GROWTH OF CHINESE-HAMSTER OVARY (CHO) CELLS EXPRESSING THE 5-HT2 SEROTONIN RECEPTOR IN SUSPENSION-CULTURE - AN EFFICIENT METHOD FOR LARGE-SCALE ACQUISITION OF MEMBRANE-PROTEIN FOR DRUG-EVALUATION

Chinese hamster ovary (CHO) cells expressing the rat 5-HT2 serotonin r eceptor were grown and evaluated in suspension culture to provide an e fficient method of producing membrane-bound receptors for drug discove ry. Expression of the 5-HT, receptor in cells grown in batch suspensio n culture fluctuated as a function of culture age. Both receptor expre ssion and receptor G-protein coupling were the highest early (1.9 pmol /mg membrane protein) but declined rapidly as the culture increased in age. However, addition of fresh serum-containing medium to stationary -phase cells reversed the decline and, after 24 h of growth, resulted in maximal receptor density and G-protein coupling. This serum respons e was found to be reproducible and lead to the establishment of a semi -continuous batch culture system in which cells were maintained in a g rowth state that supported high levels of membrane-incorporated and G protein-coupled receptors. In this system, 50% of the culture volume c ould be removed at 24-h intervals for membrane preparation and the los t volume replenished with fresh medium, resulting in a continuous supp ly of high-quality membrane preparations.