Murthy K S, Makhlouf G M
Department of Medicine, Medical College of Virginia, Richmond 23298-0711.
Am J Physiol. 1991 Dec;261(6 Pt 1):G945-51. doi: 10.1152/ajpgi.1991.261.6.G945.
The pattern of inositol phospholipid metabolism in response to stimulation by contractile agonists was examined in muscle cells isolated separately from circular and longitudinal muscle layers of guinea pig intestine. Addition of cholecystokinin octapeptide (CCK-8) to circular muscle cells caused a prompt decrease in phosphatidylinositol 4,5-bisphosphate (PtdInsP2) (50 +/- 6%) and PtdInsP (38 +/- 9%), which reached a nadir in 15 s. Addition of CCK-8 to longitudinal muscle cells caused a decrease in PtdInsP only (42 +/- 6%); PtdInsP2 levels, which were three times lower in this cell type, did not change throughout the period of stimulation. Hydrolysis of PtdInsP2 in circular muscle cells was accompanied by a concentration-dependent increase in inositol 1,4,5-trisphosphate [Ins(1,4,5)P3]; the maximal increase was 10 to 16 times greater in circular muscle cells as measured by radioreceptor assay and by ion-exchange chromatography. The small amounts of InsP3 produced in longitudinal muscle cells did not result from more rapid degradation, since the rates of disappearance of exogenous Ins(1,4,5)P3 in both cell types were similar. Within 5 s after addition of CCK-8, InsP3 comprised 73 +/- 5% of total inositol phosphates produced in circular muscle cells and 2.0 +/- 0.2% in longitudinal muscle cells. These divergent patterns indicate that inositol phospholipid metabolism is channeled toward generation of InsP3 in circular muscle cells only; the metabolic pattern in these cells parallels the selective presence of high-affinity InsP3 receptors and the pattern of intracellular Ca2+ mobilization.
在分别从豚鼠肠道环形肌层和纵行肌层分离出的肌肉细胞中，研究了收缩激动剂刺激下肌醇磷脂代谢的模式。向环形肌细胞中添加八肽胆囊收缩素（CCK-8）会导致磷脂酰肌醇4,5-二磷酸（PtdInsP2）迅速减少（50±6%）和磷脂酰肌醇磷酸（PtdInsP）减少（38±9%），在15秒时达到最低点。向纵行肌细胞中添加CCK-8仅导致PtdInsP减少（42±6%）；在这种细胞类型中PtdInsP2水平低三倍，在整个刺激期间没有变化。环形肌细胞中PtdInsP2的水解伴随着1,4,5-三磷酸肌醇[Ins(1,4,5)P3]浓度依赖性增加；通过放射受体测定和离子交换色谱法测量，环形肌细胞中的最大增加量比纵行肌细胞大10至16倍。纵行肌细胞中产生的少量InsP3并非来自更快的降解，因为两种细胞类型中外源Ins(1,4,5)P3的消失速率相似。添加CCK-8后5秒内，InsP3在环形肌细胞中产生的总肌醇磷酸中占73±5%，在纵行肌细胞中占2.0±0.2%。这些不同的模式表明，肌醇磷脂代谢仅在环形肌细胞中导向InsP3的生成；这些细胞中的代谢模式与高亲和力InsP3受体的选择性存在以及细胞内Ca2+动员模式平行。
