ABSTRACT
B. Clark Analysis Schild analysis should only be used as a method of K8 estimation when a concentration ratio (r) can be estimated from a single experiment, 'that is, when a multiple curve design is employed (see Section V). This allows an intratissue comparison of the E/[A] curves obtained in the absence and presence of the antagonist to be made. In contrast, when a single-curve design is used, calculation of r values necessitates referring the location of each displaced curve to the same control curve location. Schild analysis of such data is statistically flawed because it overweights the control data. This problem can be overcome by using a modified version of Eq. (11), which analyzes location ([A]s0) values rather than concentration-ratios:
logto[A]so = logw[A]~ + logto(1 + [B]n/Ks) (13) This so-called Clark analysis (37-39) involves fitting E/[A] curve location parameters obtained in the absence ([A]~ 0 ) and presence ([A]s0) of antago-
of the two individual agonist E/[AJ curves that make up the overall relaxant curve of a = 13.7 :t 1.5. The antagonist, which has a higher affinity for receptor type Q, shifts the curve to the right until it reaches the concentration range in which receptor type R contributes significantly to the observed response. The E/[A] curve then appears to hit a barrier (corresponding to the inflexion in the Schild plot), which is overcome only when the antagonist concentration exceeds that needed to block the second receptor. (From Ref. 42, reprinted by permission of the publisher. Copyright 1996 by Elsevier Science Inc.)
