CHARACTERISTICS OF MUSCARINIC CHOLINOCEPTORS IN AIRWAYS OF ANTIGEN-INDUCED AIRWAY HYPERRESPONSIVE RATS

The antagonist and agonist binding sites of muscarinic receptors were investigated by using membrane preparations of airways from nonsensiti zed normal control, sensitized control and repeatedly antigen challeng ed rats. The in vitro bronchial responsiveness to ACh was markedly inc reased in repeatedly antigen challenged group but not in sensitized co ntrol group. No significant difference was observed in receptor densit y and antagonist affinity among these three groups. The affinity of AC h for high-affinity agonist binding sites of repeatedly antigen challe nged group was much greater than those in the other groups; the affini ty significantly reduced in the presence of GTP gamma S. We concluded that enhanced G protein level might be involved in inducing airway hyp erresponsiveness in rats.