ENDOGENOUS SUBUNITS CAN CAUSE AMBIGUITIES IN THE PHARMACOLOGY OF EXOGENOUS GAMMA-AMINOBUTYRIC ACID(A) RECEPTORS EXPRESSED IN HUMAN EMBRYONIC KIDNEY-293 CELLS

The physiological and pharmacological properties of GABA(A) receptors have been studied extensively after the expression of subunits in non- neural cells. Many of these studies have used the human embryonic kidn ey cell line HEK 293. We examined the properties of subunits that resu lt in the expression of low levels of functional receptors and found t hat the properties of the gamma-aminobutyric acid (GABA)-elicited resp onses in transfected HEK 293 cells differ from expectations based on p revious work and are consistent with the idea that the expressed recep tors do not necessarily contain the expected subunits. In particular, expression of a mutated beta 2 subunit [beta 2(Y205S)] in combination with alpha 1 and gamma 2L results in cells that have large responses t o pentobarbital (as expected) but also show appreciable responses to G ABA (contrary to expectation). Furthermore, transfection of HEK 293 ce lls with alpha 1 plus gamma 2L subunits results in responses to GABA t hat are potentiated by the drug loreclezole, suggesting that a subunit resembling the beta 2 or beta 3 subunit had assembled with the alpha 1 gamma 2L subunits. In addition, some nontransfected HEK 293 cells re spond to applications of GABA(A) and transfection of cells with alpha 1, beta 1, or gamma 2L subunits alone can result in the expression of GABA-elicited currents. In comparison, when QT6 quail fibroblasts are used as the expression system, no responses were seen in untransfected cells or in cells transfected with alpha 1, beta 1, or gamma 2L subun its alone or alpha 1 gamma 2L subunits. Furthermore, no response to GA BA was seen in QT6 cells transfected with alpha 1 beta 2(Y205S)gamma 2 L subunits, although cells gave strong responses to pentobarbital. The se observations indicate that caution must be taken in interpreting th e results of studies of the properties of GABA(A) receptors expressed in HEK 293 cells if the exogenous subunits result in the expression of low levels of functional GABA(A) receptors.