Both function by binding to protein receptors on cells. The four primary receptors — alpha-1, alpha-2, beta-1, and beta-2 — are located in different body areas. The impact of norepinephrine ...

G-protein coupled receptors regulate hormone secretions ... Within islets, beta cells secrete insulin, and alpha cells secrete glucagon. Scientists have identified three additional cell types ...

In unstimulated cells, the state of G alpha (orange circles) is defined by its interaction with GDP, G beta-gamma (purple circles), and a G-protein-coupled receptor (GPCR; light green loops).