Fig. 4.

β₂AR desensitization and intracellular signaling in isolated human ASM cells. A: cultured primary human ASM cells were incubated for 18 h with ascorbic acid (AA) or β-agonist (Iso), and cAMP was measured by CatchPoint assay (Molecular Devices). Iso-mediated accumulation of cAMP (15 min) is abrogated in human ASM cells that were pretreated for 18 h with β-agonist, but not in untreated cells (means ± SE, n = 4 experiments). NS, nonsignificant. *P < 0.01. B: human ASM cells were loaded with Fluo-4 AM, and intracellular Ca²⁺ concentration ([Ca²⁺]_i) release evoked by TAS2R activation was measured. Arrow indicates the time of Chloro addition. [Ca²⁺]_i transient curves to 1 mM Chloro is unabated in human ASM cells that were pretreated for 18 h with β-agonist. Results shown are from a single representative experiment of 3 performed.