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| Questão | Responda |
| Receptors | - Receptors are protein macromolecules, usually inserted across the lipid bilayer of the cell - Perform 2 functions: 1. Recognition/detection of other molecules 2. Transduction - Receptors interact with/bind with certain chemicals with a high degree of specificity - Receptors are classified with respect to the drugs they bind: eg nicotinic acetylcholine receptors - Pharmacologists aim to design drugs that only bind to certain subtypes of receptor; leading to fewer side-effects, so the drugs are more selective in their action. |
| Binding of drugs to receptor | Drug=D Receptor= R D+R(reversible-reaction)DR - In most cases, binding is reversible - The plot of the proportion of receptors occupied vs drug concentration is a rectangular hyperbola - The plot of the proportion of receptors occupied (p) vs log (d) is a symmetrical sigmoid |
| Affinity and KD | - The affinity of a drug for its receptor: "the molar conc of a drug required to occupy 50% of the receptors at equlibrium" - The KD is the equilibrium dissasociate constant - At equilibrium, backwards rate=forwards rate - KD is a measure of chemical attraction, as receptors are constantly bombarded with chemicals, and only those with affinity bind. - The lower the Kd, the higher the affinity - Drugs with high affinity (low kd), stay bound fo =r a relatively long time |
| Affinity vs efficacy | - Having affinity: binding to receptor - Being an agonist (having efficacy): binding to and activating receptor (producing a conformational change that ultimately leads to a response in a cell or tissue.) - Activation of receptors (R) by angonist (A) produces a biological response A+R (reversible reaction) AR (reversible reaction) AR* -response - Efficacy is the ability of the drug to activate the receptor |
| Types of agonist | - Full agonists: have high efficacy, so are very effective at activating receptors to produce a biological response. Often produce a maximal response while only occupying a fraction of available receptors. - Partial agonists: have low efficacy so are less effective. Often fail to produce a full response despite occupying all available receptors. - Agonist response depends on efficacy AND affinity, while occupancy only depends of affinity. |
| Antagonists | - Antagonists act to inhibit the actions of a neurotransmitter, hormone or other drug - Many clinically useful drugs are antagonists - There are several distinct forms of antagonism |
| Forms of antagonism | - Chemical: the use of one drug to chemically inactivate another (receptors not involved). EG dimercaprol in arsenic posioning - Pharmacokinetic: where one drug alters the way the body (receptors not involved) EG antaacids preventing absorption of phenytoin into the gut. - Physiological: 2 drugs act, producing opposite effects, to cancel one another out EG noradrenaline increases HR while acetylcholine decreases it - |
| Forms of antagonism: competitive vs non-competitive | - Competitive antagonists: compete with agonist for the same site on the receptor molecule, without activating it. Has affinity but no efficacy. - Non-competitive antagonist- act at a different site on the receptor/another molecule closely associated with it |
| Reversible competitive antagonists | - Inhibit the effects of a neurotransmitter/hormone - Can be overcome by increasing the concentration of the agonist - Produce a parallel shift to the right of the agonist log conc vs response curve. |
| Irreversible competitive antagonist | - Also produce a shift in the agonist log concentration-response curve, but the shift is not paralle (ie not surmountable, lower) |
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