Brain Research, 480 (1989) 249- 258 249 Elsevier BRE 14263 Inward rectifying potassium channels in human malignant glioma cells T. Brismar and V.P. Collins Departme~.tof ClinicalNeurophysiology and the Ludwig Institute for CancerResearch, Karolinska Hospital, Stockholm (Sweden) (Accepted 2 August 1988) Key words: Potassium channel; Inward rectification; Glial cell; Malignant glioma; Potassium homeostasis; Human Human glioma cells obtained from established cell lines (Tp-276MG. Tp-301MG, Tp-378MG, Tp-483MG and U-2.51MG)were analyzed for the presence of ion channels with the tight-seal voltage clamp technique. The current-voltage relation revealed a marked inward rectification at hyperpolarizingvoltages, due to the presence of inward rectifyingK-channelsin cells from all studied cell lines. These channels were conducting when the membrane potential was more negative than the K-equilibriumpotential. The slope con- ductance for the inward K-currents (g~) was affected both by [K÷], and [K+Io.g,~ was proportional to [K~]oraised to 0.35 or 0.50, of which the larger value was measured in the presence of low [K']i (25 raM). The rectificationwas not significantly different in cells per- fused with Mg-free EDTA-buffered internal solution. TI+ was 3.5 times more permeant than K÷. gr, was blocked by Cs÷ (1 raM) in a voltage-dependent way (more effective in the hyperpolarized membrane), and by Na÷ (154 mM) depending on voltage and time. From measurements of unitary current events in membrane patches (outside out or cell attached) the conductance of the singleinward rectifyingchannel was estimated to be 27 _+7 pS. This type of ion channel may be important for K-uptake by glial cells and hence for the K-bomeostasisin the brain. INTRODUCTION Several studies have indicated that glial cells are involved in the K-homeostasis in the brain. Glial cells have a membrane potential of about -90 mV, which is dependent on extraceilular [K+J27'47. Impulse ac- tivity in amphibian optic nerve fibres causes a few millivolt depolarization of the glial cells27, and simi- larly, in the cat visual cortex, glial cells respond with small graded depolarizations when the neighbouring neurons are excited by specific visual stimulation 24. Repolarization of neurons through an outflow of K + into the extraceUular clefts normally raises [K +] only 0.1-0.4 mM above its resting level of 3.0 mM. Much higher K-concentrations have been measured in pa- thological conditions such as anoxia, epileptic sei- zures and spreading depression 42. A pronounced and rapid uptake of 42K was found in cultured rat astro- cytes exposed to elevated [K+]~. The ionic permeability of ghal cells has recentl) been studied with the tight-seal voltage clamp tech- nique. In retinal MOiler cells of amphibia there are different types of K-currents, one of which is 'inward rectifying' operating at normal resting potentiaP ~2. Astrocytes from newborn rats exhibit several types of ion currents, viz. small neuronal type inward Na- currents, delayed outward K-currents, and Cl-cur- rents 2'3'35, Ca- and Ca-activated K-currents 3°'~, all of which are turned on at larger depolarizations than encountered in glial cells. There are also transmitter (y-aminobutyric acid, glutamate and aspartate) acti- vated channels in rat astrocytes and oligodendro- c.ytes ~,26. The present study was undertaken to elucidate the membrane ion channels of human glioma cells, espe- cially with regard to the mechanism that can he re- sponsible for K-uptake. We found that human malig- nant glioma cells had a high density of inward rectify- ing K-channels capable of large inward K-currenB at normal membrane potentials. The presence of out- Corrmpondence: T. Brismar, Department of Oinical Neurophysiol~D,,Karoliaska Sjuklmsct, S-I040I Stockholm, Swede. 0006-8993/89/$03.50~) 1989Elsevier Science Publishers B.V. (Bion~edi¢~Division)