Effects of carbachol and pancreozymin (cholecystokinin-octapeptide) on polyphosphoinositide metabolism in the rat pancreas in vitro.
Effects of carbachol and pancreozymin (cholecystokinin-octapeptide) on polyphosphoinositide metabolism in the rat pancreas in vitro.
复制标题
卡巴胆碱和胰酶（胆囊收缩素八肽）对体外大鼠胰腺多磷酸肌醇代谢的影响。
作者：
J. Orchard;J. Davis;R. Larson;R. Farese
我们研究了磷脂酰肌醇4，5-二磷酸[PtdIns（4，5）P2]的水解可能是在卡巴胆碱和胰酶素（八肽胆囊收缩素）作用期间大鼠胰腺中[32 P]Pi掺入磷脂酸（PtdA）和磷脂酰肌醇（PtdIns）增加的起始事件的可能性。预标记腺泡2 h后，[32 P]Pi掺入PtdA、PtdIns（4，5）P2和磷脂酰肌醇4-磷酸（PtdIns 4P）的量达到平衡。随后添加卡巴胆碱或胰酶素导致PtdIns（4，5）P2中的32 P在10-15秒内减少30-50%，随后PtdA和PtdIns中的[32 P]Pi掺入量连续增加。PtdIns 4P的32 P-标记的类似变化没有一致地观察到。色谱纯化的PtdIns（4，5）P2中32 P的减少反映了该物质的实际减少，这一事实提供了以下证实：（a）当PtdIns（4，5）P2用[2- 3 H]肌醇预标记时，和（B）当PtdIns（4，5）P2用[2- 3 H]肌醇预标记时，5）P2在甲醇碱水解和离子交换色谱后作为其特异性产物（甘油磷酸肌醇二磷酸）测量。促分泌素诱导的PtdIns（4，5）P2的分解不受Ca 2+缺乏的抑制（严重到足以抑制淀粉酶分泌和PtdIns的Ca 2+依赖性水解），并且离子载体A23187处理不引起PtdIns（4，5）P2水解。在剂量反应研究中，在相同浓度的卡巴胆碱下，PtdIns（4，5）P2的水解增加和[32 P]Pi掺入PtdA的增加开始。我们的研究结果表明，PtdIns（4，5）P2的水解是胰腺促分泌素动员Ca 2+作用的早期事件，并且这种水解可能启动PtdA和PtdIns的Ca 2+非依赖性标记。Ca 2+动员可能遵循这些反应，并随后导致PtdIns的Ca 2+依赖性水解和胞吐作用。
We studied the possibility that hydrolysis of phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2] may be the initiating event for the increase in [32P]Pi incorporation into phosphatidic acid (PtdA) and phosphatidylinositol (PtdIns) during carbachol and pancreozymin (cholecystokinin-octapeptide) action in the rat pancreas. After prelabelling acini for 2h, [32P]Pi incorporation into PtdA, PtdIns(4,5)P2 and phosphatidylinositol 4-phosphate (PtdIns4P) had reached equilibrium. Subsequent addition of carbachol or pancreozymin caused 32P in PtdIns(4,5)P2 to decrease by 30-50% within 10-15 s, and this was followed by sequential increases in [32P]Pi incorporation into PtdA and PtdIns. Similar changes in 32P-labelling of PtdIns4P were not consistently observed. Confirmation that the decrease in 32P in chromatographically-purified PtdIns(4,5)P2 reflected an actual decrease in this substance was provided by the fact that similar results were obtained (a) when PtdIns(4,5)P2 was prelabelled with [2-3H]inositol, and (b) when PtdIns(4,5)P2 was measured as its specific product (glycerophosphoinositol bisphosphate) after methanolic alkaline hydrolysis and ion-exchange chromatography. The secretogogue-induced breakdown of PtdIns(4,5)P2 was not inhibited by Ca2+ deficiency (severe enough to inhibit amylase secretion and Ca2+-dependent hydrolysis of PtdIns), and ionophore A23187 treatment did not provoke PtdIns(4,5)P2 hydrolysis. The increase in the hydrolysis of PtdIns(4,5)P2 and the increase in [32P]Pi incorporation into PtdA commenced at the same concentration of carbachol in dose-response studies. Our findings suggest that the hydrolysis of PtdIns(4,5)P2 is an early event in the action of pancreatic secretogogues that mobilize Ca2+, and it is possible that this hydrolysis may initiate the Ca2+-independent labelling of PtdA and PtdIns. Ca2+ mobilization may follow these responses, and subsequently cause Ca2+-dependent hydrolysis of PtdIns and exocytosis.