2. Introduction to Drug-Receptor Interactions and Pharmacodynamics

Receptors: protein molecules including enzymes, transporters and ion channels where a ligand (specific endogenous neurotransmitter/hormone or an external pharmacological agent (drug)) binds to, resulting in a cellular response.

• Unique Exception: Orphan Receptors are receptors for which the ligand remains unknown.
• Reminder: Ligand is an ion or molecule that forms a complex with a biomolecule to serve a specific biological purpose

Examples of Endogenous Ligands:

• • Neurotransmitters[NT]: chemical messengers signaling across a synaptic cleft
    • Acetylcholine [Ach]
    • Epinephrine [EPI]
    • Norepinephrine [NE]

• • Hormones (peptide): secreted from neuroendocrine cells into the blood to signal at distant cells and tissues.
    • Aldosterone
    • Insulin
    • Nerve growth factor [NGF]
    • Thyroid hormone [TH]

• Insulin is synthesized and released by pancreatic beta cells. It is transported through the blood to a variety of cells to stimulate those cells to express glucose transporters allowing those cells to bring glucose into the cell for energy utilization.

DRUG: A chemical agent that selectively interacts with specific target molecules (i.e. receptors) to alter their specific physiological functions.

• Agonist: drug that activates receptors to result in either stimulation or inhibition of the function of various types of cells and organs.
• Antagonist: drug that prevents receptor activation by agonists.

Drug-Receptor Binding: drugs bind to their respective receptor in a variety of ways depending on their characteristics.

• Ionic interaction: cation & anion
• Hydrogen bonding
• Lipophilic interaction
• Covalent bond: irreversible