How Drugs Act

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Targets can be divided into four categories…
Ion Channels
Their modulation by drugs is very important mechanism by which pharmacological actions are produced . 1. Voltage gated Na2+ channels ( local anesthetic)
2. Calcium channels ( Ca2+ channel blockers) 3. K+ channels ( in pancreatic β-cells) Enzymes
* Many enzymes are targets for drugs
* Drug molecules can act as competitive inhibitor of the enzyme e.g. neostigmine acting on cholinesterase enzyme * Other drugs may inhibit enzymes non-competitively e.g. aspirin, acting on cyclooxygenase enzyme Carrier proteins (transporters)

# The transport of ions and small organic molecules across cell membranes generally requires a carrier protein, because these are often too polar (i.e. insufficiently lipid-soluble) to penetrate lipid membranes on their own. e.g. Tricyclic antidepressants act on the reuptake of noradrenaline, 5 HT transporters Receptors

* Serve as recognition sites for specific endogenous compounds such as: 1. Neurotransmitters, e.g. noradrenaline
2. Hormones (thyroid hormones)
3. Local Hormones /Autacoids (released and act upon the same/nearby tissue, e.g. prostaglandins) Drug Receptors
Most drugs exert their effects, by interacting with receptors present on the cell surface or intracellularly Action occurs when drug binds to receptor and this action may be: Ion channel is opened or closed

Second messenger is activated
cAMP, cGMP, DAG, inositol trisphosphates (IP3), etc.
Normal cellular function is physically inhibited
4 main receptor categories
Most signal molecules targeted to a cell bind at the cell surface to receptors embedded in the plasma membrane e.g. ligand-gated ion channels, G-protein coupled receptors, kinase –linked receptors Only signal molecules able to cross the plasma membrane (e.g. steroid hormones) interact with intracellular receptors (Nuclear receptors) Types of Receptor (4)...
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