Question

Cyclic AMP (cAMP) is a common relay molecule in many signal transduction pathways, including the beta-adrenoceptor/cAMP/PDE pathway. Signals, such as epinephrine (adrenaline), bind to beta-adrenoceptors and cause adenylyl cyclase, an enzyme that catalyzes the production of cAMP, to become more active. The presence of cAMP then triggers a cellular response. Phosphodiesterase (PDE) catalyzes the degradation of cAMP.

In this study, researchers were curious about how the density of cell cultures (how closely packed cells are in a culture dish) influences the beta-adrenoceptor/cAMP/PDE pathway. The researchers did one experiment ( Fig 1 cAMP production (reflected as % increase in cAMP) in response to adding 100 nM isoprenaline in low density (LD) and high density (HD) cell cultures) where they added isoprenaline, which binds to and activates the beta-adrenoceptor in the same way adrenaline does. After adding isoprenaline, the percent increase in cAMP in HD and LD cell cultures was measured, as shown below.

What can the researchers conclude from their study?

Answer 1

Though the figure has not shown here, I am explaining the conclusion:

Isoprenaline has the similar effect as adrenaline does on the beta-adrenoceptor in low density (LD) and high density (HD) cell cultures. Chemically synthesized analog of adrenalin (isoprenaline) acts as an agonists to mimic the normal function of the hormone by binding to its receptor and leading to the normal response. β-adrenergic receptors are coupled with stimulatory G protein (G_s). The binding of adrenalin or isoprenaline to β-adrenergic receptors leads to an elevation of intracellular cAMP level. Activation of adenylyl cyclase leads to the conversion of ATP to cAMP and pyrophosphate (PP_i). The G_s helps the hormone (or chemical compound) to link with an exterior domain of the receptor, and it also facilitates the activation the adenylyl cyclise that triggers a signal transduction.