How does the formoterol component of Fostair 100/6 inhalation solution open the airways?

Formoterol in Fostair 100/6 inhalation solution selectively stimulates beta2-adrenergic receptors, relaxing bronchial smooth muscle in patients with reversible airways obstruction; its airway-opening effect begins within 1–3 minutes after inhalation and lasts 12 hours after a single dose.