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Syed J Khundmiri - One of the best experts on this subject based on the ideXlab platform.
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aldosterone regulates na k atpase activity in human renal proximal tubule cells through mineralocorticoid receptor
Biochimica et Biophysica Acta, 2013Co-Authors: Sarah A Salyer, Jason Parks, Michelle T Barati, Eleanor D Lederer, Barbara J Clark, Janet D Klein, Syed J KhundmiriAbstract:The mechanisms by which aldosterone increases Na(+), K(+) ATPase and sodium channel activity in cortical collecting duct and distal nephron have been extensively studied. Recent investigations demonstrate that aldosterone increases Na-H exchanger-3 (NHE-3) activity, bicarbonate transport, and H(+) ATPase in proximal tubules. However, the role of aldosterone in regulation of Na(+), K(+) ATPase in proximal tubules is unknown. We hypothesize that aldosterone increases Na(+), K(+) ATPase activity in proximal tubules through activation of the mineralocorticoid receptor (MR). Immunohistochemistry of kidney sections from human, rat, and mouse kidneys revealed that the MR is expressed in the cytosol of tubules staining positively for Lotus tetragonolobus agglutinin and type IIa sodium-phosphate cotransporter (NpT2a), confirming proximal tubule localization. Adrenalectomy in Sprague-Dawley rats decreased expression of MR, ENaC α, Na(+), K(+) ATPase α1, and NHE-1 in all tubules, while supplementation with aldosterone restored expression of above proteins. In human kidney proximal tubule (HKC11) cells, treatment with aldosterone resulted in translocation of MR to the nucleus and phosphorylation of SGK-1. Treatment with aldosterone also increased Na(+), K(+) ATPase-mediated (86)Rb uptake and expression of Na(+), K(+) ATPase α1 subunits in HKC11 cells. The effects of aldosterone on Na(+), K(+) ATPase-mediated (86)Rb uptake were prevented by spironolactone, a competitive inhibitor of aldosterone for the MR, and partially by Mifepristone, a glucocorticoid receptor (GR) inhibitor. These results suggest that aldosterone regulates Na(+), K(+) ATPase in renal proximal tubule cells through an MR-dependent mechanism.
Ole M. Sejersted - One of the best experts on this subject based on the ideXlab platform.
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bridging integrator 1 bin1 initiates t tubule growth during cardiac development and disease
Biophysical Journal, 2015Co-Authors: David B Lipsett, Michael Frisk, William Marszalec, Ole M. Sejersted, Jan Magnus Aronsen, Neha SinghAbstract:The cardiomyocyte T-Tubule network is malleable; T-Tubules develop after birth and are disrupted during diseases such as heart failure (HF). In failing cells, loss of the primarily transverse orientation of tubules is accompanied by growth of longitudinal T-Tubules (LTTs), which we have shown are compensatory. We presently hypothesized that bridging integrator 1 (BIN1), a membrane tubulating protein, triggers T-Tubule growth during both development and disease. Confocal microscopy and di-8-ANEPPS staining revealed cardiomyocytes isolated from 10 day-old mice predominantly contained LTTs, whereas the mature transverse network began developing 10-15 days following birth. Additionally, we observed that cardiac BIN1 protein levels in mice were highest during periods of T-Tubule biogenesis, suggesting that BIN1 may be involved during early stages of development. In rats examined 6 weeks following myocardial infarction, appearance of LTTs was accompanied by a 2-fold increase in BIN1 transcript levels, despite marked loss of transverse elements. Immunostaining of failing cardiomyocytes fixed in 4% paraformaldehyde confirmed the presence of BIN1 in newly formed LTTs. To directly examine whether BIN1 upregulation could underlie the observed appearance of LTTs in developing and diseased cardiomyocytes, we expressed BIN1 in cultured cardiomyocytes lacking T-Tubules (HL-1 cells). Following transfection with exogenous BIN1, a dense network of BIN1-positive sarcolemmal membrane invaginations was formed in HL-1 cells as early as 12 hours after transfection. Importantly, these tubules were chaotically organized and resembled the LTTs grown prior to T-Tubule maturation. Labeling of intracellular Ca2+ with fluo-4 revealed that these tubules have T-Tubule-like functionality, as Ca2+ release events occurred adjacent to BIN1-positive tubules. We propose that BIN1 initiates LTT growth during development and disease, and that upregulation of BIN1 in the diseased heart may represent a return to an immature gene program.
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bridging integrator 1 bin1 induced t tubule formation in cardiomyocytes
Biophysical Journal, 2014Co-Authors: David B Lipsett, Michael Frisk, Ole M. Sejersted, Jan Magnus Aronsen, Neha Singh, Ivar SjaastadAbstract:The T-Tubule system is a branching network of membrane invaginations essential for efficient Ca2+-induced Ca2+ release in myocytes. Significant remodeling of this system has been observed during heart failure (HF), resulting in delayed Ca2+ release at sites lacking T-Tubules. Despite its considerable role in HF aetiology, the signaling mechanisms behind T-Tubule remodeling remain largely unknown. Bridging integrator 1 (BIN1) has recently drawn considerable interest due to its altered expression during HF and ability to tubulate membranes. In rats examined 6 weeks following myocardial infarction, BIN1 transcription was significantly elevated in animals with compensated or end-stage HF, compared to SHAM operated controls. Although overall T-Tubule density was unchanged, confocal imaging of isolated cells stained with di-8-ANEPPS confirmed that the transverse pattern of T-Tubules was lost in failing cardiomyocytes, as indicated by reduced peak power in fast Fourier transforms. Interestingly, between-peak power was increased, consistent with the increased fraction of longitudinal tubules visible in failing cardiomyocytes. The role of BIN1 in T-Tubule growth was investigated using HL-1 cells, a differentiated murine cardiac cell line lacking both intrinsic BIN1 and T-Tubules. When transfected with hBIN1, HL-1 cells developed BIN1-positive invaginations as early as 12 hours following transfection. Whereas BIN1 transcript and protein levels rapidly rose to a peak 24 hours following transfection, BIN1-generated tubules gradually increased in density up until 48 hours after transfection. Additionally, early Ca2+ release at sites containing BIN1-positive tubules indicated that these structures improve Ca2+ release synchrony across the cell. We propose that BIN1 is a crucial regulator of T-Tubule development in both healthy and failing cardiomyocytes. In the setting of heart failure, increased BIN1 expression may promote growth of longitudinal tubules that compensate for loss of transverse elements, thereby improving calcium homeostasis in this disease.
David B Lipsett - One of the best experts on this subject based on the ideXlab platform.
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bridging integrator 1 bin1 initiates t tubule growth during cardiac development and disease
Biophysical Journal, 2015Co-Authors: David B Lipsett, Michael Frisk, William Marszalec, Ole M. Sejersted, Jan Magnus Aronsen, Neha SinghAbstract:The cardiomyocyte T-Tubule network is malleable; T-Tubules develop after birth and are disrupted during diseases such as heart failure (HF). In failing cells, loss of the primarily transverse orientation of tubules is accompanied by growth of longitudinal T-Tubules (LTTs), which we have shown are compensatory. We presently hypothesized that bridging integrator 1 (BIN1), a membrane tubulating protein, triggers T-Tubule growth during both development and disease. Confocal microscopy and di-8-ANEPPS staining revealed cardiomyocytes isolated from 10 day-old mice predominantly contained LTTs, whereas the mature transverse network began developing 10-15 days following birth. Additionally, we observed that cardiac BIN1 protein levels in mice were highest during periods of T-Tubule biogenesis, suggesting that BIN1 may be involved during early stages of development. In rats examined 6 weeks following myocardial infarction, appearance of LTTs was accompanied by a 2-fold increase in BIN1 transcript levels, despite marked loss of transverse elements. Immunostaining of failing cardiomyocytes fixed in 4% paraformaldehyde confirmed the presence of BIN1 in newly formed LTTs. To directly examine whether BIN1 upregulation could underlie the observed appearance of LTTs in developing and diseased cardiomyocytes, we expressed BIN1 in cultured cardiomyocytes lacking T-Tubules (HL-1 cells). Following transfection with exogenous BIN1, a dense network of BIN1-positive sarcolemmal membrane invaginations was formed in HL-1 cells as early as 12 hours after transfection. Importantly, these tubules were chaotically organized and resembled the LTTs grown prior to T-Tubule maturation. Labeling of intracellular Ca2+ with fluo-4 revealed that these tubules have T-Tubule-like functionality, as Ca2+ release events occurred adjacent to BIN1-positive tubules. We propose that BIN1 initiates LTT growth during development and disease, and that upregulation of BIN1 in the diseased heart may represent a return to an immature gene program.
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bridging integrator 1 bin1 induced t tubule formation in cardiomyocytes
Biophysical Journal, 2014Co-Authors: David B Lipsett, Michael Frisk, Ole M. Sejersted, Jan Magnus Aronsen, Neha Singh, Ivar SjaastadAbstract:The T-Tubule system is a branching network of membrane invaginations essential for efficient Ca2+-induced Ca2+ release in myocytes. Significant remodeling of this system has been observed during heart failure (HF), resulting in delayed Ca2+ release at sites lacking T-Tubules. Despite its considerable role in HF aetiology, the signaling mechanisms behind T-Tubule remodeling remain largely unknown. Bridging integrator 1 (BIN1) has recently drawn considerable interest due to its altered expression during HF and ability to tubulate membranes. In rats examined 6 weeks following myocardial infarction, BIN1 transcription was significantly elevated in animals with compensated or end-stage HF, compared to SHAM operated controls. Although overall T-Tubule density was unchanged, confocal imaging of isolated cells stained with di-8-ANEPPS confirmed that the transverse pattern of T-Tubules was lost in failing cardiomyocytes, as indicated by reduced peak power in fast Fourier transforms. Interestingly, between-peak power was increased, consistent with the increased fraction of longitudinal tubules visible in failing cardiomyocytes. The role of BIN1 in T-Tubule growth was investigated using HL-1 cells, a differentiated murine cardiac cell line lacking both intrinsic BIN1 and T-Tubules. When transfected with hBIN1, HL-1 cells developed BIN1-positive invaginations as early as 12 hours following transfection. Whereas BIN1 transcript and protein levels rapidly rose to a peak 24 hours following transfection, BIN1-generated tubules gradually increased in density up until 48 hours after transfection. Additionally, early Ca2+ release at sites containing BIN1-positive tubules indicated that these structures improve Ca2+ release synchrony across the cell. We propose that BIN1 is a crucial regulator of T-Tubule development in both healthy and failing cardiomyocytes. In the setting of heart failure, increased BIN1 expression may promote growth of longitudinal tubules that compensate for loss of transverse elements, thereby improving calcium homeostasis in this disease.
A W Trafford - One of the best experts on this subject based on the ideXlab platform.
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physiology and patho physiology of the cardiac transverse tubular system
Current Opinion in Physiology, 2018Co-Authors: Charlotte E R Smith, Jessica L Caldwell, A W Trafford, Katharine M DibbAbstract:Cardiac transverse (t)-tubules play a vital role in ensuring synchronous contraction. They contain L-type Ca2+ channels which closely couple with intracellular Ca2+ release channels throughout the cell to mediate a rapid and uniform Ca2+ release. The complexity of the T-Tubule network varies between species and across cardiac chambers. In addition, T-Tubule networks are also highly labile with density increasing during development and decreasing in disease. Recent work using super-resolution and 3D electron microscopy has shown that T-Tubules themselves are highly diverse structures with the proteins located on and around them differentially modulated compared to other sites within the cell. This review will summarise our current understanding of the T-Tubule network in health and disease with focus on T-Tubule heterogeneity, the importance of T-Tubules in excitation–contraction coupling and the proteins responsible for T-Tubule regulation.
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171 amphiphysin ii bin1 driven transverse tubule formation in cardiac muscle
Heart, 2017Co-Authors: Jessica L Caldwell, Rebecca F Taylor, D A Eisner, K M Dibb, A W TraffordAbstract:Transverse (t)-tubules are vital for maintaining normal contractility of the heart through the tight regulation of excitation coupling. In cardiac disease, such as heart failure, T-Tubule loss is closely associated with decreased synchrony of calcium release from the sarcoplasmic reticulum, resulting in impaired contractility. Thus, determining the mechanisms that control T-Tubule formation is essential for understanding cardiac disease. Evidence suggests that the protein Amphiphysin II (AmpII) controls T-Tubule formation in cardiac muscle and thus, may play a vital role in calcium regulation. Several studies, including our own, have shown that gene silencing of AmpII causes T-Tubule loss in both skeletal and cardiac muscle. Furthermore, in non-muscle cells that usually lack T-Tubules, expression of some variants of AmpII led to tubule formation. We therefore aimed to extend these observations and determine if AmpII is sufficient to drive T-Tubule formation in the heart. Neonate rat ventricular myocytes (NRVMs) were isolated from 2 day old rats and maintained in culture. Vectors encoding isoforms 5, 8 and 9 of the AmpII gene (Bin1) with a C-terminal mKate2 fluorescent protein tag were transiently expressed in NRVMs using FuGENE 6 lipofection. A vector containing the mKate2 fluorescent tag only was used as negative control. After 48 hours, over-expression of Bin1 was confirmed at both the mRNA and protein level. Tubule formation was assessed using the membrane dye FM-464 and confocal microscopy. Of cells successfully transfected with Bin1, 95% had developed tubule structures. Conversely, tubules were absent in cells only expressing the fluorescent tag (p To determine if Bin1 driven tubules are functional, transfected cells were loaded with the Ca2+ indicator Fluo-8 AM and field stimulated. When compared with untransfected myocytes, expression of Bin1 isoforms 5, 8 and 9 increased the amplitude of the systolic calcium transient (p Over-expression of Bin1 isoforms 5, 8 and 9 led to the formation of tubular structures in NRVMs. Whilst Bin1 isoforms 8 appears to play more of a role in tubule formation in NRVMs, these data suggest that other Bin1 isoforms (5 and 9) may enhance calcium kinetics. These data therefore suggest that Bin1 plays a vital role in tubule formation and development in cardiac myocytes. Given the importance of T-Tubules to normal excitation contraction coupling and their perturbation in heart failure we therefore suggest that Bin1 might be a novel therapeutic target.
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dependence of cardiac transverse tubules on the bar domain protein amphiphysin ii bin 1
Circulation Research, 2014Co-Authors: Jessica L Caldwell, Rebecca F Taylor, D A Eisner, Charlotte E R Smith, Katharine M Dibb, Ashraf Kitmitto, A W TraffordAbstract:Rationale: Transverse tubules (T-Tubules) regulate cardiac excitation–contraction coupling and exhibit interchamber and interspecies differences in expression. In cardiac disease, T-Tubule loss occurs and affects the systolic calcium transient. However, the mechanisms controlling T-Tubule maintenance and whether these factors differ between species, cardiac chambers, and in a disease setting remain unclear. Objective: To determine the role of the Bin/Amphiphysin/Rvs domain protein amphiphysin II (AmpII) in regulating T-Tubule maintenance and the systolic calcium transient. Methods and Results: T-Tubule density was assessed by di-4-ANEPPS, FM4-64 or WGA staining using confocal microscopy. In rat, ferret, and sheep hearts T-Tubule density and AmpII protein levels were lower in the atrium than in the ventricle. Heart failure (HF) was induced in sheep using right ventricular tachypacing and ferrets by ascending aortic coarctation. In both HF models, AmpII protein and T-Tubule density were decreased in the ventricles. In the sheep, atrial T-Tubules were also lost in HF and AmpII levels decreased. Conversely, junctophilin 2 levels did not show interchamber differences in the rat and ferret nor did they change in HF in the sheep or ferret. In addition, in rat atrial and sheep HF atrial cells where T-Tubules were absent, junctophilin 2 had sarcomeric intracellular distribution. Small interfering RNA–induced knockdown of AmpII protein reduced T-Tubule density, calcium transient amplitude, and the synchrony of the systolic calcium transient. Conclusions: AmpII is intricately involved in T-Tubule maintenance. Reducing AmpII protein decreases T-Tubule density, reduces the amplitude, and increases the heterogeneity of the systolic calcium transient.
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characterization of an extensive transverse tubular network in sheep atrial myocytes and its depletion in heart failure
Circulation-heart Failure, 2009Co-Authors: Katharine M Dibb, D A Eisner, Jessica D Clarke, Margaux A Horn, Mark A Richards, Helen K Graham, A W TraffordAbstract:Background— In ventricular myocytes, the majority of structures that couple excitation to the systolic rise of Ca2+ are located at the transverse tubular (T-Tubule) membrane. In the failing ventricle, disorganization of T-Tubules disrupts excitation contraction coupling. The T-Tubule membrane is virtually absent in the atria of small mammals resulting in spatiotemporally distinct profiles of intracellular Ca2+ release on stimulation in atrial and ventricular cells. The aims of this study were to determine (i) whether atrial myocytes from a large mammal (sheep) possess T-Tubules, (ii) whether these are functionally important, and (iii) whether they are disrupted in heart failure. Methods and Results— Sheep left atrial myocytes were stained with di-4-ANEPPS. Nearly all control cells had an extensive T-Tubule network resulting in each voxel in the cell being nearer to a membrane (sarcolemma or T-Tubule) than would otherwise be the case. T-Tubules decrease the distance of 50% of voxels from a membrane from 3....
Jan Magnus Aronsen - One of the best experts on this subject based on the ideXlab platform.
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bridging integrator 1 bin1 initiates t tubule growth during cardiac development and disease
Biophysical Journal, 2015Co-Authors: David B Lipsett, Michael Frisk, William Marszalec, Ole M. Sejersted, Jan Magnus Aronsen, Neha SinghAbstract:The cardiomyocyte T-Tubule network is malleable; T-Tubules develop after birth and are disrupted during diseases such as heart failure (HF). In failing cells, loss of the primarily transverse orientation of tubules is accompanied by growth of longitudinal T-Tubules (LTTs), which we have shown are compensatory. We presently hypothesized that bridging integrator 1 (BIN1), a membrane tubulating protein, triggers T-Tubule growth during both development and disease. Confocal microscopy and di-8-ANEPPS staining revealed cardiomyocytes isolated from 10 day-old mice predominantly contained LTTs, whereas the mature transverse network began developing 10-15 days following birth. Additionally, we observed that cardiac BIN1 protein levels in mice were highest during periods of T-Tubule biogenesis, suggesting that BIN1 may be involved during early stages of development. In rats examined 6 weeks following myocardial infarction, appearance of LTTs was accompanied by a 2-fold increase in BIN1 transcript levels, despite marked loss of transverse elements. Immunostaining of failing cardiomyocytes fixed in 4% paraformaldehyde confirmed the presence of BIN1 in newly formed LTTs. To directly examine whether BIN1 upregulation could underlie the observed appearance of LTTs in developing and diseased cardiomyocytes, we expressed BIN1 in cultured cardiomyocytes lacking T-Tubules (HL-1 cells). Following transfection with exogenous BIN1, a dense network of BIN1-positive sarcolemmal membrane invaginations was formed in HL-1 cells as early as 12 hours after transfection. Importantly, these tubules were chaotically organized and resembled the LTTs grown prior to T-Tubule maturation. Labeling of intracellular Ca2+ with fluo-4 revealed that these tubules have T-Tubule-like functionality, as Ca2+ release events occurred adjacent to BIN1-positive tubules. We propose that BIN1 initiates LTT growth during development and disease, and that upregulation of BIN1 in the diseased heart may represent a return to an immature gene program.
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bridging integrator 1 bin1 induced t tubule formation in cardiomyocytes
Biophysical Journal, 2014Co-Authors: David B Lipsett, Michael Frisk, Ole M. Sejersted, Jan Magnus Aronsen, Neha Singh, Ivar SjaastadAbstract:The T-Tubule system is a branching network of membrane invaginations essential for efficient Ca2+-induced Ca2+ release in myocytes. Significant remodeling of this system has been observed during heart failure (HF), resulting in delayed Ca2+ release at sites lacking T-Tubules. Despite its considerable role in HF aetiology, the signaling mechanisms behind T-Tubule remodeling remain largely unknown. Bridging integrator 1 (BIN1) has recently drawn considerable interest due to its altered expression during HF and ability to tubulate membranes. In rats examined 6 weeks following myocardial infarction, BIN1 transcription was significantly elevated in animals with compensated or end-stage HF, compared to SHAM operated controls. Although overall T-Tubule density was unchanged, confocal imaging of isolated cells stained with di-8-ANEPPS confirmed that the transverse pattern of T-Tubules was lost in failing cardiomyocytes, as indicated by reduced peak power in fast Fourier transforms. Interestingly, between-peak power was increased, consistent with the increased fraction of longitudinal tubules visible in failing cardiomyocytes. The role of BIN1 in T-Tubule growth was investigated using HL-1 cells, a differentiated murine cardiac cell line lacking both intrinsic BIN1 and T-Tubules. When transfected with hBIN1, HL-1 cells developed BIN1-positive invaginations as early as 12 hours following transfection. Whereas BIN1 transcript and protein levels rapidly rose to a peak 24 hours following transfection, BIN1-generated tubules gradually increased in density up until 48 hours after transfection. Additionally, early Ca2+ release at sites containing BIN1-positive tubules indicated that these structures improve Ca2+ release synchrony across the cell. We propose that BIN1 is a crucial regulator of T-Tubule development in both healthy and failing cardiomyocytes. In the setting of heart failure, increased BIN1 expression may promote growth of longitudinal tubules that compensate for loss of transverse elements, thereby improving calcium homeostasis in this disease.
