Krishnamurthi S, Joseph S, Kakkar V V
Biochem J. 1986 Aug 15;238(1):193-9. doi: 10.1042/bj2380193.
Previous studies have demonstrated an inhibition of agonist-induced inositol phospholipid breakdown and intracellular Ca2+ ([Ca2+]i) mobilization by phorbol esters in platelets. In this study, we have examined the effect of phorbol 12-myristate 13-acetate (PMA) on agonist-induced granule secretion and correlated it with agonist-induced [Ca2+]i mobilization, arachidonate and thromboxane (Tx) release in human platelets. With increasing times of incubation with PMA (10 s-5 min), the rise in [Ca2+]i induced by thrombin and the TxA2 mimetic, U46619, was increasingly inhibited (90-100% with 5 min incubation) and, correlating with this, thrombin-induced [3H]arachidonate, TxB2 and beta-thromboglobulin (beta TG) release were also inhibited. In addition, the conversion of exogenously added arachidonate to TxB2 was inhibited (50-80%) by a 10 s-5 min pretreatment with PMA. However, secretion of 5-hydroxy[14C]tryptamine (5HT) induced by thrombin or U46619 was not inhibited by 10 s-2 min incubations with PMA and, on the contrary, with low agonist concentrations, was potentiated by PMA in the absence of a significant rise in [Ca2+]i or endogenous Tx formation, to levels significantly greater than or equal to the sum of that obtained when agonist and PMA were added separately. With longer times of incubation with PMA (5 min), these synergistic effects became less pronounced as inhibitory effects of PMA on agonist-induced [14C]5HT secretion became apparent. The results indicate that, while PMA may cause an inhibition of agonist-induced [Ca2+]i mobilization resulting in an inhibition of agonist-induced arachidonate, TxB2 and beta TG release, its effects on agonist-induced 5HT secretion may be complicated by [Ca2+]i-independent synergistic effects of agonist and PMA.
先前的研究已证明佛波酯对血小板中激动剂诱导的肌醇磷脂分解和细胞内Ca2+（[Ca2+]i）动员具有抑制作用。在本研究中，我们检测了佛波酯12-肉豆蔻酸酯13-乙酸酯（PMA）对激动剂诱导的人血小板颗粒分泌的影响，并将其与激动剂诱导的[Ca2+]i动员、花生四烯酸和血栓素（Tx）释放相关联。随着与PMA孵育时间的增加（10秒至5分钟），凝血酶和TxA2模拟物U46619诱导的[Ca2+]i升高受到越来越强的抑制（孵育5分钟时抑制率达90 - 100%），与此相关，凝血酶诱导的[3H]花生四烯酸、TxB2和β-血小板球蛋白（βTG）释放也受到抑制。此外，用PMA预处理10秒至5分钟可抑制外源性添加的花生四烯酸向TxB2的转化（50 - 80%）。然而，凝血酶或U46619诱导的5-羟色胺（5HT）分泌在与PMA孵育10秒至2分钟时未受抑制，相反，在激动剂浓度较低时，PMA在[Ca2+]i无显著升高或内源性Tx形成的情况下增强了5HT分泌，使其水平显著高于或等于分别添加激动剂和PMA时获得的总和。随着与PMA孵育时间延长（5分钟），随着PMA对激动剂诱导的[14C]5HT分泌的抑制作用变得明显，这些协同作用变得不那么显著。结果表明，虽然PMA可能会抑制激动剂诱导的[Ca2+]i动员，从而抑制激动剂诱导的花生四烯酸、TxB2和βTG释放，但其对激动剂诱导的5HT分泌的影响可能因激动剂和PMA的[Ca2+]i非依赖性协同作用而变得复杂。
