ALPHA(2A) ADRENERGIC-RECEPTORS INHIBIT CAMP ACCUMULATION IN EMBRYONICSTEM-CELLS WHICH LACK G(I-ALPHA-2)

alpha(2A) adrenergic receptors are thought to inhibit adenylyl cyclase primarily through G(i alpha 2). We tested the requirement for G(i alp ha 2) to inhibit cAMP accumulation by stable expression of alpha(2A) a drenergic receptors in mouse embryonic stem cells. Host lines consiste d of wild-type CCE cells, and CCE cells with targeted disruption of th e G(i alpha 2) gene by two-stage homologous recombination (Mortensen, R. M., Zubiuar, M., Neer, E. J., and Seidman, J. G. (1991) Proc. Natl. Acad. Sci. U. S. A. 88, 7036-7040; Mortensen, R. M., Conner, D. A., C hao, S., Geisterfer-Lowrance, A. A., and Seidman, J. G. (1992) Mol. Ce ll. Biol. 12, 2391-2395). Knockouts were confirmed by Northern blot an d immunoblot. We studied three clones derived from wild-type CCE cells (2, 6, and 8) expressing 450 +/- 50, 3000 +/- 120, and 150 +/- 20 fmo l of receptor/mg of protein, respectively, and two G(i alpha 2)-null c lones (7 and 18) expressing 2100 +/- 250 and 300 +/- 40 fmol of recept or/mg of protein. The specific agonist UK14304 caused an inhibition of cAMP accumulation in clones 2,6 and 8 (58 +/- 16%, 62 +/- 7%, and 52 +/- 12%) and in clones 7 (47 +/- 3%) and 18 (40 +/- 5%), but not in no ntransfected CCE cells. IC50 values were similar for all clones (appro ximate to 200 nM). The effect was attenuated by pertussis toxin and th e antagonist rauwolscine. These studies show that expression of G(i al pha 2) is not required for alpha(2A) adrenergic receptors to inhibit c AMP accumulation.