Calmodulin Regulates Thromboxane and Prostacyclin Biosynthesis and Metabolism

Abstract

Calmodulin, a low molecular weight (16,700 dalton), heat-stable acidic protein, has been identified and isolated from a wide variety of tissues [1]. The protein displays multi-functions, controlling the activities of cyclic nucleotide phosphodiesterase [2, 3], adenylate cyclase [4, 5], Ca²⁺-ATPase [6, 7], myosin light chain kinase [8, 9], NAD kinase [10], phosphorylase kinase [11], and quanylate cyclase [12]. In addition, it regulates Ca²⁺ transport in erythrocytes and sarcoplasmic reticulum [13], phosphorylation of membrane proteins [14],and disassembly of microtubules [15]. Recently we have presented preliminary evidence suggesting that the stimulation of phospholipase A2, by Ca²⁺ in human blood platelet is mediated through calmodulin [16]. Phospholipase A2, controls the intracellular level of arachidonic acid, which is rate-limiting for the synthesis of thromboxane A2, a potent inducer of platelet aggregation and release reaction [17]. Thus, calmodulin may play an important role in platelet function.