Isoproterenol potentiates alpha -adrenergic and muscarinic receptor-mediated Ca2+ response in rat parotid cells |
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Authors: | Tanimura Akihiko; Nezu Akihiro; Tojyo Yosuke; Matsumoto Yoshito |
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Abstract: | The effects of the cAMP pathway on theCa2+ response elicited byphospholipase C-coupled receptor stimulations were studied in ratparotid cells. Although 1 µM isoproterenol (Iso) itself had no effect on the cytosolicCa2+ concentration, thepretreatment with Iso potentiatedCa2+ responses evoked byphenylephrine. The potentiating effect of Iso was attributed to ashifting of the concentration-response curves of phenylephrine to theleft and an increase in the maximal response. Half-maximal potentiationoccurred at 3 nM Iso. Iso also potentiated theCa2+ response elicited bycarbachol. The potentiating effect of Iso was mimicked by forskolin (10 µM) and dibutyryl adenosine 3',5'-cyclic monophosphate (2 mM) and was blocked by 10 µM H-89. Iso potentiated thephenylephrine-induced Ca2+response in the absence of extracellularCa2+, but Iso did not increase theinositol trisphosphate (IP3)production induced by phenylephrine. These results suggest that thepotentiation of the Ca2+ responsecan be attributed to a sensitization ofIP3 receptors by cAMP-dependentprotein kinase. |
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