Morphological changes do not reflect biochemical and functional differentiation in OLN-93 oligodendroglial cells

OLN-93 cells, a cell line established from spontaneously transformed rat brain glial cultures, are used as a model for oligodendrocytes. These cells are known to undergo morphological changes upon serum deprivation. The objective of the present study is to investigate a possible correlation between these morphological changes and (1) the loss or gain of oligodendrocyte markers and (2) the electrophysiological properties of these cells. Using RT-PCR and immunocytochemistry, we demonstrate that the OLN-93 cell line expresses a broad range of markers (NG2, CNP, MAG, MOG) both when cultured in medium containing 10% or 0.5% fetal calf serum. Whole-cell patch-clamp recordings demonstrate that, regardless of the culture conditions, OLN-93 cells mainly express delayed-rectifying K+ currents, a characteristic of immature oligodendrocytes. These currents are in part mediated by the shaker family of voltage-gated potassium channels. Kv1.1 and Kv1.3-expression are present at the mRNA and at the protein levels, and functional evidence for Kv1.3 mediated currents was obtained by using the selective blocker margatoxin. Under low serum conditions, OLN-93 cells exhibit differentiation-like morphological changes. However, we provide evidence that these morphological modifications do not necessarily correlate with biochemical or functional changes. Based on these data, we conclude that the OLN-93 cell line can be situated at a developmental stage between a late pre-oligodendrocyte and a late immature oligodendrocyte, regardless of serum concentration.