graph of pA2

[biology_06er]

Hi there,

Besides using a schild plot, it says in our manual that it is possible to determine pA2 from hand drawn graphs?...can someone please explain how?...i hv the concs. of agonist and then the contraction % and then the contraction % of the same conc. of agonist in the presence of an antagonist? can sum1 pleeeease explain how to draw it by hand?

cheers,
b_06er

[blcr11]

Why can't you manually construct your own Schild plot from the data? You should have a series of %response vs [agonist] in the absence of and in the presence of several (hopefully at least three) different concentrations of antagonist. Find the dose ratios at the EC50s of the curves and then plot log(DR - 1) vs log([agonist]) concentrations. The x-intercept of this plot is Kd.

http://www.graphpad.com/curvefit/schild.htm

see figure 2 of this: http://jpet.aspetjournals.org/cgi/reprint/299/1/314

[biology_06er]

hey thanks...i was actually looking (still am looking) at that site b4 u posted...i get how to do it...but using the EC50 stuff i still end up doing the plot...in my book iit says"calculate pA2 values both ways for this lab, i.e one from each of ur hand-drawn graphs and one by shchild regression using ur data"...so atm ive produced a graph and found A'/A doses...am i combing by values from the EC50 graph to create a shild plot...hence in the end i will only end up with one pA2 value?...sorry if it snds dumbb

[blcr11]

I can be wrong, but I interpreted that to mean to estimate Kd by hand, and then compare it to a probably more accurate one determined by regression. Your prof may have to clarify what he/she wants you to do exactly if that's not it.