Receptor-Mediated Cell Signaling Flashcards Preview

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Flashcards in Receptor-Mediated Cell Signaling Deck (17):


Block receptors and have no inherent ability to elicit a response


Competitive antagonist

molecule that competes for the same binding site as an agonist; low concentrations can be overcome by the agonist; effects depend upon its concentration which is influenced by the rate of metabolic clearance or excretion


Non-competitive antagonist

  • have depressive effects on maximal agonist response but do not compete for same binding site as the agonist
  • blockade is fixed and cannot be overcome by the agonist
  • usually have prolonged effects and receptor blockade reversal is slow
  • duration of action depends upon rate of receptor turnover
  • Ex: ketamine blocks channel functioning of NDMA receptor channel for glutamate


Chemical antagonist

a drug that binds directly to an agonist and deactivates the agonist (form an inactive compound) e.g. tannins


Physiological antagonist

any drug or chemical that has an opposite effect, but through different physiological pathways e.g. histamine and epinephrine (contract vs. dilate sm mm of airway)


Pharmacologic antagonist

any drug that binds to a receptor and prevents the activation of the receptor


Drug-Receptor Interactions

  • most drugs bind in reversible manner - unbinding and binding occurs very fast
  • drug binding chemical interaction is determined by structure of drug relative to receptor binding site


Properties of drug-receptor interactions:

  1. Saturable (maximal) response (finite # of receptors)
  2. Reversibility
  3. Good potency (many drugs act @ very low concentrations)
  4. Chemical sensitivity 
  5. Competitive blockade by antagonists
  6. Amplified responses


Dissociation constant (Kd)

  • the concentration at which 50% of the binding sites (receptors) are occupied by the drug; can be determined for an agonist or antagonist
  • expressed as a concentration
  • provides info about affinity of the drug for a receptor
  • High affinity - low Kd; Low affinity - high Kd



how well a drug binds a receptor; helps define the drug's potency



amount of drug required to produce a desired effect; used as means to compare drugs, (higher potency, less drug required)



drug concentration producing 50% of a maximal effect; typically used for in vitro  studies



the maximum effect a drug can produce


for drugs w/ similar maximal efficacy, increasing drug potency decreases EC50


ED50 or effective dose

dose that causes a desired effect in 50% of the population receiving it; effect must be all or none (quantal effect)



measure of a drug's ability to produce a desirable effect relative to its ability to produce an undesirable effect


Specificity = ED50 (desirable)/ ED50 (undesirable)


If ED50 (un) >>>ED50 (des) = high (good) specificity

If ED50 (un) = ED50 (des) = low (bad) specificity


Therapeutic Index (TI)

a quantal response; ratio of LD50 (lethal dose in 50%) and ED50; the larger the TI, the safer the drug is


TI = LD50/ED50


Margin of Safety

ratio of drug that is just within the lethal range (1%) to the dose that is 99% effective; more stringent index of safety


MOS = LD1/ED99