Receptortypes

Receptortypes describe the categories of receptors in biological systems that detect external or internal signals and initiate cellular responses. They are commonly classified by location into cell-surface receptors, which reside on the plasma membrane, and intracellular receptors, which act within the cytosol or nucleus after ligand entry.

Cell-surface receptors include ligand-gated ion channels, G protein-coupled receptors (GPCRs), and enzyme-linked receptors such as receptor tyrosine kinases. Ion channels convert chemical signals into changes in ion flow. GPCRs activate heterotrimeric G proteins to trigger second messengers like cAMP, IP3, and Ca2+. Enzyme-linked receptors have intrinsic enzymatic activity or recruit kinases; receptor tyrosine kinases are a prominent subset.

Intracellular receptors bind lipophilic ligands that cross membranes, such as steroid hormones, thyroid hormones, and certain lipophilic gases. These receptors often function as transcription factors that regulate gene expression.

Receptortypes also differentiate by the ligands they recognize, including small molecules, peptides, proteins, ions, and nucleotides. Signal transduction mechanisms vary from rapid ion flux to slower transcriptional changes.

Understanding receptortypes informs physiology, pharmacology, and drug development, as selective targeting of receptor subtypes can modulate specific pathways while minimizing side effects. Classic receptor subclasses include adrenergic GPCRs, tyrosine kinase receptors, and nuclear receptors, each with characteristic signaling cascades and regulatory properties.