Figure 2.

Effects of isoproterenol and somatostatin on cAMP accumulation in transfected 293 cells. (A) Cells were treated for 15 min with varying concentrations of isoproterenol, and the intracellular cAMP concentration was determined. Accumulation of cAMP in response to isoproterenol did not differ significantly between control cells (Vector) and those expressing NH₆GAIP or MycRGS4. (B) Cells were treated with 5 μM isoproterenol (Iso) with or without 1 μM somatostatin (Stt) for 15 min. Somatostatin inhibits isoproterenol-stimulated cAMP accumulation in the control cells but is ineffective in cells expressing RGS4 or GAIP. The data points represent the mean, and the error bars represent the range of duplicate samples. Three independent experiments yielded similar results. Two independent clones of cells expressing NH₆GAIP or MycRGS4 gave qualitatively similar results.