Pharmacodynamics is a branch of Pharmacology that deals with pharmacological effects, mechanisms, sites and types of action of medicinal substances.
Pharmacological effects of MS are changes in the functions of the body?s organ system-sin response to the MS.
MS mechanisms of action are ways through which the substances exert pharmacological effects. The main molecular targets of medicinal substances are the following structures:
• receptors;
• enzymes;
• ion channels;
• transport systems. Receptors are functionally active macro-
molecules ensuring cellular response to the action of transmitters or other substances. Their binding to the receptor-specific affinity substances (ligands) causes conformational changes of receptor protein, and initiates a chain of cellular biochemical reactions leading to certain effects on tissues, organs, and systems (pharmacological effects, if the ligand is a medicinal agent). Receptors serve as targets for either endogenous ligands (neurotransmitters, hormones, cytokines and other endogenous biologically active substances), or exogenous biologically active substances (including drugs). There are four types of receptors (fig. 1.1):
• ligand-gated ion channels, also termed iono-tropic receptors (see fig. 1.1, а);
• G-protein coupled receptors, also termed metabotropic receptors (see fig. 1.1, b);
• Enzyme-linked receptors (e.g. tyrosine ki-nase) (see fig. 1.1, c);
• Intracellular receptors (receptors regulating transcription of genes) (see fig. 1.1, d). А. Ion channel coupled receptors. After
binding of an agonist or an antagonist to an ion channel receptor, the transmembrane conductance of specific ions increases or decreases within milliseconds, causing a change in the cell membrane electrical potential. Vital activity of the cell strongly depends on Na+, К+, Cа2+, Cl-, and H+ ions. Passage of ions through channels is affected by many antiarrhythmic drugs [Procainamide (Novocainamide♠), Amiodaron, and others)], local anesthetics [Procaine (Novocain♠), Lidocaine], anticonvulsants (Phe-nytoin, Carbamazepine, Lamotrigine). The same mechanism of action is typical of drugs which block calcium channels (Verapamil, Nifedipine, Diltiazem), and activate potassium channels (Minoxidil).