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Does the activity of ecto-5'-nucleotidase depend on the membrane potential?

ecto-5-核苷酸酶的活性是否取决于膜电位？

基本信息

批准号：
08877011
负责人：
ARITA Makoto
金额：
$ 1.15万
依托单位：
Oita Medical University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Exploratory Research
财政年份：
1996
资助国家：
日本
起止时间：
1996 至 1997
项目状态：
已结题

项目摘要

Under ischemia, adenosine is produced by enzymatic dephosphorylation of adenosine 5'-monophosphate (5'-AMP) by 5'-nucleotidase. We studied the effect of potassium ions on the production of adenosine, using flexibly mounted microdialysi techniques. The microdialysisi probe was implanted into the left ventricular myocardium of anesthetized open-chested rats, followed by a perfusion with Tyrode solution containing 5'-AMP.We clarified that the level of dialysate adenosine measured during continued supply of 5'-AMP reflects the activity of endogenous ecto-5'-nucleotidase. When the concentration of KCI in the Tyrode solution was increased stepwise from 5.4 mM (control) to up to 140 mM,the level of dialysate adenosine significantly increased, in a concentration-dependent manner and the latter effect was abolished in the presence of 1 mM CsCI,aK^+ channel inhibitor. Equivalent increases in osmotic concentration of the Tyrode solution, made by adding sucrose (270 mM) , did not affect the dialys … More ate adenosine concentration. In isolated guinea pig ventricular papillary muscles, the blockers of inward rectifier K^+ current (I_<K1>), i.e., CsCI and BaCI_2 (20mM) depolarized the resting membrane potential significantly. To rule out the possibility that the enhanced production of adenosine by high concentration of KCI is caused by the release of noradrenaline, secondary to the depolarization of sympathetic nerve terminals, we repeated the same experiments in the presence of 30 muM prazocin, an alpha^1-blocker. Even under this condition, introduction of 140 mM KC1 containing solution significantly enhanced the adenosine production, thereby dismissing the possibility of adenosine production mediated by noradrenaline-induced, alpha_1-receptor-mediated activation of protein kinase C activity.These results suggest that increases in extracellular K^+ concentration depolarizes the resting membrane potential of cardiomyocytes and increase the activity of ecto-5'-nucleotidase with eventual increases of adenosine production in in situ rat's hearts. Less

在局部缺血时，腺苷通过5 '-核苷酸酶对腺苷5'-单磷酸（5 '-AMP）的酶促去磷酸化而产生。我们研究了钾离子对腺苷生产的影响，使用灵活的安装微透析技术。将微透析探针植入麻醉开胸大鼠的左心室心肌，然后用含5 ′-AMP的台氏液灌流，我们阐明了在持续供应5 ′-AMP期间所测的透析液腺苷水平反映了内源性外5 ′-核苷酸酶的活性。当台氏液中KCl的浓度从5.4 mM（对照）逐步增加到140 mM时，透析液中腺苷的水平以浓度依赖性方式显著增加，并且在1 mM CsCl（钾通道抑制剂）存在下，后者的作用被消除。通过加入蔗糖（270 mM）使台氏溶液的渗透浓度等效增加，并不影响透析液的透析率。 ...更多信息腺苷浓度。在离体豚鼠心室乳头肌中，内向整流K^+电流（I_）的阻断剂<K1>，CsCl和BaCl_2（20 mM）使静息膜电位显著去极化。为了排除高浓度KCl引起腺苷生成增加是由交感神经末梢去极化后释放去甲肾上腺素引起的可能性，我们在存在30 μ M哌唑星（一种α ^1受体阻滞剂）的情况下重复了同样的实验。即使在这种条件下，引入含有140 mM KCl的溶液也显著增强了腺苷的产生，从而排除了由去甲肾上腺素诱导的腺苷产生介导的可能性，这些结果表明，细胞外K^+浓度的增加使心肌细胞静息膜电位去极化，并增加细胞外-5 '-核苷酸酶与最终增加腺苷生产在原位大鼠心脏。少