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Background idiopathic dilated cardiomyopathy (DCM) is recognised to be a heritable disorder, yet clinical genetic testing does not produce a diagnosis in >50% of paediatric patients. identifying a genetic cause is crucial because this knowledge can affect management options, cardiac surveillance in relatives and reproductive decision-making. in this study, we sought to identify the underlying genetic defect in a patient born to consanguineous parents with rapidly progressive DCM that led to death in early infancy. Methods and results exome sequencing revealed a potentially pathogenic, homozygous missense variant, c.542g>t, p.(gly181Val), in SOD2. this gene encodes superoxide dismutase 2 (SOD2) or manganesesuperoxide dismutase, a mitochondrial matrix protein that scavenges oxygen radicals produced by oxidationreduction and electron transport reactions occurring in mitochondria via conversion of superoxide anion (O2-•) into H2O2. Measurement of hydroethidine oxidation showed a significant increase in O2-• levels in the patient's skin fibroblasts, as compared with controls, and this was paralleled by reduced catalytic activity of SOD2 in patient fibroblasts and muscle. lentiviral complementation experiments demonstrated that mitochondrial SOD2 activity could be completely restored on transduction with wild type SOD2. Conclusion Our results provide evidence that defective SOD2 may lead to toxic increases in the levels of damaging oxygen radicals in the neonatal heart, which can result in rapidly developing heart failure and death. We propose SOD2 as a novel nuclear-encoded mitochondrial protein involved in severe human neonatal cardiomyopathy, thus expanding the wide range of genetic factors involved in paediatric cardiomyopathies. [ABSTRACT FROM AUTHOR]

[Na.sup.+],[K.sup.+]-ATPase and gastric [H.sup.+],[K.sup.+]-ATPase are two related enzymes that are responsible for active cation transport. [Na.sup.+],[K.sup.+]-ATPase activity is inhibited specifically by ouabain, whereas [H.sup.+],[K.sup.+]-ATPase is insensitive to this drug. Because it is not known which parts of the catalytic subunit of [Na.sup.+],[K.sup.+]-ATPase are responsible for ouabain binding, we prepared chimeras in which small parts of the [Alpha]-subunit of [H.sup.+],[K.sup.+]-ATPase were replaced by their counterparts of the [[Alpha].sub.1]-subunit of rat [Na.sup.+],[K.sup.+]-ATPase. A chimeric enzyme in which transmembrane segments 5 and 6 of [H.sup.+],[K.sup.+]-ATPase were replaced by those of [Na.sup.+],[K.sup.+]-ATPase could form a phosphorylated intermediate, but hardly showed a [K.sup.+]-stimulated dephosphorylation reaction. When transmembrane segments 3 and 4 of [Na.sup.+],[K.sup.+]-ATPase were also included in this chimeric ATPase, [K.sup.+]-stimulated dephosphorylation became apparent. This suggests that there is a direct interaction between the hairpins M3-M4 and M5-M6. Remarkably, this chimeric enzyme, HN34/56, had obtained a high-affinity ouabain-binding site, whereas the rat [Na.sup.+],[K.sup.+]-ATPase, from which the hairpins originate, has a low affinity for ouabain. The low affinity of the rat [Na.sup.+],[K.sup.+]-ATPase previously had been attributed to the presence of two charged amino acids in the extracellular domain between M1 and M2. In the HN34/56 chimera, the M1/M2 loop, however, originates from [H.sup.+],[K.sup.+]-ATPase, which has two polar uncharged amino acids on this position. Placement of two charged amino acids in the M1/M2 loop of chimera HN34/56 results in a decreased ouabain affinity. This indicates that although the M1/M2 loop affects the ouabain affinity, binding occurs when the M3/M4 and M5/M6 hairpins of [Na.sup.+],[K.sup.+]-ATPase are present.

Hoenderop, Joost G. J., Peter H. G. M. Willems, and Rene J. M. Bindels. Toward a comprehensive molecular model of active calcium reabsorption. Am. J. Physiol. Renal Physiol. 278: F352-F360, 2000.--The fine tuning of [Ca.sup.2+] excretion in the kidney takes place in the distal nephron, which consists of the distal convoluted tubule, connecting tubule, and initial portion of the cortical collecting duct. In these segments, [Ca.sup.2+] is reabsorbed through an active transcellular pathway. The apical influx of [Ca.sup.2+] into the distal renal cell is presumably the rate-limiting step in this process, and its molecular identity has remained obscure so far. The recently discovered epithelial [Ca.sup.2+] channel (ECaC) exhibits the expected properties for being the gatekeeper in transcellular [Ca.sup.2+] reabsorption. The characteristics and potential physiological role of ECaC will be discussed in this review. Our knowledge of the mechanisms involved in the regulation of transcellular [Ca.sup.2+] transport has advanced rapidly since the development of cell models originating from distal tubular cells. Studies using these models indicate that hormones including arginine vasopressin, [PGE.sub.2], adenosine, ATP, and atrial natriuretic peptide should be considered as calciotropic hormones controlling renal [Ca.sup.2+] handling. Evidence is now beginning to emerge that the stimulating calciotropic hormones utilize new cAMP-independent pathways to stimulate [Ca.sup.2+] reabsorption. These new findings allow the development of a comprehensive and detailed model of the process of transcellular calcium transport in the kidney whereby the individual contribution of the participating transporters can now be fully appreciated. calcium channel; parathyroid hormone; vitamin [D.sub.3]; atrial natriuretic peptide; arginine vasopressin; hypercalciuria; guanosine 3'5'-cyclic monophosphate; adenosine 3'5'-cyclic monophosphate

Van Baal, Jurgen, Joost G. J. Hoenderop, Maarten Groenendijk, Carel H. Van Os, Rene J. M. Bindels, and Peter H. G. M. Willems. Hormone-stimulated [Ca.sup.2+] transport in rabbit kidney: multiple sites of inhibition by exogenous ATP. Am. J. Physiol. 277 (Renal Physiol. 46): F899-F906, 1999.--Exogenous ATP markedly reduced 1-desamino-8-D-arginine vasopressin (dDAVP)-stimulated [Ca.sup.2+] transport and cAMP accumulation in primary cultures of rabbit connecting tubule and cortical collecting duct cells. Similarly, ATP inhibited the stimulatory effect of 8-bromo-cAMP. At first sight, this is in agreement with the 'classic' concept that dDAVP exerts its stimulatory effect via cAMP. However, dDAVP-stimulated [Ca.sup.2+] transport was markedly reduced by the protein kinase C (PKC) inhibitor chelerythrine, reported previously to inhibit the cAMP-independent pathway responsible for parathyroid hormone-, [[Arg.sup.8]]vasopressin-, [PGE.sub.2-], and adenosine-stimulated [Ca.sup.2+] transport. Chelerythrine also inhibited the increase in [Ca.sup.2+] transport evoked by the cAMP-independent [A.sub.1] receptor agonist [N.sup.6]-cyclopentyladenosine (CPA). Downregulation of phorbol ester-sensitive PKC isoforms by chronic phorbol ester treatment has been shown before to be without effect on hormone-stimulated [Ca.sup.2+] transport, indicating that the chelerythrine-inhibitable pathway consists of a phorbol ester-insensitive PKC isoform. Here, this maneuver did not affect ATP inhibition of dDAVP-stimulated [Ca.sup.2+] transport and cAMP formation, while abolishing ATP inhibition of CPA-stimulated [Ca.sup.2+] transport. These findings show that ATP acts via 1) a phorbol ester-sensitive PKC isoform to inhibit hormonal stimulation of [Ca.sup.2+] transport at the level of the chelerythrine-inhibitable pathway involving a phorbol ester-insensitive PKC isoform and 2) a phorbol ester-insensitive mechanism to inhibit [V.sub.2] receptor-mediated concomitant activation of this pathway and adenylyl cyclase. connecting tubule; cortical collecting duct; adenosine 5'-triphosphate; protein kinase C; calcium transport

Mitochondria play a central role in cellular energy production, and their dysfunction can trigger a compensatory increase in glycolytic flux to sustain cellular ATP levels. Here, we studied the mechanism of this homeostatic phenomenon in C2C12 myoblasts. Acute (30 min) mitoenergetic dysfunction induced by the mitochondrial inhibitors piericidin A and antimycin A stimulated Glut1-mediated glucose uptake without altering Glut1 (also known as SLC2A1) mRNA or plasma membrane levels. The serine/threonine liver kinase B1 (LKB1; also known as STK11) and AMP-activated protein kinase (AMPK) played a central role in this stimulation. In contrast, ataxiatelangiectasia mutated (ATM; a potential AMPK kinase) and hydroethidium (HEt)-oxidizing reactive oxygen species (ROS; increased in piericidin-A- and antimycin-A-treated cells) appeared not to be involved in the stimulation of glucose uptake. Treatment with mitochondrial inhibitors increased NAD+ and NADH levels (associated with a lower NAD+:NADH ratio) but did not affect the level of Glut1 acetylation. Stimulation of glucose uptake was greatly reduced by chemical inhibition of Sirt2 or mTOR--RAPTOR. We propose that mitochondrial dysfunction triggers LKB1-mediated AMPK activation, which stimulates Sirt2 phosphorylation, leading to activation of mTOR--RAPTOR and Glut1-mediated glucose uptake. [ABSTRACT FROM AUTHOR]