CHANGES IN ION-CHANNEL EXPRESSION DURING IN-VITRO DIFFERENTIATION OF TROUT OLIGODENDROCYTE PRECURSOR CELLS

Voltage-gated ionic currents were studied in cultured trout oligodendr ocyte precursor cells derived from larval trout brain with the whole-c ell mode of the patch-clamp technique. These bipolar cells which carry the ganglioside epitope A2B5 on their surface differentiated in vitro into immature multipolar oligodendrocytes expressing the myelin glyco protein IP2, which signifies the initial step of oligodendroglial deve lopment in fish CNS. Depolarization above -40 mV activated a fast tran sient sodium inward current that was eliminated by substituting Na+ fo r choline and blocked in the presence of 1 mu M TTX. The kinetics and the voltage-dependence of inactivation (half-maximal inactivation at - 68 mV) resembled those of sodium currents described in mammalian oligo dendrocyte precursor cells and CNS neurons. The expression of Na+ chan nels was developmentally regulated, since high amplitudes were measure d only in A2B5(+) cells with a characteristic bipolar morphology of gl ial progenitors. Depolarizing voltage steps, additionally elicited out ward potassium currents that were sensitive to external 4-AP. In a sub population of cells this outward current consisted of a sustained and a transient component. The amplitude of both components were dependent on the prepulse potential. (C) 1995 Wiley-Liss, Inc.