plot is known as the Schild plot 1 We can distinguish the fo

plot is known as the Schild plot [1]. We can distinguish the following possible cases: The Schild plot yields the expected straight line, and the unknown drug is the inhibitor. We can assume that the unknown drug binds to the same receptor as the known agonist and obtain its binding constant from the x axis intercept, which occurs at - logK_1. The Schild plot yields the expected straight line, and the unknown drug is the agonist. We then still can assume that it binds to the same receptor as the known antagonist; however, we will not know its binding constant. The latter could be determined by comparison with known agonists. The Schild plot does not yield the expected straight line. Then, we have to conclude that the two drugs do not bind competitively and may interact with different receptors. The plot below shows the contraction of smooth muscle isolated from pig small intestine in response to the drug carbamoylcholine, without pretreatment (control), after pretreatment with inhibitor A alone (A), or with both inhibitor A and inhibitor B (A+B). Let\'s assume that the amounts of A and B used were saturating, that is, increasing their dosages further would not change the observed response. How can we explain the observed behavior of this system? Is the inhibition exerted by A reversible or irreversible? What about B? The effect of a combination of two drugs can be examined using a so-called isobologram. The concentrations of each of the two drugs is independently varied, and the strength of the observable effect is measured. Curves connect points with equal strength of effect (see sketch below).

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2.1 in this Schild Plot the muscle cells when treated with drug, carbamoylcholine (CC) shows dose response and saturates the binding to the receptor. whereas pretreatment with antagonist A shows no change in observed binding of CC. that means both of them are binding to different receptors and they are competing to the same site and they are not reversible. if the inhibitor A has to show come competitive binding the curves should shift right. which is not happening. where as for Inhibitor B shows straight line and there is a reversible binding and also it is binding to same site as drug.

2.2 the question in this discuission is not provided and there is just explanation of isobolograms.