Expression of an ouabain resistance gene in transfected cells. Ouabain treatment induces a K⁺-transport system

We have investigated the expression of a cloned mouse gene which confers ouabain resistance to African green monkey kidney (CV1) cells. CV1 cells carrying the transfected ouabain resistance (oua(R)) gene express an ouabain-inducible K⁺-transport system. This K⁺-transport system is not a normal (Na,K)-ATPase since plasma membranes prepared from the transfected cells have significantly reduced Na⁺-stimulated ATPase activity. RNA sequences homologous to the transfected gene are observed in abundance only following exposure of transfectants to ouabain. The small size of the message induced (1.2 kilobases) also argues that the gene does not code for the α-subunit of the (Na,K)-ATPase. Ouabain-treated transfected cells maintain an internal [K⁺] of 113 mM; a level close to the 139 mM of control cells. However, ouabain-treated transfectants exhibit an internal [Na⁺] of 61 mM, which is 3-6 times the level in untreated cells (11-21 mM). These results suggest: 1) ouabain resistance can be conferred by a gene which codes for an ouabain-inducible K⁺-transport system; 2) induction of this transport system by ouabain is due to increased levels of mRNA coded for by the ouabain resistance gene; and 3) the ouabain resistance gene does not encode for the α-subunit of the (Na,K)-ATPase.