Pharmacodynamics and Receptor Theory

All of the following statements regarding G-protein coupled receptors (GPCRs) are correct EXCEPT:

All of the following are true regarding dose-response curves and pharmacodynamic principles EXCEPT:

A 52-year-old man with hypertension is started on atenolol 50 mg daily. After 2 weeks, his blood pressure remains 160/100 mmHg. On examination, heart rate is 58 bpm and regular. He reports no adverse effects. What is the most appropriate next step in management?

A 38-year-old woman with acute asthma exacerbation is treated with salbutamol nebulization. After 20 minutes, her peak expiratory flow improves from 180 L/min to 280 L/min, but she remains dyspneic with an oxygen saturation of 88% on room air. Respiratory rate is 26/min. What is the most appropriate next step in management?

A 38-year-old woman with asthma is prescribed albuterol (salbutamol) 2 puffs every 4–6 hours as needed. After 3 months of frequent use (8–10 puffs daily), she reports that each dose now provides only 2–3 hours of bronchodilation instead of the usual 4–6 hours, and her peak flow improvement is noticeably reduced. She denies any change in inhaler technique or adherence to other medications. Pulmonary function testing shows baseline FEV₁ has declined. Which receptor-level mechanism best explains her loss of bronchodilator efficacy?