Ion Transport in Glial and Neuroblastoma Cells

Abstract: The aim of this thesis has been to increase our understanding of the ion channel function and the ion transport mechanisms in glial cells. The analysis has also covered Na channel function in human neuroblastoma cells in order to get a basis for similar studies of glial cells In paper I isotopes 42K and 201 Tl were used to compare the K+ transport properties in cell lines from human malignant gliomas (U-251MG and Tp-378MG), carcinomas, and brain metastasis. In papers II and Ill the patch-clamp technique has been used in studies of the membrane potential and K+ conductance in human glioma cells (U-251MG) and in astrocytes of primary cultures from newborn rats. Paper IV is a patch clamp analysis of the Na+ channel voltage dependence in a human neuroblastoma (SK-N-SH) and esthcsioneuroblastoma (Tp-410) cell line.From these studies it was concluded that:(1) Cultured human glioma cells have a high specific K+ and Tl+ uptake of which approximately 90% is carried by Na,K-ATPase-dependent transport and Na-K-Cl cotransport. Inwardly rectifying K+ channels seem to have little importance for the K+ -uptake, at least in isolated cells.(2) The membrane potential in rat astrocytes hyperpolarizes while human glioma cells depolarize in low concentrations of K+. This difference may be related to the effect of K+ on inwardly rectifying K+ channels which were present in higher density in human glioma cells.(3) ca2+ free solutions depolarize the cells which seem to involve a transformation of K+ channels to unspecific leakage channels in rat astrocytes. The depolarization caused by Ba2+ was explained by a block of K+ channels.(4) Metabolic inhibition with protonophores (DNP and FCCP) is associated with specific effects on the plasmalemma in rat astrocytes in addition to the inhibition of the cellular ATP production. These agents should therefore be used with caution in studies of energy dependent mechanisms at the cellular level.(6) Neuroblastoma SK-N-SH cells and esthesioneuroblastoma Tp-410 cells have prominent Na+ currents. Both activation .and inactivation of the Na+ channels differed in their time and voltage dependence between these two types of neuroblastoma ce11s.