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V Panagia

Publications and source records attributed to V Panagia.

121 records · Page 7Linked to original sources
PubMedDate not supplied

Interactions between cyclic AMP-dependent protein phosphorylation and lipid transmethylation reactions in isolated porcine cardiac sarcolemma.

Premethylation of purified porcine cardiac sarcolemma (SL) in the presence of 0.15, 10 and 150 microM S-adenosyl-L-methionine (AdoMet) did not change the phosphorylation of SL proteins catalyzed either by intrinsic cyclic AMP-dependent protein kinase (cAK) or by added catalytic (C) subunit of this enzyme. On the other hand, membrane exhibited increased lipid methyltransferase activity after preincubation with MgATP and C subunit. Prephosphorylation of membranes stimulated the total [3H]-methyl incorporation into SL lipids assayed at 0.15 microM [3H]AdoMet due to an enhancement of Vmax and without changes in the Km value for AdoMet. Analysis of the methylated lipid products revealed an increased methyl group incorporation into a nonpolar lipid fraction whereas phosphatidylethanolamine-N-methylation was not affected by phosphorylation. The results suggest that the cyclic AMP-mediated signal transduction at the level of cardiac SL is not affected by methylation-induced modifications of the membrane lipid microdomains. On the other hand, an intrinsic SL lipid methyltransferase activity is apparently not related to the N-methylation of phospholipids, is modulated by cyclic AMP-dependent protein phosphorylation.

Adenosine Triphosphate↗
PubMedDate not supplied

Kinetics of myocardial phospholipase D.

Myocardial phospholipase D (PLD) is located in different subcellular membranes, including sarcolemma (SL) and sarcoplasmic reticulum (SR). In this study, the kinetics of PLD-dependent hydrolytic and transphosphatidylation activities were examined in SL and SR fractions isolated from rat heart by measuring the formation of phosphatidic acid and phosphatidylethanol, respectively. The results showed that, compared to SR PLD, SL PLD had a higher Vmax, i.e. 373 vs. 70 nmol/mg protein/h for the hydrolytic activity and 415 vs. 60 nmol/mg protein/h for the transphosphatidylation activity. In comparison with the SR enzyme, SL PLD had a lower Km value for the hydrolytic activity (0.46 vs. 0.65 mM), buy a higher Km for the transphosphatidylation activity (225 vs. 179 mM). These distinctive kinetic parameters suggest that SL PLD and SR PLD may be isoforms of the enzyme and/or have different membrane domain. Therefore, SL- and SR-localized PLD activities may be under independent control mechanism(s) and play distinct roles in normal conditions and pathological processes.

Animals↗
PubMedDate not supplied

Sarcolemmal Na+-Ca2+ exchange and Ca2+-pump activities in cardiomyopathies due to intracellular Ca2+-overload.

In order to identify defects in Na+-Ca2+ exchange and Ca2+-pump systems in cardiomyopathic hearts, the activities of sarcolemmal Na+-dependent Ca2+ uptake, Na+-induced Ca2+ release, ATP-dependent Ca2+ uptake and Ca2+-stimulated ATPase were examined by employing cardiomyopathic hamsters (UM-X7.1) and catecholamine-induced cardiomyopathy produced by injecting isoproterenol into rats. The rates of Na+-dependent Ca2+ uptake, ATP-dependent Ca2+ uptake and Ca2+-stimulated ATPase activities of sarcolemmal vesicles from genetically-linked cardiomyopathic as well as catecholamine-induced cardiomyopathic hearts were decreased without any changes in Na+-induced Ca2+-release. Similar results were obtained in Ca2+-paradox when isolated rat hearts were perfused for 5 min with a medium containing 1.25 mM Ca2+ following a 5 min perfusion with Ca2+-free medium. Although a 2 min reperfusion of the Ca2+-free perfused hearts depressed sarcolemmal Ca2+-pump activities without any changes in Na+-induced Ca2+-release, Na+-dependent Ca2+ uptake was increased. These results indicate that alterations in the sarcolemmal Ca2+-efflux mechanisms may play an important role in cardiomyopathies associated with the development of intracellular Ca2+ overload.

Adenosine Triphosphatases↗
PubMedDate not supplied

Membrane phospholipids and adrenergic receptor function.

We have reviewed the effects on adrenergic receptors by membrane phospholipid alterations secondary to oxidative stress and phospholipases' activity. Experimental evidences indicate that the function of both alpha- and beta-adrenoceptors is regulated by their phospholipid microdomain; however, the underlying mechanism is still undefined. No information seems to be available on the influence of phospholipids on alpha 2-adrenoceptors and on all adrenoceptors' subtypes. Thus, further studies are necessary to clarify the role of membrane phospholipids in regulating the function of each member of the adrenergic receptor superfamily.

Animals↗
PubMedDate not supplied

A biphasic change in contractile proteins during the development of cardiac hypertrophy in pigs.

A non-failing hypertrophy of the left ventricle was produced in the pig heart by supravalvular banding of aorta for 4, 8 and 12 weeks and the myosin and myofibrillar adenosine triphosphatase activities were measured. A significant increase in myosin Ca2+-ATPase activity was seen at 4 weeks of hypertrophy, but at 8 and 12 weeks this activity was significantly decreased compared to sham control. Similar changes were also seen in actin-activated myosin ATPase activities at 4, 8 and 12 weeks of hypertrophy. There were no changes in the K+- and NH4+-EDTA-stimulated ATPAse activities of myosin. Basal ATPase activities of myofibrils were decreased at 4 and 8 weeks of hypertrophy and there was no change in this activity at 12 weeks of hypertrophy. Ca2+ stimulated ATPase activity of myofibrils was significantly increased at 4 weeks, normal at 8 weeks and significantly reduced at 12 weeks of hypertrophy. The changes in ATPase activities were not due to any alterations of proteins by high concentrations of salts during the purification of myosin. The non-hypertrophied right ventricle from the banded animals did not show any change in the basal or Ca2+ stimulated myofibrillar ATPase activities. It is suggested that hypertrophy of the myocardium is accompanied by specific changes in the enzyme activities of the contractile proteins and the biphasic responses may correlate with the functional state of the myocardium subjected to a chronic increase in pressure.

Adenosine Triphosphatases↗
PubMedDate not supplied

Structure-activity relationship of the effect of cis-unsaturated fatty acids on heart sarcolemmal phospholipase D activity.

This study examined the role of fatty acids on the phosphatidylcholine-specific phospholipase D (PLD) function of purified sarcolemmal (SL) membranes isolated from rat hearts. The enzyme's hydrolytic activity was determined by measuring [14C] phosphatidic acid formation from exogenous [14C] phosphatidylcholine (PtdCho) in the absence or presence of the sodium salts of various saturated or unsaturated long-chain fatty acids (FA). In certain experiments the enzyme was also assayed in the transphosphatidylation mode. Cis-unsaturation and free carboxyl groups were structural prerequisites for the stimulatory effect exerted by FA on SL PLD. The most effective compounds were arachidonate and oleate, which maximally activated PLD at 4 and 5 mM concentration, respectively. To verify if a detergent-like mechanism was involved in PLD activation, anionic, zwitterionic and non-ionic detergents were used. Only anionic taurodeoxycholate had a slight effect, which was about 7% of that achieved by arachidonate or oleate. These results suggest that cis-unsaturated FA activate cardiac sarcolemmal PLD by a mechanism(s) which seems to be unrelated to non-specific perturbation of the membrane.

Animals↗
PubMedDate not supplied

Altered lipid metabolism in the failing heart of cardiomyopathic hamsters (UM-X7.1).

The lipid composition of different anatomic regions of 150 day-old UM-X7.1 cardiomyopathic hamster and age-matched controls (Syrian golden hamsters) was examined. Cardiomyopathic hamsters exhibit a phospholipid to protein ratio higher than healthy animals in atria, whereas the contrary is true in the other anatomic regions examined. In all tissues the cholesterol to phospholipid ratio is higher in cardiomyopathic hamster than in controls. Healthy and UM-X7.1 hamsters differ substantially as far as the percent distribution of fatty acids in total lipids is concerned, the lipids from cardiomyopathic animals accumulating fatty acids of the omega-6 series and being relatively poor in monoenoic fatty acids. The different fatty acid composition of heart lipids appears to be a consequence of a generalized disturbance of the lipid metabolism in cardiomyopathic hamsters during congestive heart failure.

Animals↗
PubMedDate not supplied

Impairment of mitochondrial and sarcoplasmic reticular functions during the development of heart failure in cardiomyopathic (UM-X7.1) hamsters.

The oxidative phosphorylation as well as calcium transporting properties of heart mitochondria and calcium transport activities of the fragments of the sarcoplasmic reticulum (microsomes) were studied during the life span of cardiomyopathic hamsters (UM-X7.1). Control healthy hamsters of the same age group were used for comparison. No changes in the oxidative phosphorylation ability of cardiomyopathic mitochondria were seen at early and moderate stages of heart failure; however, at severe stages, mitochondrial respiratory functions, but not the ADP:0 ratio, were impaired. Both creatine phosphate and ATP contents were decreased without any significant changes in the ATPase activities of myofibrils from the failing hearts. Heart mitochondria from cardiomyopathic animals at severe stages of failure exhibited less calcium binding and uptake activities in comparison with the control values whereas no changes in the mitochondrial calcium binding and uptake were seen in cardiomyopathic hamsters which showed no clinical signs of heart failure. Although mitochondrial calcium binding in cardiomyopathic hearts at early and moderate stages of failure was decreased, mitochondrial calcium uptake was not significantly different from the control. Microsomal calcium binding activity, unlike calcium uptake activity, was decreased in the hearts of cardiomyopathic hamsters without any signs of heart failure. Both calcium binding and calcium uptake activities of microsomes from animals with early, moderate and severe heart failure were less in comparison with the control values but were not associated with any changes in the Ca2+-stimulated ATPase activity. These results suggest that changes in the process of mitochondrial energy production and mitochondrial Ca2+-transport may be secondary to other factors whereas alterations in the sarcoplasmic reticular Ca2+-transport may lead to the development of heart failure in the cardiomyopathic hamsters.

Adenosine Triphosphatases↗