A role for inwardly rectifying K+ channels in differentiation of NG108-15 neuroblastoma x glioma cells

The whole-cell patch-clamp technique was used to assess the current carried by inwardly rectifying K+ channels (K-ir) and the resting membrane potenti al (RMP) during long-term culture of NG108-15 cells. Culture of this cell l ine in serum-free medium triggers differentiation of a type I, neuron-like cell type followed hy an eventual predominance of a type III proliferative cell type, NG108-15 K-ir currents, which strongly resemble currents carried by human ether-ago-go related gene (HERG) K+ channels, exhibited significa ntly smaller current density for the more depolarized undifferentiated cell s in growth media (GM) and type II cells compared to the neuron-like type I cells. Detailed examination of the transition from undifferentiated GM cel ls to type I cells revealed a shift in the voltage dependence of K-ir activ ation which paralleled the more hyperpolarized RMP, neurite outgrowth, and biochemical differentiation characteristic of type I cells. Reverse-transcr iption polymerase chain reaction experiments using primers for the rat vari ant of HERG, RERG, revealed a a nearly twofold increase in RERG mRNA as cel ls differentiate from GM to type I, a finding entirely consistent with the increased K-ir current density derived from patch-clamp recordings, Adminis tration of CsCl (5 mM) blocked K-ir currents and depolarized the RMP of typ e I cells. Furthermore, culture of NG108-15 cells in serum-free medium but with CsCl added significantly prevented neurite extension, an effect which was entirely reversible upon subsequent removal of CsCl, In contrast, other K+ channel inhibitors (4-aminopyridine and tetraethylammonium), at concent rations without marked effects on K-ir, failed to affect neurite extension. These results suggest an important role of the K-ir channels in determinin g the RMP and triggering morphological differentiation of the cell line. (C ) 1999 John Wiley & Sons, Inc.