Activation of beta-2 adrenergic receptors manifests with an increase in intracellular cAMP, a secondary messenger, that then activates protein kinase A. The function of protein kinase A is to phosphorylate MLCK and inactivate it. MLCK is an important mediator of the myosin-actin bridge formation and therefore, smooth muscle contraction. The overall effect is relaxation of smooth muscle including bronchodilation and peripheral vasodilation.
Protein kinase C, phosphoinositol, and calcium are not the secondary messengers involved in beta-2 agonist activity.
References:
Szymanski MW, Singh DP. Isoproterenol. [Updated 2020 May 5]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK526042/
