MASS SPECTROMETRIC EVIDENCE AGENTS WHICH CAUSE CA2+ LOSS

用葡萄糖刺激胰岛诱导磷脂 非酯化花生四烯酸水解和积累， 可增强葡萄糖诱导的Ca 2+进入胰岛β细胞。的细胞 触发胰岛素分泌 Ca 2+损失？-细胞胞内 隔室已被提出诱导Ca 2+进入和事件 依赖于花生四烯酸代谢。 我们在这里研究的影响， 诱导细胞内螯合位点的Ca 2+损失， 离子载体A23187和毒胡萝卜素对花生四烯酸水解的影响 胰岛磷脂 A23187诱导胰岛功能下降 含花生四烯酸酯的磷脂和释放非酯化的 花生四烯酸 A23187诱导的花生四烯酸释放与A23187诱导的花生四烯酸释放相似。 当胰岛在Ca 2+充足或无Ca 2+的情况下受到刺激时的幅度 培养基或当胰岛负载细胞内Ca 2+螯合剂BAPTA时 A23187在无钙培养基中刺激， 不会导致？细胞胞浆[Ca 2 +]。 毒胡萝卜素还 在这些条件下诱导异花生四烯酸释放。 A23187-或 溴烯醇阻止毒胡萝卜素诱导的花生四烯酸释放 内酯（BEL）抑制剂，细胞磷脂酶A2（iPLA 2）， 催化活性不需要Ca 2+， 由钙调素调节并与钙调素物理相互作用， Ca 2+依赖机制。 导致胰岛Ca 2+丢失的药物 因此，细胞内区室诱导花生四烯酸水解， 磷脂通过BEL敏感机制，不需要 细胞质[Ca 2 +]升高，BEL敏感酶如iPLA 2或 相关的膜活性可能参与感受Ca ~（2+） 隔室内容物

Stimulation of pancreatic islets with glucose induces phospholipid hydrolysis and accumulation of nonesterified arachidonic acid, which may amplify the glucose-induced Ca2+ entry into islet ?-cells that triggers insulin secretion. Ca2+ loss from ?-cell intracellular compartments has been proposed to induce both Ca2+ entry and events dependent on arachidonate metabolism. We examine here effects of inducing Ca2+ loss from intracellular sequestration sites with ionophore A23187 and thapsigargin on arachidonate hydrolysis from islet phospholipids. A23187 induces a decline in islet arachidonate-containing phospholipids and release of nonesterified arachidonate. A23187-induced arachidonate release is of similar magnitude when islets are stimulated in Ca2+-replete or in Ca2+-free media or when islets loaded with the intracellular Ca2+ chelator BAPTA are stimulated in Ca2+-free medium, a condition in which A23187 induces no rise in ?-cell cytosolic [Ca2+]. Thapsigargin also induces i sletarachidonate release under these conditions. A23187-or thapsigargin-induced arachidonate release is prevented by a bromoenol lactone (BEL) inhibitor of a ?-cell phospholipase A2 (iPLA2) which does not require Ca2+ for catalytic activity and which is negatively modulated by and physically interacts with calmodulin by Ca2+-dependent mechanisms. Agents which cause Ca2+ loss from islet intracellular compartments thus induce arachidonate hydrolysis from phospholipids by a BEL-sensitive mechanism that does not require a rise in cytosolic [Ca2+], and a BEL-sensitive enzyme like iPLA2 or a related membranous activity may participate in sensing Ca2+ compartment content.