Kopp R, Pfeiffer A
Dept. of Surgery, Klinikum Grosshadern, University of Munich, Germany.
Scand J Gastroenterol. 2000 Jul;35(7):686-93. doi: 10.1080/003655200750023336.
The functional role of the intracellular diacylglycerol/protein kinase C second-messenger pathway in the regulation of gastric acid secretion and the effects on the involved inositotrisphosphate/Ca2+/calmodulin system are not well understood, and contradictory data have been reported. We therefore evaluated the effects of phorbol ester treatment (tetradecanoylphorbol-12,13-acetate (TPA)) on dibutyryl cyclic adenosine-5' monophosphate (dBcAMP)- and carbachol-stimulated aminopyrine (AP) accumulation in comparison with intracellular alterations of the phospholipase C/inostol phosphate signal transduction pathway in isolated rat gastric parietal cells.
[14C]AP accumulation was determined as an indirect measure of gastric acid secretion. Inositolphosphate second-messenger activation was investigated with [3H]inositolmonophosphate release in [3H]-myoinositol prelabeled rat gastric parietal cells.
TPA at a low concentration of 5 nM caused a small (45%) but significant increase in carbachol (0.1 mM)-stimulated AP accumulation, which was dose-dependently inhibited by higher concentrations of TPA with corresponding shifts in the dose-response curve for carbachol-stimulated AP accumulation. AP uptake stimulated by dBcAMP (0.1 mM) and the synergistic stimulatory effect induced by carbachol together with dBcAMP were inhibited by TPA at all concentrations investigated. In the presence of increasing concentrations of the calcium ionophore ionomycin (10(-8)-10(-5) M) TPA at 5 nM increased AP accumulation (AP ratio was 4.02 with 5 nM TPA versus 1.23 in the absence of TPA; P < 0.05), indicating that phorbol ester stimulates AP uptake in rat parietal cells. Simultaneous investigation of [14C]AP accumulation and [3H]inositol monophosphate release showed that inhibitory effects of TPA on carbachol- and carbachol plus dBcAMP-stimulated cells are mediated by an inhibition of the receptor/G-protein/phospholipase C interaction, leading to a reduction of inositolphosphate release. The costimulation of rat parietal cells with dBcAMP, ionomycin, and TPA (5 nM) did not reproduce the synergistic effects of carbachol together with dBcAMP on AP accumulation, suggesting that carbachol-stimulated AP uptake seems to be additionally mediated by a still unknown pathway independent of intracellular calcium release or protein kinase C activation.
细胞内二酰基甘油/蛋白激酶C第二信使通路在胃酸分泌调节中的功能作用以及对所涉及的肌醇三磷酸/钙离子/钙调蛋白系统的影响尚未完全明确，且已有相互矛盾的数据报道。因此，我们评估了佛波酯处理（十四酰佛波醇-12,13-乙酸酯（TPA））对二丁酰环腺苷-5'-单磷酸（dBcAMP）和卡巴胆碱刺激的氨基比林（AP）积累的影响，并与分离的大鼠胃壁细胞中磷脂酶C/肌醇磷酸信号转导通路的细胞内变化进行了比较。
测定[14C]AP积累作为胃酸分泌的间接指标。在[3H]-肌醇预标记的大鼠胃壁细胞中，通过[3H]肌醇单磷酸释放来研究肌醇磷酸第二信使的激活情况。
低浓度5 nM的TPA使卡巴胆碱（0.1 mM）刺激的AP积累有小幅（45%）但显著的增加，更高浓度的TPA则剂量依赖性地抑制这种增加，同时卡巴胆碱刺激的AP积累的剂量反应曲线发生相应偏移。在所有研究浓度下，TPA均抑制dBcAMP（0.1 mM）刺激的AP摄取以及卡巴胆碱与dBcAMP共同诱导的协同刺激作用。在存在浓度不断增加的钙离子载体离子霉素（10(-8)-10(-5) M）的情况下，5 nM的TPA增加了AP积累（5 nM TPA时AP比值为4.02，无TPA时为1.23；P < 0.05），表明佛波酯刺激大鼠壁细胞摄取AP。同时研究[14C]AP积累和[3H]肌醇单磷酸释放表明，TPA对卡巴胆碱和卡巴胆碱加dBcAMP刺激的细胞的抑制作用是通过抑制受体/G蛋白/磷脂酶C相互作用介导的，导致肌醇磷酸释放减少。用dBcAMP、离子霉素和TPA（5 nM）共同刺激大鼠壁细胞并未重现卡巴胆碱与dBcAMP共同作用对AP积累的协同效应，这表明卡巴胆碱刺激的AP摄取似乎还通过一条独立于细胞内钙释放或蛋白激酶C激活的未知途径介导。
