Defective extracellular calcium (Ca-omicron)-sensing receptor (CaR)-mediated stimulation of a Ca2+-activated potassium channel in glioblastoma cells transfected with a dominant negative CaR

Glioblastoma cells exhibit several forms of sensitivity to extracellular ca lcium (Ca,) that might be conferred by the Ca-o-sensing receptor (CaR) that is intimately involved in the maintenance of Ca-o homeostasis by various c ell types. This receptor is expressed in human glioblastoma cell line, U87, and here we show that CaR activators stimulate a Ca2+-activated potassium (K+) channel (CAKC) with a conductance of 140 pS. The responses to CaR acti vators, however, were blunted in U87 cells transfected with a CaR bearing a n inactivating mutation (R185Q) that has previously been shown to exert a d ominant negative (DN) action on the wild type receptor. Raising Ca-o from 0 .75 to 2.0 mM or addition of a polycationic CaR agonist, each activated CAK C in nontransfected wild type and empty vector-transfected U87 cells, while they had little or no effect on channel activity in cells expressing the D N CaR (DN-CaR cells). In nontransfected wild type and empty vector-transfec ted cells, the specific `calcimimetic' CaR activator, NPS R-467, stimulated the channel, while its less active stereoisomer, NPS S-467, did not. In DN -CaR cells, in contrast, NPS R-467, had no effect on channel activity, sugg esting defective coupling of the CaR to this ion channel. CaR-mediated stim ulation of these K+ channels could lead to membrane repolarization and rela ted changes in cellular function under normal conditions. Since the R185Q m utation in the CaR produces a more severe phenotype in humans than most ina ctivating mutations of this receptor, some of its clinical consequences cou ld potentially result from abnormal CaR-dependent channel functioning. (C) 2000 Elsevier Science B.V. All rights reserved.