A. RECEPTORReceptors are macromolecules involved in chemical signaling between and within cells; they may be located on the cell surface membrane or within the cytoplasm .Activated receptors directly or indirectly regulate cellular biochemical processes (eg, ion conductance, protein phosphorylation, DNA transcription, enzymatic activity). Molecules (eg, drugs, hormones, neurotransmitters) that bind to a receptor are called ligands. A ligand may activate or inactivate a receptor; activation may increase or decrease a particular cell function. Each ligand may interact with multiple receptor subtypes. Few if any drugs are absolutely specific for one receptor or subtype, but most have relative selectivity. Selectivity is the degree to which a drug acts on a given site relative to other sites; selectivity relates largely to physicochemical binding of the drug to cellular receptors.A drugs ability to affect a given receptor is related to the drugs affinity (probability of the drug occupying a receptor at any given instant) and intrinsic efficacy (intrinsic activitydegree to which a ligand activates receptors and leads to cellular response). A drugs affinity and activity are determined by its chemical structure.The drug works by getting involved in the interaction between endogenous chemical compounds with these receptors, either stimulating (agonist) or prevent the interaction (antagonist)Type of receptors1. ligand-gated ion channelsThis receptor is located in the cell membrane, called receptors ionotropik. Response occurred in a matter of milliseconds. have thereceptorand transducing functions as part of the same protein molecule. Interaction of the chemical signal with the binding site of the receptor causes the opening or closing of an ion channelporein another part of the same molecule. The resulting ion flux changes the membrane potential of the target cell and, in some cases, can also lead to entry of Ca2+ions that serve as a second messenger signal within the cell. Good examples of such receptors are the neurotransmitter receptorsExample: nicotinic receptors, GABAA receptors, glutamate receptors and receptor 5- ionotropik HT3.

2. Receptors linked enzymeEnzyme linked receptor is a transmembrane protein with a large sectioncontaining the extracellular ligand binding site for (eg growth factors, cytokines)and the intracellular portion having enzyme activity (usually a tyrosine kinase activity).Initiate activation of intracellular pathways involving cytosolic and nuclear transducer,even gene transcription. Cytokine receptor activates Jak kinase, which in turnStat activate transcription factors, which then activates gene transcription

3. G-protein-linked receptorsGPCR, called receptors metabotropik, located in the cell membrane and responseoccur in a matter of seconds. GPCR has a single polypeptide chain with seven helicaltransmembrane. Signal transduction occurs by activation of G-protein part latermodulate / regulate enzyme activity or function of the canal

4. Gene transcription linked receptorsReceptors linked gene transcription is also called nuclear receptors (although somein the cytosol, the cytosolic receptors which then migrate to the nucleus afterbind to the ligand, such as the glucocorticoid receptor). Example: corticosteroid receptors,estrogen and progestogen receptors

Drug receptor interactionsLigands such as hormones or neurotransmitters like a key that binds thespecific receptor (which acts as a keyhole). This interaction opens the cell's response.Drug-like ligand, when interacting with the same receptor responds withligand, an agonist that can be unlocked. Other drugs that work againstcalled antagonists.