Fain J N, Berridge M J
Biochem J. 1979 Jan 15;178(1):45-58. doi: 10.1042/bj1780045.
The addition of 5-hydroxytryptamine to the isolated blowfly salivary gland stimulates fluid secretion, transepithelial calcium transport and the breakdown of 32P- or 3H-labelled phosphatidylinositol The breakdown of [32P]phosphatidylcholine and [32P]-phosphatidylethanolamine was not stimulated by 5-hydroxytryptamine. In salivary glands incubated with myo-[2-3H]inositol for 1--3 h, more than 95% of the label retained by the tissue was in the form of phosphatidylinositol. The addition of 5-hydroxytryptamine resulted in an increase in the accumulation of label in intracellular inositol 1:2-cyclic phosphate, inositol 1-phosphate and free inositol along with an increase in the release of [3H]inositol to the medium and saliva. The release of [3H]inositol to the medium served as a sensitive indicator of phosphatidylinositol breakdown. The release of [3H]inositol was not increased by cyclic AMP or the bivalent-cation ionophore A23187 under conditions in which salivary secretion was accelerated. The stimulation of fluid secretion by low concentrations of 5-hydroxytryptamine was potentiated by 3-isobutyl-1-methylxanthine, which had no effect on inositol release. The stimulation of fluid secretion by 5-hydroxytryptamine was greatly reduced in calcium-free buffer, but the breakdown of phosphatidylinositol continued at the same rate in the absence of calcium. These results support the hypothesis that breakdown of phosphatidylinositol by 5-hydroxytryptamine is involved in the gating of calcium.
向离体的家蝇唾液腺中添加5-羟色胺可刺激液体分泌、跨上皮钙转运以及32P或3H标记的磷脂酰肌醇的分解。5-羟色胺不会刺激[32P]磷脂酰胆碱和[32P]磷脂酰乙醇胺的分解。在与肌醇-[2-3H]一起孵育1至3小时的唾液腺中，组织保留的超过95%的标记物是以磷脂酰肌醇的形式存在。添加5-羟色胺会导致细胞内肌醇1:2-环磷酸酯、肌醇1-磷酸酯和游离肌醇中标记物的积累增加，同时向培养基和唾液中释放的[3H]肌醇也增加。向培养基中释放[3H]肌醇是磷脂酰肌醇分解的敏感指标。在唾液分泌加速的条件下，环磷酸腺苷或二价阳离子载体A23187不会增加[3H]肌醇的释放。低浓度的5-羟色胺对液体分泌的刺激作用会被3-异丁基-1-甲基黄嘌呤增强，而3-异丁基-1-甲基黄嘌呤对肌醇释放没有影响。在无钙缓冲液中，5-羟色胺对液体分泌的刺激作用大大降低，但在没有钙的情况下，磷脂酰肌醇的分解仍以相同的速率继续。这些结果支持了5-羟色胺引起的磷脂酰肌醇分解参与钙门控的假说。
