Phosphorylation of myosin light-chain kinase (MLCK) hy protein kinase A (PKA) inhibits MLCK activation by Ca²⁺ calmodulin. Drugs such as albuterol bind to β-adrenergic receptor, which cause a rise in cAMP in cells and activation of PKA activity. Explain why albuterol is useful for treating the severe contraction of the smooth muscle cells surrounding airway passages involved in an asthma attack.