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Muthu Periasamy

Publications and source records attributed to Muthu Periasamy.

27 records · Page 2Linked to original sources
PubMed2003

Altered force-frequency response in non-failing hearts with decreased SERCA pump-level.

OBJECTIVE: Decreased SERCA2 activity is considered to significantly contribute to the contractile dysfunction of failing hearts. However, it is now known how decreases in SERCA activity affect cardiac function in detail and also if a decrease alone is sufficient to cause heart failure. METHODS: SERCA2 (+/-) gene-targeted mice (HET) were generated and heart function was analyzed using the isolated work-performing heart technique. Plasma and cardiac catecholamine levels were determined at three, six and nine months of age and heart sections from twelve months old mice subjected to standard histological analysis. RESULTS: We demonstrate that reduced expression of SERCA does not lead to cardiac hypertrophy or fibrosis and does not increase resting plasma-norepinephrine levels in HET mice. However, isolated perfused HET hearts exhibited decreased maximal rates of contraction and relaxation and prolonged time-parameters. The ability of the HET hearts to respond to increases in load (Starling) was not affected and they responded appropriately to beta-adrenergic stimulation. In contrast, the positive force-frequency response found in control hearts was not observed in the HET hearts. The response was flat and three out of five HET hearts failed to maintain work at 550 beats/min. CONCLUSIONS: We conclude that the SERCA2 pump level is a critical positive determinant of cardiac contractility and force-frequency relation.

Animals↗
PubMed2003

Differential vasoconstrictions induced by angiotensin II: role of AT1 and AT2 receptors in isolated C57BL/6J mouse blood vessels.

Genetically altered mice are increasingly used as experimental models. However, ANG II responses in mouse blood vessels have not been well defined. Therefore, the aim of this study was to determine the role of ANG II in regulating major blood vessels in C57/BL6J mice with isometric force measurements. Our results showed that in mouse abdominal aorta ANG II induced a concentration-dependent contraction (EC50 4.6 nM) with a maximum contraction of 75.1 +/- 4.9% at 100 nM compared with that of 60 mM K+. Similarly, femoral artery also exhibited a contractile response of 76.0 +/- 3.4% to the maximum concentration of ANG II (100 nM). In contrast, ANG II (100 nM)-induced contraction was significantly less in carotid artery (24.5 +/- 6.6%) and only minimal (3.5 +/- 0.31%) in thoracic aorta. The nitric oxide synthase inhibitor N omega-nitro-L-arginine methyl ester and the AT2 antagonist PD-123319 failed to enhance ANG II-induced contractions. However, an AT1 antagonist, losartan (10 microM), completely inhibited ANG II (100 nM) response in abdominal aorta and carotid artery. An AT1 agonist, [Sar1]-ANG II (100 nM), behaved similarly to ANG II (100 nM) in abdominal aorta and carotid artery. RT-PCR analyses showed that mouse thoracic aorta has a significantly lower AT1 mRNA level than abdominal aorta. These results demonstrate that major mouse vessels exhibit differential contractions to ANG II, possibly because of varied AT1 receptor levels.

Angiotensin II↗
PubMed2003

Calcium dynamics in the failing heart: restoration by beta-adrenergic receptor blockade.

Changes in calcium (Ca2+) regulation contribute to loss of contractile function in dilated cardiomyopathy. Clinical treatment using beta-adrenergic receptor antagonists (beta-blockers) slows deterioration of cardiac function in end-stage heart failure patients; however, the effects of beta-blocker treatment on Ca2+ dynamics in the failing heart are unknown. To address this issue, tropomodulin-overexpressing transgenic (TOT) mice, which suffer from dilated cardiomyopathy, were treated with a nonselective beta-receptor blocker (5 mg. kg-1. day-1 propranolol) for 2 wk. Ca2+ dynamics in isolated cardiomyocytes of TOT mice significantly improved after treatment compared with untreated TOT mice. Frequency-dependent diastolic and Ca2+ transient amplitudes were returned to normal in propranolol-treated TOT mice and but not in untreated TOT mice. Ca2+ kinetic measurements of time to peak and time decay of the caffeine-induced Ca2+ transient to 50% relaxation were also normalized. Immunoblot analysis of untreated TOT heart samples showed a 3.6-fold reduction of sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA), whereas Na+/Ca2+ exchanger (NCX) concentrations were increased 2.6-fold relative to nontransgenic samples. Propranolol treatment of TOT mice reversed the alterations in SERCA and NCX protein levels but not potassium channels. Although restoration of Ca2+ dynamics occurred within 2 wk of beta-blockade treatment, evidence of functional improvement in cardiac contractility assessed by echocardiography took 10 wk to materialize. These results demonstrate that beta-adrenergic blockade restores Ca2+ dynamics and normalizes expression of Ca2+-handling proteins, eventually leading to improved hemodynamic function in cardiomyopathic hearts.

Adrenergic beta-Antagonists↗
PubMed2003

The smooth muscle myosin seven amino acid heavy chain insert's kinetic role in the crossbridge cycle for mouse bladder.

The seven amino acid insert in the smooth muscle myosin heavy chain is thought to regulate the kinetics of contraction, contributing to the differences between fast and slow smooth muscle. The effects of this insert on force and stiffness were determined in bladder tissue of a transgenic mouse line expressing the insert SMB at one of three levels: an SMB wild type (+/+), an SMA homozygous type (-/-) and a heterozygous type (+/-). For skinned muscle, an increase in MgADP or inorganic phosphate (Pi) should shift the distribution of crossbridges in the actomyosin ATPase (AMATPase) to increase the relative population of the crossbridge state prior to ADP release and Pi release, respectively. Exogenous ADP increased force and stiffness in a manner consistent with increasing the Ca2+ concentration in both the +/+ and +/- mouse types. However, the -/- type showed a significantly greater increase in force than in stiffness suggesting that immediately prior to ADP release, the AMATPase either has an additional force producing isomerization state or a slower ADP dissociation rate for the -/- type compared to the +/+ or +/- types. Exogenous Pi led to a significantly greater decrease in stiffness than in force for all three mouse types suggesting that there is a force producing state prior to Pi release. In addition, the increase in Pi showed similar changes in the +/+ and -/- types whereas in the +/- type the decreases in both force and stiffness were greater than the other two mouse types indicating that the insert can affect the cooperativity between myosin heads. In conclusion, the seven amino acid insert modulates the kinetics and/or states of the AMATPase, which could lead to differences in the kinetics of contraction between fast and slow smooth muscle.

Adenosine Diphosphate↗
PubMed2003

Combined phospholamban ablation and SERCA1a overexpression result in a new hyperdynamic cardiac state.

OBJECTIVE: Phospholamban ablation or ectopic expression of SERCA1a in the heart results in significant increases in cardiac contractile parameters. The aim of the present study was to determine whether a combination of these two genetic manipulations may lead to further augmentation of cardiac function. METHODS: Transgenic mice with cardiac specific overexpression of SERCA1a were mated with phospholamban deficient mice to generate a model with SERCA1a overexpression in the phospholamban null background (SERCA1(OE)/PLB(KO)). The cardiac phenotype was characterized using quantitative immunoblotting, sarcoplasmic reticulum calcium uptake and single myocyte mechanics and calcium kinetics. RESULTS: Quantitative immunoblotting revealed an increase of 1.8-fold in total SERCA level, while SERCA2 was decreased to 50% of wild types. Isolated myocytes indicated increases in the maximal rates of contraction by 195 and 125%, the maximal rates of relaxation by 200 and 124%, while the time for 80% decay of the Ca(2+)-transient was decreased to 43 and 75%, in SERCA1(OE)/PLB(KO) hearts, compared to SERCA1a overexpressors and phospholamban knockouts, respectively. These mechanical alterations reflected parallel alterations in V(max) and EC(50) for Ca(2+) of the sarcoplasmic reticulum Ca(2+) transport system. Furthermore, there were no significant cardiac histological or pathological alterations, and the myocyte contractile parameters remained enhanced, up to 12 months of age. CONCLUSIONS: These findings suggest that a combination of SERCA1a overexpression and phospholamban ablation results in further enhancement of myocyte contractility over each individual alteration.

Animals↗
PubMed2003

Transcription factor Sp1 regulates SERCA2 gene expression in pressure-overloaded hearts: a study using in vivo direct gene transfer into living myocardium.

Pressure-overload hypertrophy results in downregulation of the sarcoplasmic reticulum Ca(2+)-ATPase pump encoding SERCA2 gene that regulates Ca(2+) uptake and myocardial relaxation. We previously characterized a proximal promoter region containing four Sp1 element consensus sequences (-284 to -72 base pairs (bp)) that was responsible for pressure-overload-induced transcriptional regulation. The purpose of the present study was to determine which of the Sp1 sites was responsible for the downregulation of SERCA2 gene transcription under pressure overload. Using an in vivo direct gene transfer assay, SERCA2 gene transcriptional activity was measured under pressure overload. Site-directed mutagenesis of the four Sp1 sites (I-IV) in the SERCA2 gene promoter (-284 to -72 bp) was performed. Wild-type and Sp1 mutant-luciferase reporter constructs were injected into the left-ventricular apices of pressure overload or sham-operated rats, and Sp1 mRNA and SERCA2 gene-luciferase activity was measured sequentially from 3 to 14 d after surgery. At 5 d, Sp1 mRNA in the pressure-overload rats increased to 124 +/- 7% of sham group levels, and pressure-overload-induced SERCA2 transcriptional activity was 15 +/- 4% of sham group when all four Sp1 sites remained intact. Mutation of the Sp1 mutant sites I (-196 to -191 bp) and III (-118 to -113 bp) blocked the inhibitory effect of pressure overload and resulted in SERCA2 gene transcriptional activity of 54 +/- 15% and 56 +/- 7% of sham group, respectively. We conclude that the pressure-overload-induced decrease in SERCA2 mRNA is mediated by Sp1 sites I and III.

Animals↗
PubMed2003

Physiological functions of plasma membrane and intracellular Ca2+ pumps revealed by analysis of null mutants.

It is known that plasma membrane Ca(2+)-transporting ATPases (PMCAs) extrude Ca(2+) from the cell and that sarco(endo)plasmic reticulum Ca(2+)-ATPases (SERCAs) and secretory pathway Ca(2+)-ATPases (SPCAs) sequester Ca(2+) in intracellular organelles; however, the specific physiological functions of individual isoforms are less well understood. This information is beginning to emerge from studies of mice and humans carrying null mutations in the corresponding genes. Mice with targeted or spontaneous mutations in plasma membrane Ca(2+)-ATPase isoform 2 (PMCA2) are profoundly deaf and have a balance defect due to the loss of PMCA2 in sensory hair cells of the inner ear. In humans, mutations in SERCA1 (ATP2A1) cause Brody disease, an impairment of skeletal muscle relaxation; loss of one copy of the SERCA2 (ATP2A2) gene causes Darier disease, a skin disorder; and loss of one copy of the SPCA1 (ATP2C1) gene causes Hailey-Hailey disease, another skin disorder. In the mouse, SERCA2 null mutants do not survive to birth, and heterozygous SERCA2 mutants have impaired cardiac performance and a high incidence of squamous cell cancers. SERCA3 null mutants survive and appear healthy, but endothelium-dependent relaxation of vascular smooth muscle is impaired and Ca(2+) signaling is altered in pancreatic beta cells. The diversity of phenotypes indicates that the various Ca(2+)-transporting ATPase isoforms serve very different physiological functions.

Amino Acid Sequence↗
PubMed2002

Altered dose response to beta-agonists in SERCA1a-expressing hearts ex vivo and in vivo.

In this study we evaluated the contractile characteristics of sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA)1a-expressing hearts ex vivo and in vivo and in particular their response to beta-adrenergic stimulation. Analysis of isolated, work-performing hearts revealed that transgenic (TG) hearts develop much higher maximal rates of contraction and relaxation than wild-type (WT) hearts. Addition of isoproterenol only moderately increased the maximal rate of relaxation (+20%) but did not increase contractility or decrease relaxation time in TG hearts. Perfusion with varied buffer Ca(2+) concentrations indicated an altered dose response to Ca(2+). In vivo TG hearts displayed fairly higher maximal rates of contraction (+ 25%) but unchanged relaxation parameters and a blunted but significant response to dobutamine. Our study also shows that the phospholamban (PLB) level was decreased (-40%) and its phosphorylation status modified in TG hearts. This study clearly demonstrates that increases in SERCA protein level alter the beta-adrenergic response and affect the phosphorylation of PLB. Interestingly, the overall cardiac function in the live animal is only slightly enhanced, suggesting that (neuro)hormonal regulations may play an important role in controlling in vivo heart function.

Adrenergic beta-Agonists↗