Lecture-11 - Total drug binding increases with the addition...

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Total drug binding increases with the addition of increasing concentrations of radioligand. However, this reflects non- specific binding to non-receptor molecules such as other proteins as well as membrane lipids. Question: How do we determine binding of drug that is specific to its receptor? A second set of tissue samples is assayed using the same concentrations of radioligand, but this time in the presence of an excess concentration of unlabeled ‘cold’ drug. In the presence of excess cold drug, the specific binding sites will be saturated and the binding that is observed is to the relatively unlimited number of nonspecific sites. Specific binding = total binding minus non-specific binding.
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An analogy to help you understand specific and non- specific binding. Scenario 1: There are 10 chairs (drug receptors) in the middle of a huge field. 1000 people in red shirts (hot drug) compete to sit in the 10 chairs. 10 sit in the chairs (specific binding) and 1% of 990 (10 people) sit on the ground (nonspecific binding) while 980 remain standing (unbound). Anyone sitting down contributes to total binding (20 people). Removing the 980 standing people is equivalent to washing tissue to
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Lecture-11 - Total drug binding increases with the addition...

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