Answer:
The correct answer is ''G-protein coupled receptors on the surface of cardiac muscle cells.''
Step-by-step explanation:
Adrenaline is a catecholamine whose pharmacological effects occur at alpha and beta adrenergic receptors. The mechanism of action of all beta adrenergic receptors is the activation of a G protein that activates adenylyl cyclase and increases cyclic AMP production. Adrenaline by b-adrenergic stimulus increases the contractile force of the myocardium (positive inotropic action) and increases the frequency in which the myocardium contracts (positive chronotropic action), consequently there is an increase in cardiac work, with a greater demand for oxygen due to the myocardium to be able to contract. Therefore, the blood flow to the heart is indirectly increased, bringing with it a greater supply of oxygen.