Ohlmann P, Leray C, Ravanat C, Hallia A, Cassel D, Cazenave J P, Gachet C
INSERM U.311, Biologie et Pharmacologie des Interactions du Sang avec les Vaisseaux et les Biomatériaux, Etablissement de Transfusion Sanguine, 10 rue Spielmann, B.P. no 36, F-67065 Strasbourg Cédex, France.
Biochem J. 1998 Apr 15;331 ( Pt 2)(Pt 2):431-6. doi: 10.1042/bj3310431.
Human platelet CD38 is a multifunctional ectoenzyme catalysing the synthesis and hydrolysis of cADP-ribose (cADPR), a recently identified calcium-mobilizing agent that acts independently of D-myo-inositol 1,4,5-trisphosphate and is known to be expressed by human platelets. The present work shows that ADP-ribosyl cyclase activity is exclusively a membrane activity, of which the major part is located in plasma membranes and a small part in internal membranes. In broken cells, cyclase activity was insensitive to the presence of calcium and was not modulated by agonists such as thrombin or ADP, whereas in intact cells thrombin increased cADPR formation by 30%, an effect due to fusion of granules with the plasma membrane. In order to assess the role of cADPR as a calcium-mobilizing agent, vesicles were prepared from internal membranes and loaded with 45CaCl2. These vesicles were efficiently discharged by IP3 in a dose-dependent manner, but were not responsive to cADPR or ryanodine in the presence or absence of calmodulin. Thus cADPR is unlikely to play a role in intracellular calcium release in human blood platelets.
人血小板CD38是一种多功能胞外酶，可催化cADP - 核糖（cADPR）的合成与水解，cADPR是一种最近发现的钙动员剂，其作用独立于D - 肌醇1,4,5 - 三磷酸，已知在人血小板中表达。目前的研究表明，ADP - 核糖基环化酶活性完全是一种膜活性，其中大部分位于质膜，一小部分位于内膜。在破碎细胞中，环化酶活性对钙的存在不敏感，也不受凝血酶或ADP等激动剂的调节，而在完整细胞中，凝血酶使cADPR形成增加30%，这是由于颗粒与质膜融合所致。为了评估cADPR作为钙动员剂的作用，从内膜制备了囊泡并装载了45CaCl2。这些囊泡在有或没有钙调蛋白的情况下，均能被IP3以剂量依赖性方式有效释放，但对cADPR或ryanodine无反应。因此，cADPR不太可能在人血小板的细胞内钙释放中发挥作用。
