Compare and contrast the mechanism of action of ion channel-coupled receptors, G-protein-coupled receptors, and enzyme-coupled receptors.
a) Ion channel-coupled receptors directly affect intracellular enzymes, while G-protein-coupled receptors and enzyme-coupled receptors do not.
b) G-protein-coupled receptors and enzyme-coupled receptors involve the activation of second messengers, while ion channel-coupled receptors do not.
c) Ion channel-coupled receptors primarily activate G-proteins, whereas G-protein-coupled receptors directly affect ion channels.
d) Enzyme-coupled receptors involve the direct opening of ion channels, unlike G-protein-coupled receptors and ion channel-coupled receptors.
