兔虹膜平滑肌中乙酰胆碱刺激的磷脂酰肌醇4,5-二磷酸磷酸二酯酶裂解对钙离子的需求

Requirement for calcium ions in acetylcholine-stimulated phosphodiesteratic cleavage of phosphatidyl-myo-inositol 4,5-bisphosphate in rabbit iris smooth muscle.

作者信息

Akhtar R A, Abdel-Latif A A

出版信息

Biochem J. 1980 Dec 15;192(3):783-91. doi: 10.1042/bj1920783.

DOI:10.1042/bj1920783

PMID:6263262

原文链接:https://pmc.ncbi.nlm.nih.gov/articles/PMC1162401/

Abstract

The mechanism of acetylcholine-stimulated breakdown of phosphatidyl-myo-inositol 4,5-bisphosphate and its dependence on extracellular Ca(2+) was investigated in the rabbit iris smooth muscle. 2. Acetylcholine (50mum) increased the breakdown of phosphatidylinositol bisphosphate in [(3)H]inositol-labelled muscle by 28% and the labelling of phosphatidylinositol by 24% of that of the control. Under the same experimental conditions there was a 33 and 48% increase in the production of (3)H-labelled inositol trisphosphate and inositol monophosphate respectively. Similarly carbamoylcholine and ionophore A23187 increased the production of these water-soluble inositol phosphates. Little change was observed in the (3)H radioactivity of inositol bisphosphate. 3. Both inositol trisphosphatase and inositol monophosphatase were demonstrated in subcellular fractions of this tissue and the specific activity of the former was severalfold higher than that of the latter. 4. The acetylcholine-stimulated production of inositol trisphosphate and inositol monophosphate was inhibited by atropine (20mum), but not tubocurarine (100mum); and it was abolished by depletion of extracellular Ca(2+) with EGTA, but restored on addition of low concentrations of Ca(2+) (20mum). 5. Calcium-antagonistic agents, such as verapamil (20mum), dibenamine (20mum) or La(3+) (2mm), also abolished the production of the water-soluble inositol phosphates in response to acetylcholine. 6. Release of inositol trisphosphate from exogenous phosphatidylinositol bisphosphate by iris muscle microsomal fraction (;microsomes') was stimulated by 43% in the presence of 50mum-Ca(2+). 7. The results indicate that increased Ca(2+) influx into the iris smooth muscle by acetylcholine and ionophore A23187 markedly activates phosphatidylinositol bisphosphate phosphodiesterase and subsequently increases the production of inositol trisphosphate and its hydrolytic product inositol monophosphate. The marked increase observed in the production of inositol monophosphate could also result from Ca(2+) activation of phosphatidylinositol phosphodiesterase. However, there was no concomitant decrease in the (3)H radioactivity of this phospholipid.

摘要

在兔虹膜平滑肌中研究了乙酰胆碱刺激的磷脂酰肌醇4,5 - 二磷酸分解机制及其对细胞外Ca(2+)的依赖性。2. 乙酰胆碱（50μM）使[（3）H]肌醇标记的肌肉中磷脂酰肌醇二磷酸的分解增加28%，磷脂酰肌醇的标记量增加到对照的24%。在相同实验条件下，（3）H标记的肌醇三磷酸和肌醇单磷酸的产生分别增加33%和48%。同样，氨甲酰胆碱和离子载体A23187也增加了这些水溶性肌醇磷酸的产生。肌醇二磷酸的（3）H放射性变化不大。3. 在该组织的亚细胞组分中证实了肌醇三磷酸酶和肌醇单磷酸酶，前者的比活性比后者高几倍。4. 乙酰胆碱刺激的肌醇三磷酸和肌醇单磷酸的产生受到阿托品（20μM）的抑制，但不受筒箭毒碱（100μM）的抑制；用EGTA耗尽细胞外Ca(2+)可使其消除，但加入低浓度的Ca(2+)（20μM）后可恢复。5. 钙拮抗剂，如维拉帕米（20μM）、二苯胺（20μM）或La(3+)（2mM），也可消除乙酰胆碱刺激引起的水溶性肌醇磷酸的产生。6. 在50μM - Ca(2+)存在下，虹膜肌肉微粒体组分（微粒体）从外源性磷脂酰肌醇二磷酸释放肌醇三磷酸的量增加了43%。7. 结果表明，乙酰胆碱和离子载体A23187使Ca(2+)流入虹膜平滑肌增加，显著激活磷脂酰肌醇二磷酸磷酸二酯酶，随后增加肌醇三磷酸及其水解产物肌醇单磷酸的产生。肌醇单磷酸产生的显著增加也可能是Ca(2+)激活磷脂酰肌醇磷酸二酯酶的结果。然而，这种磷脂的（3）H放射性并没有相应降低。