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Biomedical subjects

N S Dhalla

Publications and source records attributed to N S Dhalla.

At least 37 records · Page 2Linked to original sources
PubMed2000

Attenuation of changes in sarcoplasmic reticular gene expression in cardiac hypertrophy by propranolol and verapamil.

The effects of propranolol and verapamil on contractile dysfunction, subcellular remodeling and changes in gene expression in cardiac hypertrophy due to pressure overload were examined. Rats were subjected to banding of the abdominal aorta and then treated with either propranolol (10 mg/kg daily), verapamil (5 mg/kg daily) or vehicle for 8 weeks after the surgery. Depression of the left ventricular function in the hypertrophied heart was associated with decreases in myofibrillar and myosin Ca2+ ATPase activities as well as Ca2+-pump and Ca2+-release activities of the sarcoplasmic reticulum (SR). The level of alpha-myosin heavy chain (alpha-MHC) mRNA was decreased while that of beta-MHC mRNA was increased in the pressure-overloaded heart. The level of SR Ca2+-pump ATPase (SERCA2) mRNA and protein content for SERCA2 were decreased in the pressure overloaded heart. Treatment of the hypertrophied animals with propranolol or verapamil resulted in preservation of the left ventricular function and prevention of the subcellular alterations. Shift in the alpha- and beta-MHC mRNA levels and changes in the expression in SERCA2 mRNA level and protein content were also attenuated by these treatments. The results suggest that blockade of beta-adrenoceptors or voltage-dependent calcium channels normalizes the cardiac gene expression, prevents subcellular remodeling and thus attenuates heart dysfunction in rats with cardiac hypertrophy. Furthermore, both cardiac beta-adrenoceptors and L-type Ca2+-channels may be involved in the genesis of cardiac hypertrophy due to pressure overload.

Adenosine Triphosphatases↗
PubMed2000

Modification of beta-adrenoceptor signal transduction pathway by genetic manipulation and heart failure.

The beta-adrenoceptor (beta-AR) mediated signal transduction pathway in cardiomyocytes is known to involve beta1- and beta2-ARs, stimulatory (Gs) and inhibitory (Gi) guanine nucleotide binding proteins, adenylyl cyclase (AC) and cAMP-dependent protein kinase (PKA). The activation of beta1- and beta2-ARs has been shown to increase heart function by increasing Ca2+ -movements across the sarcolemmal membrane and sarcoplasmic reticulum through the stimulation of Gs-proteins, activation of AC and PKA enzymes and phosphorylation of the target sites. The activation of PKA has also been reported to increase phosphorylation of some myofibrillar proteins (for promoting cardiac relaxation) and nuclear proteins (for cardiac hypertrophy). The activation of beta2-AR has also been shown to affect Gi-proteins, stimulate mitogen activated protein kinase and increase protein synthesis by enhancing gene expression. Beta1- and beta2-ARs as well as AC are considered to be regulated by PKA- and protein kinase C (PKC)-mediated phosphorylations directly; both PKA and PKC also regulate beta-AR indirectly through the involvement of beta-AR kinase (betaARK), beta-arrestins and Gbeta gamma-protein subunits. Genetic manipulation of different components and regulators of beta-AR signal transduction pathway by employing transgenic and knockout mouse models has provided insight into their functional and regulatory characteristics in cardiomyocytes. The genetic studies have also helped in understanding the pathophysiological role of PARK in heart dysfunction and therapeutic role of betaARK inhibitors in the treatment of heart failure. Varying degrees of defects in the beta-AR signal transduction system have been identified in different types of heart failure to explain the attenuated response of the failing heart to sympathetic stimulation or catecholamine infusion. A decrease in beta1-AR density, an increase in the level of G1-proteins and overexpression of betaARK are usually associated with heart failure; however, these attenuations have been shown to be dependent upon the type and stage of heart failure as well as region of the heart. Both local and circulating renin-angiotensin systems, sympathetic nervous system and endothelial cell function appears to regulate the status of beta-AR signal transduction pathway in the failing heart. Thus different components and regulators of the beta-AR signal transduction pathway appears to represent important targets for the development of therapeutic interventions for the treatment of heart failure.

Adenylyl Cyclases↗
PubMed2000

Role of oxidative stress in cardiovascular diseases.

OBJECTIVES: In view of the critical role of intracellular Ca2 overload in the genesis of myocyte dysfunction and the ability of reactive oxygen species (ROS) to induce the intracellular Ca2+-overload, this article is concerned with analysis of the existing literature with respect to the role of oxidative stress in different types of cardiovascular diseases. OBSERVATIONS: Oxidative stress in cardiac and vascular myocytes describes the injury caused to cells resulting from increased formation of ROS and/or decreased antioxidant reserve. The increase in the generation of ROS seems to be due to impaired mitochondrial reduction of molecular oxygen, secretion of ROS by white blood cells, endothelial dysfunction, auto-oxidation of catecholamines, as well as exposure to radiation or air pollution. On the other hand, depression in the antioxidant reserve, which serves as a defense mechanism in cardiac and vascular myocytes, appears to be due to the exhaustion and/or changes in gene expression. The deleterious effects of ROS are mainly due to abilities of ROS to produce changes in subcellular organelles, and induce intracellular Ca2+-overload. Although the cause-effect relationship of oxidative stress with any of the cardiovascular diseases still remains to be established, increased formation of ROS indicating the presence of oxidative stress has been observed in a wide variety of experimental and clinical conditions. Furthermore, antioxidant therapy has been shown to exert beneficial effects in hypertension, atherosclerosis, ischemic heart disease, cardiomyopathies and congestive heart failure. CONCLUSIONS: The existing evidence support the view that oxidative stress may play a crucial role in cardiac and vascular abnormalities in different types of cardiovascular diseases and that the antioxidant therapy may prove beneficial in combating these problems.

Calcium↗
PubMed2000

Mechanisms of ischemic preconditioning effects on Ca(2+) paradox-induced changes in heart.

The effects of ischemic preconditioning (IP) on changes in cardiac performance and sarcoplasmic reticulum (SR) function due to Ca(2+) paradox were investigated. Isolated perfused hearts were subjected to IP (three cycles of 3-min ischemia and 3-min reperfusion) followed by Ca(2+)-free perfusion and reperfusion (Ca(2+) paradox). Perfusion of hearts with Ca(2+)-free medium for 5 min followed by reperfusion with Ca(2+)-containing medium for 30 min resulted in a dramatic decrease in the left ventricular (LV) developed pressure and a marked increase in LV end-diastolic pressure. Alterations in cardiac contractile activity due to Ca(2+) paradox were associated with depressed SR Ca(2+)-uptake, Ca(2+)-pump ATPase, and Ca(2+)-release activities as well as decreased SR protein contents for Ca(2+)-pump and Ca(2+) channels. All these changes due to Ca(2+) paradox were significantly prevented in hearts subjected to IP. The protective effects of IP on Ca(2+) paradox changes in cardiac contractile activity as well as SR Ca(2+)-pump and Ca(2+)-release activities were lost when the hearts were treated with 8-(p-sulfophenyl)-theophylline, an adenosine receptor antagonist; KN-93, a specific Ca(2+)/calmodulin-dependent protein kinase II (CaMK II) inhibitor; or chelerythrine chloride, a protein kinase C (PKC) inhibitor. These results indicate that IP rendered cardioprotection by preventing a depression in SR function in Ca(2+) paradox hearts. Furthermore, these beneficial effects of IP may partly be mediated by adenosine receptors, PKC, and CaMK II.

Animals↗
PubMed2000

Ischemic preconditioning prevents I/R-induced alterations in SR calcium-calmodulin protein kinase II.

Although Ca(2+)/calmodulin-dependent protein kinase II (CaMK II) is known to modulate the function of cardiac sarcoplasmic reticulum (SR) under physiological conditions, the status of SR CaMK II in ischemic preconditioning (IP) of the heart is not known. IP was induced by subjecting the isolated perfused rat hearts to three cycles of brief ischemia-reperfusion (I/R; 5 min ischemia and 5 min reperfusion), whereas the control hearts were perfused for 30 min with oxygenated medium. Sustained I/R in control and IP groups was induced by 30 min of global ischemia followed by 30 min of reperfusion. The left ventricular developed pressure, rate of the left ventricular pressure, as well as SR Ca(2+)-uptake activity and SR Ca(2+)-pump ATPase activity were depressed in the control I/R hearts; these changes were prevented upon subjecting the hearts to IP. The beneficial effects of IP on the I/R-induced changes in contractile activity and SR Ca(2+) pump were lost upon treating the hearts with KN-93, a specific CaMK II inhibitor. IP also prevented the I/R-induced depression in Ca(2+)/calmodulin-dependent SR Ca(2+)-uptake activity and the I/R-induced decrease in the SR CaMK II activity; these effects of IP were blocked by KN-93. The results indicate that IP may prevent the I/R-induced alterations in SR Ca(2+) handling abilities by preserving the SR CaMK II activity, and it is suggested that CaMK II may play a role in mediating the beneficial effects of IP on heart function.

Animals↗
PubMed2000

Beneficial effects of vitamin E treatment in acute myocardial infarction.

BACKGROUND: Vitamin E (Vit E), an antioxidant, is considered to prolong survival in patients and animals after myocardial infarction. Because myocardial infarction is associated with arrhythmia and heart dysfunction, this study tested the hypothesis that early treatment with Vit E reduces mortality because of its protective effects against arrhythmia and cardiac dysfunction induced by acute myocardial infarction. METHODS: Rats were randomly divided into 4 groups: sham control, myocardial infarcted, Vit E-treated sham control, and Vit E-treated infarcted animals. Myocardial infarction was induced by ligation of the left anterior descending coronary artery. Treated animals received Vit E (25 mg/kg/d) through a gastric tube beginning 1 hour after the coronary occlusion, whereas control rats received tap water. RESULTS: Electrocardiograms (lead II) at 1, 3, 7, and 21 days after coronary occlusion in the untreated animals showed ST-segment elevation, abnormal Q waves, premature ventricular complex (PVC), and QTc prolongation. Conversely, Vit E-treated rats showed attenuated ST-segment changes, fewer abnormal Q waves, and decreased incidence of PVC after coronary occlusion. Total mortality was reduced from 38% to 16%, whereas the infarct size was decreased from 44.2% to 22.3% in infarcted rats treated with Vit E. The depression in left ventricular function as well as elevation of malondialdehyde content and conjugated diene formation in the 21-day infarcted rat hearts were prevented by Vit E treatment. CONCLUSION: These results indicate that Vit E may exert beneficial effects on the heart by reducing oxidative stress in acute myocardial infarction.

Animals↗
PubMed2000

Effect of beta-adrenoceptor blockers on sarcoplasmic reticular function and gene expression in the ischemic-reperfused heart.

Although beta-adrenoceptor (beta-AR) blockers are used for the treatment of ischemic heart disease, the mechanisms of their beneficial actions have not been fully elucidated. In view of the role of sarcoplasmic reticular (SR) abnormalities in cardiac dysfunction due to ischemia-reperfusion (I/R), we examined the effects of beta-AR blockers on the I/R-induced changes in SR Ca(2+) uptake and release, as well as the protein contents and gene expression of ryanodine receptor, SR Ca(2+)-pump, phospholamban, and calsequestrin. I/R in isolated rat hearts was induced by stopping the perfusion for 30 min and then reperfusing the ischemic hearts for 60 min. Hearts were treated with or without 10 microM atenolol, a beta(1)-specific blocker, or 10 microM propranolol, a nonspecific beta-blocker, 10 min before inducing ischemia as well as during the reperfusion period. I/R depressed cardiac performance, SR Ca(2+) uptake, and Ca(2+) release activities, protein contents, as well as Ca(2+)/calmodulin-dependent protein kinase and cAMP-dependent protein kinase-mediated phosphorylations, significantly. The mRNA levels for SR Ca(2+) pump, ryanodine receptors, phospholamban, and calsequestrin were also reduced by I/R. All these changes due to I/R were partially prevented by beta-AR blocker treatment. The results indicate that the beneficial effects of beta-AR blockers on cardiac performance in the I/R hearts may be related to the prevention of changes in SR Ca(2+) uptake and release activities, protein contents, as well as Ca(2+)/calmodulin-dependent protein kinase and cAMP-dependent protein kinase phosphorylations of SR proteins. On the other hand, the protection of I/R-induced alterations in mRNA levels for SR proteins by beta-AR blockers suggests cardiac SR gene expression as a molecular site of their cardioprotective action.

Adrenergic beta-Antagonists↗
PubMed2000

Role of cardiac renin-angiotensin system in sarcoplasmic reticulum function and gene expression in the ischemic-reperfused heart.

The aim of this study was to explore the possible participation of cardiac renin-angiotensin system (RAS) in the ischemia-reperfusion induced changes in heart function as well as Ca2+-handling activities and gene expression of cardiac sarcoplasmic reticulum (SR) proteins. The isolated rat hearts, treated for 10 min without and with 30 microM captopril or 100 microM losartan, were subjected to 30 min ischemia followed by reperfusion for 60 min and processed for the measurement of SR function and gene expression. Attenuated recovery of the left ventricular developed pressure (LVDP) upon reperfusion of the ischemic heart was accompanied by a marked reduction in SR Ca2+-pump ATPase, Ca2+-uptake and Ca2+-release activities. Northern blot analysis revealed that mRNA levels for SR Ca2+-handling proteins such as Ca2+-pump ATPase (SERCA2a), ryanodine receptor, calsequestrin and phospholamban were decreased in the ischemia-reperfused heart as compared with the non-ischemic control. Treatment with captopril improved the recovery of LVDP as well as SR Ca2+-pump ATPase and Ca2+-uptake activities in the postischemic hearts but had no effect on changes in Ca2+-release activity due to ischemic-reperfusion. Losartan neither affected the changes in contractile function nor modified alterations in SR Ca2+-handling activities. The ischemia-reperfusion induced decrease in mRNA levels for SR Ca2+-handling proteins were not affected by treatment with captopril or losartan. The results suggest that the improvement of cardiac function in the ischemic-reperfused heart by captopril is associated with the preservation of SR Ca2+-pump activities; however, it is unlikely that this action of captopril is mediated through the modification of cardiac RAS. Furthermore, cardiac RAS does not appear to contribute towards the ischemia-reperfusion induced changes in gene expression for SR Ca2+-handling proteins.

Animals↗
PubMed1999

Subcellular remodeling and heart dysfunction in cardiac hypertrophy due to pressure overload.

Rats were treated with etomoxir, an inhibitor of palmitoyltransferase-1, to examine the role of a shift in myocardial metabolism in cardiac hypertrophy. Pressure overload was induced by abdominal aorta banding for 8 weeks. Sham-operated animals served as control. Left ventricular dysfunction, as reflected by decreased LVDP, +dP/dt, -dP/dt, and elevated LVEDP in the pressure overloaded animals, was improved by treatment with etomoxir. Cardiac hypertrophy in pressure-overload rats decreased the sarcoplasmic reticular (SR) Ca2+ uptake and Ca2+ release as well as myofibrillar Ca(2+)-stimulated ATPase and myosin Ca(2+)-ATPase activities; these changes were attenuated by treatment with etomoxir. Steady-state mRNA levels for alpha- and beta-myosin heavy chains, SR Ca(2+)-pump, and protein content of SR Ca(2+)-pump were reduced in hypertrophied hearts; these alterations were prevented by etomoxir treatment. The results indicate that modification of changes in myocardial metabolism by etomoxir may prevent remodeling of myofibrils and SR membrane and thereby improve cardiac function in hypertrophied heart.

Animals↗
PubMed1999

Alterations in cardiac membrane beta-adrenoceptors and adenylyl cyclase due to hypochlorous acid.

Although neutrophils and eosinophils are known to produce hypochlorous acid (HOCI) at the site of cardiac injury, the exact role of this toxic oxidant on the signal transduction mechanism in the heart is not clear. In this study, the effects of HOCI on beta-adrenoceptors, G-proteins and adenylyl cyclase activity were assessed by incubating rat heart membranes with HOCl. The basal as well as forskolin-, NaF-, 5-guanylylimidodiphosphate-, and isoproterenol-stimulated adenylyl cyclase activities were depressed by incubating cardiac membranes with HOCl. While both the density and affinity of the beta1-adrenoceptors were decreased by treatment of cardiac membranes with HOCl, the characteristics of the beta2-adrenoceptors were not modified significantly. Although cholera toxin-stimulated adenylyl cyclase activity, cholera toxin-catalyzed ADP-ribosylation and stimulatory guanine nucleotide binding protein immunoreactivity were depressed by HOCl, the pertussis toxin-stimulated adenylyl cyclase activity, pertussis toxin-catalyzed ADP ribosylation and inhibitory guanine nucleotide binding protein immunoreactivity were unaltered by HOCl. The presence of L-methionine in the incubation medium prevented the HOCl-induced alterations in adenylyl cyclase activities and characteristics of beta1-adrenoceptors. These results suggest that HOCl may be one of the factors attenuating the beta-adrenoceptor linked signal transduction mechanism in conditions such as ischemic heart disease.

Adenosine Diphosphate↗
PubMed1999

Pyridoxal 5'-phosphate is an ATP-receptor antagonist in freshly isolated rat cardiomyocytes.

Although extracellular ATP is considered to exert a positive inotropic action on the myocardium through purinoceptors, very little information is available regarding interventions which may modify the actions of ATP on the heart. We report here that pyridoxal 5'-phosphate (PLP), an active form of vitamin B6, shows antagonism towards ATP-induced positive inotropic effect in isolated perfused rat hearts, ATP-induced increase in [Ca2+] in freshly isolated adult cardiomyocytes and ATP-binding in cardiac sarcolemma; ED50 for PLP in each of these cases varied from 10-15 microM. PLP (5-50 microM) was observed to antagonize the positive inotropic effect of ATP but did not modify the action of isoproterenol in the isolated perfused heart. Preincubation of cardiomyocytes with 1-50 microM PLP prevented the ATP-induced increase in [Ca2+]i in a concentration-dependent manner but showed no effect on the KCl-induced increase in [Ca2+]i. Creatine phosphate and Na2HPO4 as well as vitamin B6-related compounds, such as pyridoxine, pyridoxal, 4-deoxypyridoxine and isonicotinic acid hydrazide showed no effect on the ATP-induced increase in [Ca2+]i in cardiomyocytes. Furthermore, different concentrations of PLP (1-50 microM) were shown to inhibit the specific ATP gamma S binding at both the high and low affinity sites in the cardiac sarcolemmal membrane; adrenoceptor and Ca2+-channel inhibitors did not affect the ATP-binding. It is concluded that PLP may antagonize the actions of ATP on the heart in a selective manner and both pyridoxal and phosphate moieties are essential for its action. Furthermore, it is suggested that PLP may serve as a valuable tool for monitoring the role of purinoceptors in cellular function.

Adenosine Triphosphate↗
PubMed1999

Palmitoyl carnitine increases intracellular calcium in adult rat cardiomyocytes.

Earlier studies have demonstrated that palmitoyl carnitine (PC), a long chain acyl carnitine, accumulates in the ischemic myocardium. Although perfusion of hearts with PC is known to induce contractile dysfunction which resembles ischemic contracture, the mechanisms underlying this derangement are not clear. In this study, we examined the effect of exogenous PC on the intracellular concentration of calcium ([Ca(2+)](i)) in freshly isolated cardiomyocytes from adult rat hearts. The results showed that PC elevated [Ca(2+)](i)in a dose-dependent (5-20 microm) manner; 15 microm PC evoked a marked and reversible increase in [Ca(2+)](i)without having any significant action on cell viability. The PC (15 microm)-induced increase in [Ca(2+)](i)was slightly depressed but delayed in the absence of extracellular Ca(2+). Pre-incubation of cardiomyocytes with sarcolemmal (SL) l -type Ca(2+)-channel blockers, verapamil or diltiazem, and inhibitors of SL Na(+)-Ca(2+)exchanger such as Ni(2+)or amiloride, depressed the PC-evoked increase in [Ca(2+)](i)significantly. Ouabain, a Na(+)-K(+)ATPase inhibitor, and low concentrations of extracellular Na(+)enhanced the PC-induced increase in [Ca(2+)](i). Depletion of the sarcoplasmic reticulum (SR) Ca(2+)stores by low micromolar concentrations of ryanodine (a SR Ca(2+)-release channel activator) or by thapsigargin (a SR Ca(2+)-pump ATPase inhibitor) depressed the PC-mediated increase in [Ca(2+)](i). Combined blockade of the l -type Ca(2+)channel, Na(+)-Ca(2+)exchanger and the SR Ca(2+)-pump had an additive inhibitory effect on the PC response. These observations suggest that the PC-induced increase in [Ca(2+)](i)is dependent on both Ca(2+)-influx from the extracellular space and Ca(2+)-release from the SR stores. Thus, the accumulation of PC in the myocardium may be partly responsible for the occurrence of intracellular Ca(2+)overload in ischemic heart.

Animals↗
PubMed1999

Captopril treatment improves the sarcoplasmic reticular Ca(2+) transport in heart failure due to myocardial infarction.

Although captopril, an angiotensin-converting enzyme (ACE) inhibitor, has been shown to exert a beneficial effect on cardiac function in heart failure, its effect on the status of sarcoplasmic reticulum (SR) Ca(2+) transport in the failing heart has not been examined previously. In order to determine whether captopril has a protective action on cardiac function, as well as cardiac SR Ca(2+)-pump activity and gene expression, a rat model of heart failure due to myocardial infarction was employed in this study. Sham operated and infarcted rats were given captopril (2 g/l) in drinking water; this treatment was started at either 3 or 21 days and was carried out until 8 weeks after the surgery. The untreated animals with myocardial infarction showed increased heart weight and elevated left ventricular end diastolic pressure, reduced rates of pressure development and pressure fall, as well as depressed SR Ca(2+) uptake and Ca(2+)-stimulated ATPase activities in comparison with the sham control group. These hemodynamic and biochemical changes in the failing hearts were prevented by treatment of the infarcted animals with captopril. Likewise, the observed reductions in the SR Ca(2+) pump and phospholamban protein contents, as well as in the mRNA levels for SR Ca(2+) pump ATPase and phospholamban, in the failing heart were attenuated by captopril treatment. These results suggest that heart failure is associated with a defect in the SR Ca(2+) handling and a depression in the gene expression of SR proteins; the beneficial effect of captopril in heart failure may be due to its ability to prevent remodeling of the cardiac SR membrane.

Animals↗
PubMed1999

Beneficial effects of propionyl L-carnitine on sarcolemmal changes in congestive heart failure due to myocardial infarction.

OBJECTIVE: Earlier studies have revealed sarcolemmal (SL) defects in congestive heart failure due to myocardial infarction; however, the mechanisms of SL changes in the failing heart are poorly understood. Since congestive heart failure is associated with various metabolic abnormalities including a deficiency of carnitine, we examined the effects of propionyl L-carnitine, a carnitine derivative, in animals with congestive heart failure. METHODS: For this purpose, heart failure in rats was induced by occluding the coronary artery and 3 weeks later the animals were treated with 100 mg/kg (i.p. daily) propionyl L-carnitine for 4 weeks. The sham control group received saline injections. The animals were assessed for their left ventricular function. SL membranes were examined for Na(+)-K+ ATPase, Na(+)-Ca2+ exchange and adenylate cyclase activities. RESULTS: A marked improvement in the attenuated left ventricular function of the experimental animals was seen upon treatment with propionyl L-carnitine. The SL adenylyl cyclase activities in control, untreated failing hearts and treated failing hearts were 590 +/- 36, 190 +/- 22 and 320 +/- 21 pmol cAMP/mg/10 min, whereas the SL Na(+)-K+ ATPase activities were 35.7 +/- 2.8, 22.5 +/- 2.4 and 30.1 +/- 2.8 mumol Pi/mg/h, respectively. Furthermore, the SL Na(+)-dependent Ca(2+)-uptake activity, which decreased in the failing hearts (4.6 +/- 0.4 vs. 9.3 +/- 0.7 nmol Ca2+/mg/2 s for control), was improved (6.8 +/- 0.5 nmol Ca2+/mg/2 s) significantly following treatment with propionyl L-carnitine. CONCLUSION: These results indicate that metabolic therapy with propionyl L-carnitine may attenuate defects in the SL membrane and thus may improve heart function in congestive heart failure due to myocardial infarction.

Adenylyl Cyclases↗
PubMed1999

Differential changes in cardiac myofibrillar and sarcoplasmic reticular gene expression in alloxan-induced diabetes.

In order to examine the relationship between heart dysfunction and subcellular abnormalities as well as molecular mechanisms during the development of diabetes, we studied changes in cardiac performance, myofibrillar as well as sarcoplasmic reticular (SR) activities, and cardiac gene expression at different time intervals upon inducing diabetes in rats by an injection of alloxan (65 mg/kg; i.v.). Cardiac dysfunction was associated with a depression in myofibrillar Ca2+-stimulated ATPase and changes in myosin isozyme composition at 2-12 weeks of inducing diabetes. A reduction in SR Ca2+-uptake and Ca2+-pump (SERCA2) activities was evident at 10 days to 12 weeks of inducing diabetes. Alterations in cardiac function during 2-12 weeks of diabetes show a linear relationship with changes in myofibrils and SR membranes. Furthermore, alterations in cardiac function as well as myofibrillar and SR activities in 4 week diabetic animals were normalized upon treatment with insulin for 4 weeks. The steady-state mRNA abundance for alpha-myosin heavy chain in the heart was decreased at 2 and 3 weeks but was unchanged at 5 and 6 weeks, whereas mRNA levels for beta-myosin heavy chain remained elevated during 2-6 weeks after inducing diabetes. SERCA2 mRNA abundance in diabetic heart was significantly increased at 3 and 5 weeks but was unaltered at 2 and 6 weeks. These results support the view that heart dysfunction in diabetes may be a consequence of myofibrillar and SR abnormalities; however, defects in myofibrillar proteins, unlike those in the SR membranes, appear to be due to changes in their gene expression.

Animals↗
PubMed1999

Immunolocalization of the sarcolemmal Ca2+/Mg2+ ecto-ATPase (myoglein) in rat myocardium.

Cardiac plasma membrane Ca2+/Mg2+ ecto-ATPase (myoglein) requires millimolar concentrations of either Ca2+ or Mg2+ for maximal activity. In this paper, we report its localization by employing an antiserum raised against the purified rat cardiac Ca2+/Mg2+ ATPase. As assessed by Western blot analysis, the antiserum and the purified immunoglobulin were specific for Ca2+/Mg2+ ecto-ATPase; no cross reaction was observed towards other membrane bound enzymes such as cardiac sarcoplasmic reticulum Ca(2+)-pump ATPase or sarcolemmal Ca(2+)-pump ATPase. On the other hand, the cardiac Ca2+/Mg2+ ecto-ATPase was not recognized by antibodies specific for either cardiac sarcoplasmic reticulum Ca(2+)-pump ATPase or plasma membrane Ca(2+)-pump ATPase. Furthermore, the immune serum inhibited the Ca2+/Mg2+ ecto-ATPase activity of the purified enzyme preparation. Immunofluorescence of cardiac tissue sections and neonatal cultured cardiomyocytes with the Ca2+/Mg2+ ecto-ATPase antibodies indicated the localization of Ca2+/Mg2+ ecto-ATPase in association with the plasma membrane of myocytes, in areas of cell-matrix or cell-cell contact. Staining for the Ca2+/Mg2+ ecto-ATPase was not cardiac specific since the antibodies detected the presence of membrane proteins in sections from skeletal muscle, brain, liver and kidney. The results indicate that Ca2+/Mg2+ ecto-ATPase is localized to the plasma membranes of cardiomyocytes as well as other tissues such as brain, liver, kidney and skeletal muscle.

Adenosine Triphosphatases↗
PubMed1999

Status of Ca2+/calmodulin protein kinase phosphorylation of cardiac SR proteins in ischemia-reperfusion.

Although the sarcoplasmic reticulum (SR) is known to regulate the intracellular concentration of Ca2+ and the SR function has been shown to become abnormal during ischemia-reperfusion in the heart, the mechanisms for this defect are not fully understood. Because phosphorylation of SR proteins plays a crucial role in the regulation of SR function, we investigated the status of endogenous Ca2+/calmodulin-dependent protein kinase (CaMK) and exogenous cAMP-dependent protein kinase (PKA) phosphorylation of the SR proteins in control, ischemic (I), and ischemia-reperfused (I/R) hearts treated or not treated with superoxide dismutase (SOD) plus catalase (CAT). SR and cytosolic fractions were isolated from control, I, and I/R hearts treated or not treated with SOD plus CAT, and the SR protein phosphorylation by CaMK and PKA, the CaMK- and PKA-stimulated Ca2+ uptake, and the CaMK, PKA, and phosphatase activities were studied. The SR CaMK and CaMK-stimulated Ca2+ uptake activities, as well as CaMK phosphorylation of Ca2+ pump ATPase (SERCA2a) and phospholamban (PLB), were significantly decreased in both I and I/R hearts. The PKA phosphorylation of PLB and PKA-stimulated Ca2+ uptake were reduced significantly in the I/R hearts only. Cytosolic CaMK and PKA activities were unaltered, whereas SR phosphatase activity in the I and I/R hearts was depressed. SOD plus CAT treatment prevented the observed alterations in SR CaMK and phosphatase activities, CaMK and PKA phosphorylations, and CaMK- and PKA-stimulated Ca2+ uptake. These results indicate that depressed CaMK phosphorylation and CaMK-stimulated Ca2+ uptake in I/R hearts may be due to a depression in the SR CaMK activity. Furthermore, prevention of the I/R-induced alterations in SR protein phosphorylation by SOD plus CAT treatment is consistent with the role of oxidative stress during ischemia-reperfusion injury in the heart.

Animals↗