title: Ontogenesis of physiological responsiveness and guanine nucleotide sensitivity of cardiac muscarinic receptors during chick embryonic development.
abstract: Atria isolated from 4-day chick embryos were much less responsive to the negative chronotropic effect of muscarinic agonists than were atria from 5- or 8-day embryos, even though the density of muscarinic acetylcholine receptors (mAChR) was similar at all these ages. The mAChR in hearts from 4-day embryos were also significantly less susceptible to regulation of receptor number by in vivo agonist treatment and required a 2-5-fold greater dose of the muscarinic agonist carbachol to achieve a decrease in receptor number equivalent to that observed in 5- or 8-day embryonic hearts. When 4-day atrial membranes were assayed in physiological buffers, agonist binding to the mAChR was not regulated by GTP unless a sulfhydryl reducing agent was present. Receptors from 5- and 8-day embryos did not require addition of a sulfhydryl reducing agent in order to see guanine nucleotide effects on agonist binding. Even in the presence of a sulfhydryl reducing agent, carbachol binding to the mAChR in 4-day membranes was much less sensitive to guanyl-5'-yl imidodiphosphate (GppNHp) than binding to mAChR in 5- or 8-day membranes. In addition, forskolin-activated adenylate cyclase activity was much less sensitive to inhibition by GppNHp in membranes from 4-day atria than from 5- and 8-day atria. The GTP-binding component (NI) which couples the mAChR to inhibition of adenylate cyclase activity was examined by covalent modification with pertussis toxin.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D037361:Adenylate Cyclase Toxin; D000067956:Adenylyl Cyclase Inhibitors; D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D016275:Atrial Function; D001427:Bacterial Toxins / Q000494:pharmacology; D002217:Carbachol / Q000494:pharmacology; D002642:Chick Embryo; D003864:Depression, Chemical; D006150:Guanine Nucleotides / Q000494:pharmacology*; D006160:Guanosine Triphosphate / Q000494:pharmacology; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology; D006321:Heart / Q000196:embryology*; D006339:Heart Rate / Q000187:drug effects; D007545:Isoproterenol / Q000494:pharmacology; D009206:Myocardium / Q000378:metabolism*; D037342:Pertussis Toxin; D011813:Quinuclidinyl Benzilate / Q000378:metabolism; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000502:physiology*; D010566:Virulence Factors, Bordetella
chemical_list: D037361:Adenylate Cyclase Toxin; D000067956:Adenylyl Cyclase Inhibitors; D001427:Bacterial Toxins; D006150:Guanine Nucleotides; D011976:Receptors, Muscarinic; D010566:Virulence Factors, Bordetella; D006165:Guanylyl Imidodiphosphate; D011813:Quinuclidinyl Benzilate; D006160:Guanosine Triphosphate; D002217:Carbachol; D037342:Pertussis Toxin; D000262:Adenylyl Cyclases; D007545:Isoproterenol