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首页> 外文期刊>Biochemistry >BIDIRECTIONAL ACTIVITY OF THE ENDOPLASMIC RETICULUM CA2+-ATPASE OF BOVINE ADRENAL CORTEX
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BIDIRECTIONAL ACTIVITY OF THE ENDOPLASMIC RETICULUM CA2+-ATPASE OF BOVINE ADRENAL CORTEX

机译：牛肾上腺皮质内膜网CA2 + -ATPase的双向活性

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摘要

It is generally accepted that the ryanodine receptor and the inositol 1,4,5-trisphosphate receptor play major roles in the complex mechanisms by which agonists increase intracellular Ca2+ concentration. In these mechanisms, the endoplasmic reticulum Ca2+-ATPase has been attributed an accessory role of refilling the intracellular Ca2+ store. In the present study, the activity of the microsomal Ca2+-ATPase of bovine adrenal cortex was investigated. We show that the Ca2+-pumping activity of the Ca2+-ATPase is related to the ADP/ATP ratio. Our results also show that a brisk increase of the ADP/ATP ratio upon addition of exogenous ADP triggered a rapid release of Ca2+ from preloaded microsomes. ADP released Ca2+ in a dose-dependent manner with an EC(50) of 2.98 +/- 0.78 mM. ADP-induced Ca2+ release was not prevented by heparin, ruling out the participation of the inositol 1,4,5-trisphosphate receptor. ADP-induced Ca2+ release could not be attributed to the mere inhibition of the Ca2+-ATPase, since the rate of ADP-induced Ca2+ release was 20 times faster than the rate of Ca2+ release induced by a maximal concentration of thapsigargin (2 mu M). ADP-induced Ca2+ release experiments performed in the presence of [P-32]PO4 revealed a concomitant production of [P-32]ATP. ADP-induced [P-32]ATP production was dose-dependent, with an EC(50) of 5.50 +/- 0.70 mM, ADP-induced [P-32]ATP production was prevented by ionomycin (10 mu M) and by high concentrations of extramicrosomal Ca2+. These results demonstrate that the microsomal Ca2+-ATPase of adrenal cortex possesses a bidirectional activity that depends on ADP concentrations, the Ca2+ gradient across the microsomal membrane, and probably also ATP concentrations. The reverse activity of the endoplasmic reticulum Ca2+-ATPase could therefore play an additional role in cellular Ca2+ homeostasis. Indeed, under physiological or pathological conditions, where local ADP concentrations are increasing (and/or ATP concentrations are decreasing), the reverse activity of the Ca2+ pump should liberate Ca2+ from intracellular stores.
机译：人们普遍认为，在激动剂增加细胞内Ca2 +浓度的复杂机制中，ryanodine受体和1,4,5-三磷酸肌醇受体起主要作用。在这些机制中，内质网Ca2 + -ATPase被认为是补充细胞内Ca2 +储存的辅助作用。在本研究中，研究了牛肾上腺皮质微粒体Ca2 + -ATPase的活性。我们表明，Ca2 + -ATPase的Ca2 +泵送活性与ADP / ATP比率有关。我们的结果还表明，添加外源ADP后，ADP / ATP比率迅速增加，导致Ca2 +从预载微粒体中快速释放。 ADP以剂量依赖性方式释放Ca2 +，其EC（50）为2.98 +/- 0.78 mM。肝素不能阻止ADP诱导的Ca2 +释放，排除了肌醇1,4,5-三磷酸受体的参与。 ADP诱导的Ca2 +释放不能仅仅归因于Ca2 + -ATPase的抑制，因为ADP诱导的Ca2 +释放速率比最大浓度的毒胡萝卜素（2μM）诱导的Ca2 +释放速率快20倍。 。在[P-32] PO4存在下进行的ADP诱导的Ca2 +释放实验表明，会同时产生[P-32] ATP。 ADP诱导的[P-32] ATP产生是剂量依赖性的，EC（50）为5.50 +/- 0.70 mM，离子霉素（10μM）和高浓度的超微粒体Ca2 +。这些结果表明，肾上腺皮质的微粒体Ca2 + -ATPase具有双向活性，该活性取决于ADP浓度，微粒体膜上的Ca2 +梯度以及ATP浓度。内质网Ca2 + -ATPase的反向活性因此可以在细胞Ca2 +稳态中发挥额外作用。实际上，在生理或病理条件下，局部ADP浓度在增加（和/或ATP浓度在降低），Ca2 +泵的反向活性应将Ca2 +从细胞内储存中释放出来。

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