Kd= dissociation constant R = receptor R+ L RL L- ligand off IRIL Total Rec: R,-

Question

Kd= dissociation constant R = receptor R+ L RL L- ligand off IRIL Total Rec: R,- IRI+ IRL] d- [RL] RL Kd ILI QUESTIONS You've identified a drug that has the potential to bind and inhibit 5 different histamine receptors found on human mast cells. The drug if ingested orally typically reaches a concentration of 1 x 10 Molar in the blood stream. Given the Kd of the drug for each of the 5 receptors listed below, calculate the percentage of receptors occupied with a drug concentration of 1 X 10-8 Molar. Percentage of Receptors Occupied (with 108 Molar drug concentration) RECEPTOR Receptor A Kd 1 micromolar Receptor B Kd 10 micromolar Receptor C K, = 100 micromolar Receptor D Ks 1 nanomolar Receptor E Kd 10 nanomolar

Explanation / Answer

Formula : { [C] / [C] + Kd } * 100 , where C = 10-8 M = drug conc
1 Micromolar = 1*10-6 Molar ; 1 Nanomolar = 1*10-9 Molar
Receptor A :
% of receptor occupied = [10-8M / (10-8 + 10-6) ] *100 = 0.9999 %
Receptor B:
% of receptor occupied = [10-8M / (10-8 + 10 * 10-6) ] *100 = 0.0999 %
Receptor C :
% of receptor occupied = [10-8M / (10-8 + 100*10-6) ] *100 = 0.00999 %
Receptor D :
% of receptor occupied = [10-8M / (10-8 + 10-9) ] *100 = 90.9090 %
Receptor E :
% of receptor occupied = [10-8M / (10-8 + 10*10-9) ] *100 = 50 %

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