The use of guinea pig K+-depolarized tracheal chain preparations in beta-adrenoceptor studies

Guinea pig tracheal chain preparations were K+-depolarized using Krebs solution in which all the Na+ was replaced by an equivalent amount of K+. This caused a sustained contraction of the preparations. Reproducible concentration-response (relaxation) curves to isoprenaline could be obtained provided that the preparations were repolarized by washing in normal Krebs solution between curves. pA2 values for propranolol (8.30) and butoxamine (5.89) were in good agreement with values obtained on other types of tracheal preparation. The maximum relaxation to salbutamol was less than that to isoprenaline and the maxima to both drugs were less than the maximum relaxation of the tissue (to papaverine). It is suggested that K+-depolarized tracheal preparations have no beta-adrenoceptor reserve and may, therefore, be useful in studies designed to compare the efficacies of beta-adrenoceptor agonists.