Ionic currents were recorded in cultured oligodendrocytes from the brain of trout using the whole-cell configuration of the patch-clamp technique. Outward currents were evoked at membrane potentials more positive than -40 mV, which could be separated into two components according to their kinetic parameters and their sensitivity to the holding potential: a fast inactivating current which was completely suppressed by 4-aminopyridine and reduced by tetraethylammonium and a slow steady-state conductance which was similarly sensitive to both potassium channel blockers. The current reversal potential was close to the potassium equilibrium potential. In contrast to mammalian oligodendrocytes but in similarity with cultured Schwann cells, trout oligodendrocytes did not exhibit any inwardly rectifying currents at hyperpolarized membrane potentials.
