The Ca2+ extrusion function of the four mammalian isoforms of the plasma membrane calcium ATPases (PMCAs) is well established. There is also ever-increasing detail known of their roles in global and local Ca2+ homeostasis and intracellular Ca2+ signaling in a wide variety of cell types and tissues. It is becoming clear that the spatiotemporal patterns of expression of the PMCAs and the fact that their abundances and relative expression levels vary from cell type to cell type both reflect and impact on their specific functions in these cells. Over recent years it has become increasingly apparent that these genes have potentially significant roles in human health and disease, with PMCAs1-4 being associated with cardiovascular diseases, deafness, autism, ataxia, adenoma, and malarial resistance. This review will bring together evidence of the variety of tissue-specific functions of PMCAs and will highlight the roles these genes play in regulating normal physiological functions and the considerable impact the genes have on human disease.

The heart responds to pathological overload through myocyte hypertrophy. Here we show that this response is regulated by cardiac fibroblasts via a paracrine mechanism involving plasma membrane calcium ATPase 4 (PMCA4). Pmca4 deletion in mice, both systemically and specifically in fibroblasts, reduces the hypertrophic response to pressure overload; however, knocking out Pmca4 specifically in cardiomyocytes does not produce this effect. Mechanistically, cardiac fibroblasts lacking PMCA4 produce higher levels of secreted frizzled related protein 2 (sFRP2), which inhibits the hypertrophic response in neighbouring cardiomyocytes. Furthermore, we show that treatment with the PMCA4 inhibitor aurintricarboxylic acid (ATA) inhibits and reverses cardiac hypertrophy induced by pressure overload in mice. Our results reveal that PMCA4 regulates the development of cardiac hypertrophy and provide proof of principle for a therapeutic approach to treat this condition.

Background and PurposeThe Hippo pathway has emerged as a potential therapeutic target to control pathological cardiac remodelling. The core components of the Hippo pathway, mammalian Ste‐20 like kinase 1 (Mst1) and mammalian Ste‐20 like kinase 2 (Mst2), modulate cardiac hypertrophy, apoptosis, and fibrosis. Here, we study the effects of pharmacological inhibition of Mst1/2 using a novel inhibitor XMU‐MP‐1 in controlling the adverse effects of pressure overload‐induced hypertrophy.Experimental ApproachWe used cultured neonatal rat cardiomyocytes (NRCM) and C57Bl/6 mice with transverse aortic constriction (TAC) as in vitro and in vivo models, respectively, to test the effects of XMU‐MP‐1 treatment. We used luciferase reporter assays, western blots and immunofluorescence assays in vitro, with echocardiography, qRT‐PCR and immunohistochemical methods in vivo.Key ResultsXMU‐MP‐1 treatment significantly increased activity of the Hippo pathway effector yes‐associated protein and inhibited phenylephrine‐induced hypertrophy in NRCM. XMU‐MP‐1 improved cardiomyocyte survival and reduced apoptosis following oxidative stress. In vivo, mice 3 weeks after TAC, were treated with XMU‐MP‐1 (1 mg·kg−1) every alternate day for 10 further days. XMU‐MP‐1‐treated mice showed better cardiac contractility than vehicle‐treated mice. Cardiomyocyte cross‐sectional size and expression of the hypertrophic marker, brain natriuretic peptide, were reduced in XMU‐MP‐1‐treated mice. Improved heart function in XMU‐MP‐1‐treated mice with TAC, was accompanied by fewer TUNEL positive cardiomyocytes and lower levels of fibrosis, suggesting inhibition of cardiomyocyte apoptosis and decreased fibrosis.Conclusions and ImplicationsThe Hippo pathway inhibitor, XMU‐MP‐1, reduced cellular hypertrophy and improved survival in cultured cardiomyocytes and, in vivo, preserved cardiac function following pressure overload.

Objective-Effects on platelet aggregation of adenosine triphosphate (ATP) released from damaged cells and from platelets undergoing exocytosis have not been clearly established. In this study we report on the effects of ATP on platelet aggregation in whole blood. Methods and Results-Aggregation, measured using a platelet-counting technique, occurred in response to ATP and was maximal at 10 to 100 mol/L. It was abolished by MRS2179, AR-C69931, and creatine phosphate/creatine phosphokinase, implying that conversion to adenosine diphosphate (ADP) is required. ATP did not induce aggregation in platelet-rich plasma, but aggregation did occur when apyrase or hexokinase was added. Aggregation also occurred after addition of leukocytes to platelet-rich plasma (as a source of ecto-ATPase), and this was potentiated on removal of adenosine by adenosine deaminase, indicating that adenosine production modulates the response. Dipyridamole, which inhibits adenosine uptake into erythrocytes, inhibited aggregation induced by ATP in whole blood, and adenosine deaminase reversed this. DN9693 and forskolin synergized with dipyridamole to inhibit ATP-induced aggregation. 4 The released ADP can interact with P2Y 1 and P2Y 12 (formally known as P 2T ) receptors on platelets and induce platelet aggregation, 5-7 which contributes to normal hemostasis and to thrombus formation. However, the effect of the released ATP is unclear. It is known that ATP can interact with P2X 1 receptors on platelets, causing a transient Ca 2ϩ mobilization, 8,9 but this does not result in platelet aggregation, and the importance of P2X 1 receptors to overall platelet function is unknown. It is also known that ATP acts as an antagonist of the effects of ADP at P2Y 1 and P2Y 12 receptors 10,11 and that high concentrations can inhibit ADP-induced platelet aggregation. 12 When considering the possible effects of ATP on platelets in vitro and in vivo, the presence of enzymes present on blood cells and endothelial cells and in plasma that metabolize ATP must be taken into account. These include enzymes that convert ATP to ADP and ADP to AMP (NTPDase-1, also known as ATP diphosphohydrolase, CD 39 and EC 3.6.1.5), 13,14 ATP to AMP and ADP to AMP (5Ј-monophosphate phosphoanhydrolase/phosphodiesterase, NMPP), 15 and AMP to adenosine (5Ј-nucleotidase), 13 the latter being an inhibitor of platelet aggregation. 10,16 Also, adenosine can be taken up and neutralized by erythrocytes and other blood cells, thus limiting its potential inhibitory action. 17,18 Thus, the overall effect of ATP could depend on several competing influences. Conclusions-ATPIn this study, we have investigated the effects of ATP on platelet aggregation in whole blood and in platelet-rich plasma (PRP). We used hirudin as the anticoagulant to ensure that the conditions used were as near physiological as possible. We found that ATP induces platelet aggregation in whole blood but not in PRP, and we have investigated the mechanisms that are involved. Methods MaterialsHirudin (recombinant desulphato-hirudi...