable to lower pH i to levels which cause the closure of oligodendrocyte gap junctions.