National Nursing Review : Nursing Study Resources & Health Tips

Few drugs, if any, have absolute specificity, but most features on selectivity, eg., Atropine inhibits the action of acetylcholine on smooth muscle and exocrine glands, but not the skeletal muscle. The selective action of these drugs is due to their physical-chemical bond with cellular components known as receptors. The receptors are physiological molecules involved in transmitting chemical signals between a cell and another and within cells. A molecule that binds to a receptor is defined ligand. When a ligand (hormone, neurotransmitter, drug or intracellular messenger exogenous) combines with a receptor cell function is changed, each ligand can interact with multiple receptor subtypes. The receptors activated directly or indirectly regulate cellular biochemical processes (eg., Ion conductance, protein phosphorylation, transcription of DNA). In many cases, the receptors located within the cell membrane are coupled through the guanine nucleotide binding proteins (G proteins) with different effector systems involving molecules that act as intracellular second messengers.

The receptors are dynamic structures, affected by both external factors and by intracellular regulatory mechanisms. The up-regulation and down-regulation of receptors relate phenomena of adaptation to drugs which have important clinical implications (desensitization, tolerance, acquired resistance, hypersensitivity to suspension).

The specific regions of macromolecules molecular receptor which binds the ligand recognition sites are called. A drug may interact at the same site which interacts with an endogenous agonist (hormone or neurotransmitter) or at a different site. Agonists that bind to adjacent sites or different allosteric agonists are sometimes called. The drugs are also linked in a non-specific, ie not at the molecular features of sites like receptors (eg., Plasma proteins). (more…)