Characterization of specific binding sites for [3H]-1,3-di-o-tolyl-guanidine (DTG) in the rat glioma cell line C6-BU-1.

The aim of the present study was to find out if a cell line of glial origin possesses sigma and/or phencyclidine (PCP) binding sites. Binding of [3H]1,3-di-o-tolyl-guanidine (DTG), a highly selective ligand for sigma binding sites, and of [3H]N-[1-(2-thienyl)cyclohexyl] piperidine ([3H]TCP), a radioligand specific for PCP receptors, to C6-BU-1 glioma cells was investigated. Binding of [3H]DTG to C6-BU-1 cell membranes was reversible, saturable (Bmax = 10.5 pmol/mg protein), and of high affinity (KD = 26 nM). C6-BU-1 cells do not possess PCP receptors as indicated by negligible specific binding of [3H]TCP to C6-BU-1 cell membranes. Specific binding of [3H]DTG was reduced in the presence of Ca2+ and to a lesser extent by Mg2+. The rank order of potency of various PCP and sigma ligands was DTG > (+)3-[(3-hydroxy-phenyl)-N-n-propyl-piperidine] [(+)3-PPP] > haloperidol > pentazocine > (-)3-PPP > PCP > metaphit > dextromethorphan > (-)butaclamol > (+)butaclamol > (-)N-allylnormetazocine [(-)SKF 10,047] > MK801 > (+)SKF 10,047 > ketamine. The drug specificity, confirmed by a reversed stereoselectivity for the benzomorphan opiate SKF 10,047, indicated that these sites correspond to a subtype of sigma binding sites, the so-called sigma 2 binding site. Thus, the C6-BU-1 cell line is the first glial cell line demonstrated to have sigma 2 binding sites.