NBEO General Physiology Practice Exam 2025 – Complete Study Resource

The correct answer involves receptors that activate the adenylate cyclase enzyme, leading to an increase in cyclic adenosine monophosphate (cAMP) levels within the cell. Beta 1 and Beta 2 adrenergic receptors are both coupled to Gs proteins. When activated by their corresponding neurotransmitters (like norepinephrine), these receptors stimulate adenylate cyclase, resulting in the conversion of ATP to cAMP. This increase in cAMP levels subsequently leads to various physiological effects, including enhanced cardiac contractility and smooth muscle relaxation.

In contrast, alpha 1 receptors are associated with the Gq protein, which primarily stimulates phospholipase C and leads to an increase in intracellular calcium rather than cAMP. Alpha 2 receptors, on the other hand, are coupled to Gi proteins and inhibit adenylate cyclase activity, resulting in decreased cAMP levels. Therefore, Beta 1 and Beta 2 are the only receptors in this context that effectively increase cAMP levels.