Chapter 58

Principles of Pharmacology and Medicinal Chemistry

Card 1 of 10Receptors and Signaling

Chapter Opening

🧬

How drugs talk to cells

Receptor Types

Receptors are protein or glycoprotein structures that receive and transmit information to alter cell behavior. The main classes are cell-surface receptors -- seven-transmembrane G protein-coupled receptors, ion channels, and growth factor receptors -- and intracellular receptors (cytoplasmic and nuclear). Microorganism proteins (cell wall transamidase, viral thymidine kinase) are selective drug targets because they differ structurally from human targets.

📡G protein-coupled receptors: seven transmembrane domains; use G-protein second messengers

🚪Ion channels: ligand-gated (nicotinic, GABA-A) and voltage-gated (Na, Ca, K)

📈Growth factor receptors: single transmembrane with cytoplasmic tyrosine kinase (EGF, insulin)

🧫Intracellular receptors: cytoplasmic (glucocorticoid) and nuclear (thyroid, steroids) act as transcription factors

Intracellular Receptors Change Gene Expression

Steroid (glucocorticoid) receptors are cytoplasmic until they bind hormone, then translocate to the nucleus to act as transcription factors. Nuclear receptors (thyroid hormone, sex steroids, retinoids) modulate gene expression directly. This is why steroid effects are slower in onset but longer lasting than membrane-receptor effects.

📖 “Receptors: protein/glycoprotein that transmit info. Cell-surface: GPCRs (7 transmembrane, G-protein second messengers), ion channels (ligand-gated nicotinic/GABA-A, voltage-gated Na/Ca/K), growth factor receptors (single transmembrane tyrosine kinase, EGF/insulin). Intracellular: cytoplasmic (glucocorticoid) and nuclear (thyroid, steroids) = transcription factors. Microorganism proteins = selective targets.”