Characterization of the Ca^<2+> Response Mediated by Activation of β-Adrenoceptors in Rat Submandibular Ducts

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The Ca2+ signaling mediated by activation of β−adrenoceptors was studied in a purified preparation of ducts from rat submandibular glands.At concentrations above 1 nM, isoproterenol(ISO)caused a small but significant increase in cytosolic Ca2+ concentration([Ca2+]i).The ISO−induced increase in [Ca2+]i was completely inhibited by the β−adrenoceptor antagonist propranolol but not by the α−adrenoceptor antagonist phentolamine.Forskolin was able to mimic the Ca2+ response to ISO.These results suggest that the ISO−induced increase in [Ca2+]i in rat submandibular ducts is mediated by an accumulation of cAMP resulting from activation of β−adrenoceptors.In the absence of extracellular Ca2+, ISO or forskolin caused a transient increase in [Ca2+]i, indicating Ca2+ mobilization from intracellular Ca2+ stores.Further, stimulation with ISO failed to mobilize Ca2+ after the depletion of intracellular Ca2+ stores by phenylephrine or carbachol, suggesting that the cAMP−mediated increase in [Ca2+]i is due to a Ca2+ release from inositol trisphosphate(IP3)−sensitive Ca2+ stores.As ISO did not stimulate a detectable production of IP3, the cAMP−mediated Ca2+ mobilization may be evoked by a mechanism different from activation of phosphoinositide hydrolysis.
社団法人日本薬理学会の論文
2000-09-01