The plasma membrane calcium ATPase modulates calcium homeostasis, intracellular signaling events and function in platelets

Abstract

ATPase modulates calcium homeostasis, intracellular signaling events and function in platelets. J Thromb Haemost 2010; 8: 2766-74.Summary. Background: The plasma membrane calcium ATPase (PMCA) regulates localized signaling events in a variety of cell types, although its functional role in platelets remains undefined. Objectives: To investigate the role of PMCA in determining platelet intracellular calcium concentration ([Ca 2+ ] i ) at rest and following agonist stimulation, and to define the corresponding effects upon different stages of platelet activation. Methods: [Ca 2+ ] i was continuously measured in Fura-2-loaded platelets and in vitro and in vivo functional analyses performed in the presence of the PMCA inhibitor carboxyeosin (CE). Results: Concentrations of CE that selectively inhibited Ca 2+ extrusion through PMCA were established in human platelets. [Ca 2+ ] i was elevated by CE in resting platelets, although collagen-stimulated Ca 2+ release was reduced. Impaired Ca 2+ mobilization upon agonist stimulation was accompanied by reduced dense granule secretion and impaired platelet aggregation. Platelet aggregation responses were also reduced in PMCA4 )/) mice and in an in vivo mouse model of platelet thromboembolism. Conversely, inhibition of PMCA promoted the early and later stages of platelet activation, observed as enhanced adhesion to fibrinogen, and accelerated clot retraction. Investigations into the signaling mechanisms underlying CE-mediated inhibition of platelet aggregation implicated cGMP-independent vasodilator-stimulated phosphoprotein phosphorylation. Conclusions: Disruption of PMCA activity perturbs platelet Ca 2+ homeostasis and function in a time-dependent manner, demonstrating that PMCA differentially regulates Ca 2+ -dependent signaling events, and hence function, throughout the platelet activation process.

The Plasma Membrane Calcium ATPasesand Their Role as Major New Players in Human Disease

“…Studies have found that PMCA4 is recruited to the cytoskeleton during platelet activation through an interaction with the LIM family protein CLP36 to facilitate clot formation (39). The critical role of the PMCA during aggregation has been highlighted by studies using platelets from PMCA4 knockout mice, which display impaired platelet aggregation when stimulated with collagen (174). Similar results were obtained upon incubation of platelets with the PMCA inhibitor carboxyeosin, which led to elevated resting Ca 2ϩ , but smaller increases in Ca 2ϩ upon stimulation alongside reduced aggregation (174).…”

Pericellular Ca2+recycling potentiates thrombin-evoked Ca2+signals in human platelets

“…Similarly, it has recently been reported that blocking the platelet plasma membrane Ca 2+ ‐ATPase (PMCA) inhibited agonist‐evoked Ca 2+ signaling as well as dense granule secretion (Jones et al. ). Together these results suggest that Ca 2+ removal across the platelet plasma membrane is required for fast dense granule secretion and thus the full development of agonist‐evoked Ca 2+ signals.…”

“…; Jy and Haynes ) and inhibitors of the plasma membrane Ca 2+ ‐ATPase (Jones et al. ). We therefore hypothesized that Ca 2+ exported across the plasma membrane by the NCX may recycle back into the cytosol via Ca 2+ ‐permeable ion channels.…”

Ca2+ signalling in cardiovascular disease: the role of the plasma membrane calcium pumps

“…The expression of PMCA2 is much more specific, being localised to inner ear cilia, Purkinje cells and the mammary gland [22][23][24][25][26]. PMCA3 is also expressed in the brain as well as skeletal muscle cells and pancreatic islet cells [22,[27][28][29], whilst PMCA4 is expressed in a wide range of cell types including erythrocytes, platelets, spermatozoa, heart, vascular smooth muscle, kidney, skeletal muscle, stomach, intestine and brain [21,22,[30][31][32][33][34][35].…”

“…PMCA2 knockout mice, as well as spontaneous mouse mutants of PMCA2, exhibit both deafness and ataxia [44][45][46]. Deletion of PMCA4 leads to sperm immotility and subsequent infertility [21,35] and alterations in aspects of platelet function including aggregation [32] suggesting that although PMCA4 is essentially ubiquitously expressed in the adult mouse its function is highly specialised.…”