title: Differential development of carbachol-induced desensitization in receptor-mediated Ca2+ influx and Ca2+ release pathways in smooth muscle of guinea-pig taenia caeci.
abstract: 1. We have found that development of carbachol (CCh)-induced desensitization to receptor agonists, but not to receptor by-passed stimulation, is transiently interrupted by a Ca2+-dependent resensitization during the early stage in the smooth muscle of guinea-pig taenia caeci. To further characterize the receptor-mediated signal transduction pathways involved in this peculiar desensitization process, we examined the desensitization processes during Ca2+ influx- and Ca2+ release-mediated contractions in response to activation of muscarinic receptors or histamine H1 receptors. 2. Desensitization treatment with 10(-4) mol/L CCh for 30 min in the presence of extracellular Ca2+ resulted in desensitization to the muscarinic agonists McN-A-343 or AHR-602, which are known to induce contraction only in the presence of extracellular Ca2+ in taenia caeci. The development of desensitization to these agonists was interrupted by a transient resensitization at 1 min. In contrast, the transient resensitization phase was lost following removal of extracellular Ca2+ during the desensitization treatment with CCh; under these conditions, the desensitization developed gradually without an apparent resensitization phase. 3. Contractions to 10(-4) mol/L CCh and 10(-4) mol/L histamine in the absence of extracellular Ca2+ were gradually desensitized without a resensitization phase following the CCh desensitization treatment, irrespective of the presence or absence of extracellular Ca2+ during CCh treatment, although the onset of the desensitization was delayed under Ca2+-free conditions. 4. These results suggest that the receptor-mediated Ca2+ influx and Ca2+ release pathways are differentially desensitized to CCh and that the transient resensitization appears to regulate the desensitization process in response to Ca2+ influx-mediated contraction. Such differential processes of desensitization in receptor-mediated bifurcated signalling pathways may determine cellular responsiveness to certain types of stimuli, depending on the different Ca2+ sources required for contraction.
authors.affiliation: Department of Pharmacodynamics, Meiji Pharmaceutical University, Tokyo, Japan. hishi@my-pharm.ac.jp
authors.forename: Shigeru
authors.initials: S
authors.lastname: Hishinuma
authors.forename: Yukio
authors.initials: Y
authors.lastname: Matsumoto
authors.forename: Ryo
authors.initials: R
authors.lastname: Sato
authors.forename: Masaki
authors.initials: M
authors.lastname: Saito
mesh_terms: D008455:(4-(m-Chlorophenylcarbamoyloxy)-2-butynyl)trimethylammonium Chloride / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects*; D002217:Carbachol / Q000494:pharmacology*; D002432:Cecum / Q000187:drug effects / Q000378:metabolism*; D005260:Female; D006168:Guinea Pigs; D006632:Histamine / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D018721:Muscarinic Agonists / Q000494:pharmacology*; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000378:metabolism*; D011759:Pyrrolidines / Q000494:pharmacology; D020239:Receptor Cross-Talk / Q000187:drug effects
chemical_list: D018721:Muscarinic Agonists; D011759:Pyrrolidines; C004296:N-benzyl-3-pyrrolidylacetate methobromide; D008455:(4-(m-Chlorophenylcarbamoyloxy)-2-butynyl)trimethylammonium Chloride; D006632:Histamine; D002217:Carbachol; D002118:Calcium