title: Effects of cooling on the contractile response of the rat tracheal muscle to pilocarpine in vitro.
abstract: Experiments were designed to determine the effect of cooling on the contractile response of rat tracheal strip-chain preparation to the partial agonist pilocarpine. The preparation was suspended in an organ bath containing Krebs bicarbonate solution for isometric tension recording. A decrease of the bath temperature from 37 to 30, 20 or 10 degrees C (cooling) did not affect or inhibited the contractile response of the trachea caused by pilocarpine (1-100 microM), while it augmented the carbachol (0.1-1 microM)-induced response. At 37 degrees C, the pilocarpine (3-100 microM)-induced contraction was relatively resistant to removal of extracellular Ca2+ or to the Ca2+ entry blocker, verapamil (1 microM). Similar results were also obtained for the carbachol (0.3-10 microM)-induced response. On the other hand, the affinity of pilocarpine for the tracheal muscarinic receptors, determined from its dissociation constant (KA), was significantly decreased at a lower temperature. It is concluded from these observations that cooling-induced subsensitivity of the rat tracheal muscle to pilocarpine is mainly associated with a decrease in the affinity of the agonist for muscarinic receptors.
mesh_terms: D000818:Animals; D001285:Atropine / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D002217:Carbachol / Q000494:pharmacology; D003080:Cold Temperature; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects*; D010830:Physostigmine / Q000494:pharmacology; D010862:Pilocarpine / Q000494:pharmacology*; D051381:Rats; D011919:Rats, Inbred Strains; D011976:Receptors, Muscarinic / Q000187:drug effects; D013779:Tetrodotoxin / Q000494:pharmacology; D014132:Trachea / Q000187:drug effects; D014700:Verapamil / Q000494:pharmacology
chemical_list: D011976:Receptors, Muscarinic; D010862:Pilocarpine; D013779:Tetrodotoxin; D001285:Atropine; D002217:Carbachol; D010830:Physostigmine; D014700:Verapamil; D002118:Calcium