Schild's equation and the best estimate of pA(2) value and dissociation constant of an antagonist

Calculation of the pA2 value and dissociation constants for an antagonist f rom the effects observed on isolated smooth muscles can be done in two ways : using Schild's plot procedure or Schild's equation. In our study we used the effects of muscarinic antagonists observed in experiments on isolated h uman and feline stomach and rat gastric fundus. Only the estimates of pA2 v alues and dissociation constants made using the Schild's equation on the ba sis of the lowest antagonist concentrations were not significantly differen t from the values calculated using the Schild's plot procedure. This sugges t that, when it is impractical to perform the full Schild's plot procedure, the best estimate of pA2 values and dissociation constants can be done wit h the lowest antagonist concentration that significantly inhibits the effec ts of an agonist on an isolated smooth muscle preparation.