text: The tertiary butyl group in salbutamol makes it more selective for β receptors, which are the predominant receptors on the bronchial smooth muscles. Activation of these receptors causes adenylyl cyclase to convert ATP to cAMP, beginning the signalling cascade that ends with the inhibition of myosin phosphorylation and lowering the intracellular concentration of calcium ions (myosin phosphorylation and calcium ions are necessary for muscle contractions). The increase in cAMP also inhibits inflammatory cells in the airway, such as basophils, eosinophils, and most especially mast cells, from releasing inflammatory mediators and cytokines. Salbutamol and other β receptor agonists also increase the conductance of channels sensitive to calcium and potassium ions, leading to hyperpolarization and relaxation of bronchial smooth muscles.
  Salbutamol is either filtered out by the kidneys directly or is first metabolized into the 4′-O-sulfate, which is excreted in the urine.