GPCR priming not affected by β2-AR tail deletion and filipin treatment. (A) Deletion of β2-AR tail domain (amino acids 351–413) after helix H8 results in truncated β2-AR (tβ2-AR). tβ2-AR sensors tethered to Gαs, Gαq, or a control peptide (−) were expressed in cells to equivalent levels. Increase in cAMP levels measured between isoproterenol (10 μM) and buffer-treated HEK293T cells expressing equivalent amount of tβ2-AR sensors. Progressive increase in cAMP levels is noted for expression of tβ2-AR (−), tβ2-AR–s-pep, and tβ2-AR–q-pep. (B) Effect of filipin on cAMP response. HEK293T cells expressing equivalent levels of β2-AR–Gαs or β2-AR–Gαq sensor were treated with filipin (2 μg/mL, 15 min) or buffer. Increase in cAMP was measured for these cells upon exposure to isoproterenol (10 μM), compared with buffer treatment. In filipin-treated cells, β2-AR–Gαq sensor has an increased cAMP response than β2-AR–Gαs sensor, similar to control pair. Results are expressed as mean ± SEM. (A) Two independent experiments, n > 8 observations; (B) five independent experiments, n >15 observations. **P < 0.01, ***P < 0.005 by unpaired t test.