Functional basis of molecular diseases
1. Introduction
To produce a therapeutic/beneficial effect or minor, major, serious and severe toxic effects, drugs interact with receptors, ion channels, membrane carriers or enzymes in the body; this is the pharmacodynamic phase of drug action. The drug in the tissues, where drug-receptor interactions usually occur, is in equilibrium with the unbound drug in the plasma. Drugs interact in a structurally specific way with these protein receptors. RECEPTORS are the class of cellular macromolecules that are concerned specifically and directly with chemical signalling between and within cells. endogenous ligands like a hormone, neurotransmitter, or intracellular messenger when combined with its receptor(s), it results in a cellular activity change. A general property of all receptors is the ability to interact with their endogenous ligands (hormones and neurotransmitters) to alter cellular responsiveness without changing the chemical nature of the ligand. Hence, a receptor must not only recognize the particular molecules that activate it but also, when recognition occurs, alter cell function by causing, for example, a change in membrane permeability or an alteration in gene transcription.
Therapeutic and toxic effects of a drug result from the interaction between the drugs with a macromolecules/receptors and further altering the biophysical and biochemical activities of the macromolecules. Receptors have become the central focus of an investigation of drug response and their mechanism of action. The receptor concept has important practical consequences for the development of drugs and for arriving at therapeutic decisions in clinical practice.
Drug-receptor complex presents three important elements (i) receptors as determinants of the quantitative relation between the drug concentration and pharmacological response. (ii) Receptors are regulatory proteins that provide a target for the drugs. (iii) Receptors are the key determinant of therapeutic and toxic response in a patient. The relation between dose of a drug and therapeutic response is complex in a patient, however, the relation between concentration and therapeutic effect in an in vitro system is often simple and described in a concentration-response curve (dose-response curve).
The two properties of a drug that determine the nature of its interaction with the receptor are it’s:
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