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J M Capasso

Publications and source records attributed to J M Capasso.

At least 109 records · Page 6Linked to original sources
PubMed1984

Translocation of adenosine 3'-phosphate 5'-phosphosulfate into rat liver Golgi vesicles.

The translocation of adenosine 3'-phosphate 5'-phosphosulfate (PAPS) across rat liver Golgi-derived vesicles has been studied. Vesicles of the same topographical orientation as in vivo were incubated with a mixture of [adenine-8-3H]PAPS and [35S]PAPS. The tritium to radiolabeled sulfur ratio of the incubation medium was 1.73 +/- 0.03 while that in the vesicles was 1.82 +/- 0.13. This strongly suggests that the entire PAPS molecule was being translocated across the Golgi vesicle membrane even though intact PAPS could not be detected within the vesicles. Translocation of PAPS resulted in accumulation of solutes within vesicles. This accumulation was temperature dependent, saturable (apparent Km = 0.7 microM; Vmax = 25 pmol/mg of protein/10 min), and inhibited by the substrate analogue 3',5'-ADP but not by 2',5'-ADP. Translocation of PAPS was inhibited following treatment of Golgi vesicles with Pronase under conditions in which the activity of a lumenal Golgi membrane marker such as sialyltransferase was not. This result is consistent with the existence of a PAPS carrier protein, portions of which face the cytoplasmic side of the Golgi membrane.

Adenine Nucleotides↗
PubMed1984

Mechanisms of glycosylation and sulfation in the Golgi apparatus: evidence for nucleotide sugar/nucleoside monophosphate and nucleotide sulfate/nucleoside monophosphate antiports in the Golgi apparatus membrane.

The mechanism of translocation in vitro of sugar nucleotides and adenosine 3'-phosphate 5'-phosphosulfate (PAPS) into the lumen of rat liver Golgi apparatus vesicles has been studied. It has been previously shown that the Golgi apparatus membrane has specific carrier proteins for PAPS and sugar nucleotides. We now report that translocation of the above nucleotide derivatives across Golgi membranes occurs via a coupled equimolar exchange with the corresponding nucleoside monophosphates. An initial incubation of Golgi vesicles with GDP-fucose radiolabeled in the guanidine ring resulted in accumulation within the lumen of radiolabeled GMP. Exit of GMP from these vesicles was specifically dependent on the entry of (additional) GDP-fucose into the vesicles (GDP-mannose and other sugar nucleotides had no effect). GDP-fucose-stimulated exit of GMP was temperature dependent, was blocked by inhibitors of GDP-fucose transport, such as 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid, and appeared to be equimolar with GDP-fucose entry. Preliminary evidence for specific, equimolar exchange of CMP-N-acetylneuraminic acid with CMP, PAPS with 3'-AMP, and UDP-galactose and UDP-N-acetylglucosamine with UMP was also obtained. These results strongly suggest the existence of different antiport proteins within the Golgi membrane that mediate the 1:1 exchange of sugar nucleotides or PAPS with the corresponding nucleoside monophosphate. Such proteins may have a regulatory role in glycosylation and sulfation reactions within the Golgi apparatus.

Adenine Nucleotides↗
PubMed1984

Combined renovascular hypertension and diabetes in rats: a new preparation of congestive cardiomyopathy.

Myocardial function, electrophysiologic characteristics, and structure were studied in rats with both renovascular hypertension and streptozotocin-induced diabetes (HD). Ventricular papillary muscles from untreated rats with HD showed a marked slowing of isometric and isotonic contractions. Peak developed tension and peak shortening were preserved, except in one animal with findings of congestive heart failure. Transmembrane action potentials increased fivefold in duration. Myocardial interstitial fibrosis was frequently observed. Physiologic parameters of rats with HD treated by left nephrectomy, captopril, and insulin were very similar to those of age-matched controls. The mortality rate of rats with HD was 43% over 5 to 6 months in the first study. In a second study, spontaneously dying rats with HD were compared with those deliberately killed. A 55% mortality was observed over 7 months. Myocardial structural damage and histologic evidence of congestive heart failure were more frequent in spontaneously dying rats with HD. Combined renovascular hypertension and diabetes in rats appears to be a new preparation of congestive cardiomyopathy.

Action Potentials↗
PubMed1984

Cardiac conditioning ameliorates cardiac dysfunction associated with renal hypertension in rats.

To explore the effect of physiologic hypertrophy superimposed on pathologic hypertrophy, hearts from female control rats (C), renal hypertensive rats (H), rats conditioned with a 10-12 wk swimming program (Sw), and hypertensive rats trained by the swimming program (H-Sw) were perfused in an isolated working rat-heart apparatus. Systolic blood pressure was approximately 100 mmHg in C and Sw and was 160 mmHg in H and H-Sw. The swimming program had no effect on blood pressure. Compared with C, heart weight was increased by 30% in Sw, 47% in H, and 77% in H-Sw. At high preload and afterload, cardiac output (milliliters per gram dry LV weight) was decreased in H, increased in Sw, and partially restored towards normal in H-Sw. Ejection fraction, percent fractional shortening, and mean velocity of circumferential fiber shortening were enhanced in Sw, depressed in H, and normalized in H-Sw when compared with C. Coronary flow and myocardial oxygen consumption in this series of hearts were depressed in H, with no restoration in H-Sw, but coronary effluent lactate/pyruvate ratios were only elevated in the hearts of H-Sw. Coronary vascular responses were examined in a second series of experiments which used microspheres. In this series, the depressed coronary flow observed in H was partially restored towards normal in H-Sw and the inner/outer myocardial flow ratio was normal when hearts were perfused at 140 cm aortic pressure but was somewhat depressed in both H and H-Sw when the hearts were perfused at 80 cm aortic pressure. These studies demonstrate that hypertrophic hearts from renal hypertensive rats have diminished coronary flow and depressed cardiac function when they are studied in the isolated working heart apparatus, yet there is no evidence of myocardial ischemia. Superimposition of a chronic swimming program results in increased hypertrophy but restoration of cardiac function partially or completely to normal. Thus, pathologic and physiologic hypertrophy are biologically distinct entities. Physiologic hypertrophy may partially ameliorate the defects associated with pathologic hypertrophy.

Animals↗
PubMed1984

Coronary microvascular abnormalities in the hypertensive-diabetic rat. A primary cause of cardiomyopathy?

The authors have continued their investigation of the hypertensive-diabetic (HD) rat by evaluating changes in the myocardial microvasculature in this model. Perfusion of HD animals in vivo with a silicone rubber solution revealed numerous areas of microvascular tortuosity, focal constrictions, and microaneurysm formation. These alterations were present to a lesser extent in normoglycemic hypertensive (H) rats, and were distinctly rare in normotensive diabetic rats and unaffected control animals. Quantitation of these vascular lesions revealed highly significant differences between HD animals and the other three groups, with hypertensive rats intermediate between HD rats and diabetic control rats. Areas of pronounced arteriolar constriction were also identified in the HD and H animals with the use of serial sections of Epon-embedded myocardium. It is believed that these lesions represent dynamic changes in the microcirculation, which may cause segmental reperfusion injury to the myocardium, leading to focal replacement fibrosis. Interstitial scarring may result from increased leakiness of small vessels exacerbated by the combined disease. The authors propose that the additive effects of hypertension and diabetes mellitus on the myocardial microcirculation may be a primary cause of cardiomyopathy in this model of human disease.

Animals↗
PubMed1983

Effects of age on mechanical and electrical performance of rat myocardium.

Left ventricular papillary muscles were isolated from male Fischer rats at 3, 6, 12, and 24 mo of age. Mechanical performance and transmembrane action potential characteristics were recorded simultaneously. Contractile protein enzyme activity was determined in the same hearts from which papillary muscles were used for acquisition of mechanical and electrical information. There was an age-related increase in the isometric time to peak tension and time to half relaxation with no age-related change in peak isometric developed tension. Resting tension showed a significant increase at both 12 and 24 mo of age. Although no significant change was noted in peak rate of tension rise (+T') or fall (-T'), there was a significant age-related prolongation in the time to +T' and -T'. Isotonically, peak shortening decreased in 24-mo-old animals. Time to peak shortening increased, whereas peak velocity of muscle shortening decreased from 3 to 24 mo of age. A significant and progressive prolongation was noted in the duration of the transmembrane action potential at 50% and 75% repolarization. In addition an age-related progressive decline was seen in contractile protein enzyme activity. These biochemical and electrophysiological alterations may help to explain the contractile modifications during aging.

Action Potentials↗
PubMed1982

Post-natal developmental changes in myocardial contractility of the female Wistar rat.

The intrinsic contractile properties of papillary muscles isolated from female Wistar rats during post-natal development were examined. In addition, the myocardial responsiveness to certain inotropic interventions was studied. In muscles from 60-day-old animals, the velocity of shortening was markedly greater than muscles from animals greater than or equal to 180 days old. These findings occurred in the presence and absence of added norepinephrine or calcium and over a wide range of contraction frequency. No major age-related differences in responsiveness to the various inotropic agents was observed. Isometric tension was significantly higher in muscles from animals greater than or equal to 180 days of age when compared to 60-day-old rats. Thus, post-natal development profoundly affects the intrinsic contractile state of cardiac muscle, with the force of contraction increasing and the speed of shortening decreasing as animals age.

Aging↗
PubMed1982

Effects of experimental phosphate deficiency on action potential characteristics and contractile performance of rat myocardium.

Chronic hypophosphataemia is associated with reversible depression in myocardial performance of the intact heart. To define the basis for this, were studied the mechanical and electrical properties of isolated left ventricular papillary muscles from rats with 6 weeks of phosphorus depletion (P6), 6 weeks of phosphorus repletion and age-matched controls (C). Muscles were perfused with Tyrode's solution (Ca2+ 2.4 mmol.liter-1, 7 = 4.0 mmol . litre-1, dextrose = 5.5 mmol . litre-1) and driven at 0.1 Hz. P6 muscles had slowed isometric relaxation (T1/2R), depressed velocity of shortening and relaxation and prolongation of the transmembrane action potential to 75% of complete repolarisation. These results suggest that the slow relaxation phase may be the result of the prolonged APD75 and that the depressed myocardial performance in the intact heart may be based on impaired relaxation and reduced the velocity of shortening associated with hypophosphataemia. This view is supported by our finding that these alterations are reversible with phosphate repletion.

Action Potentials↗
PubMed1982

Alterations in mechanical properties of rat papillary muscle during maturation.

Myocardial performance was measured during maturation using isolated left ventricular papillary muscles from female Wistar rats. Muscles were studied isometrically and isotonically, stimulated at 0.1 Hz, perfused with Tyrode solution having an external calcium concentration of 2.4 mM, and maintained at 30 degrees C. Heart and body weight increased rapidly during the first 6 mo and then stabilized. Peak isometric developed tension, time to peak isometric developed tension, and time to half relaxation increased substantially during the 1- to 10-mo period with little change in the peak rate of isometric tension rise and peak rate of isometric tension fall. No difference in resting tension was noted among any groups. Force-velocity curves from muscles from 2-, 6-, and 10-mo-old animals show a significant age-related decrease in the isotonic velocity of shortening by as much as 21% between 2 and 10 mo of age. Thus maturation profoundly affects the contractile state of cardiac muscle, with force of contraction increasing and velocity of shortening decreasing as a function of age in the rat.

Aging↗
PubMed1982

Contractile behavior of rat myocardium after reversal of hypertensive hypertrophy.

The effects of renovascular hypertension and its reversal on the contractile performance of papillary muscles from rats has been examined. Hypertension of 10 wk duration caused a 48% increase in heart weight and significant prolongations of isometric time to peak tension (TPT), time to half relaxation, and time to peak shortening (TPS). A significant depression in the velocity of shortening was observed in the 10-wk group. However, muscles from hypertensive rats were still able to maintain normal levels of peak isometric developed tension and peak shortening; this may be due to the observed prolongation of TPT and TPS, respectively. In addition, calcium-activated actomyosin ATPase activity was depressed in hearts of hypertensive animals. Reversal of hypertension was studied at 20 wk after the onset of hypertension (10 wk of hypertension followed by 10 wk of normotension). Contractile and biochemical alterations observed in hypertensive animals were reversed in rats undergoing this regime. Thus reversal of a gradually applied pressure overload resulted in the regression of mechanical and biochemical abnormalities associated with the pressure overload myocardial hypertrophy.

Adenosine Triphosphatases↗
PubMed1982

Reversible alterations in excitation-contraction coupling during myocardial hypertrophy in rat papillary muscle.

To investigate the possible role of an alteration in excitation-contraction coupling in cardiac hypertrophy, we compared simultaneously recorded action potentials along with isometric or isotonic contractions of normal and hypertrophied papillary muscles. Hypertrophy was produced by renal hypertension in rats. Hypertrophied papillary muscles were taken from rats that had been hypertensive for 10 [HBP (10)] or 20 [HBP (20)] weeks. Regression of changes induced by hypertrophy was studied in rats that had been hypertensive for 10 weeks and then made normotensive for 10 weeks by removal of the ischemic kidney. Papillary muscles from age-matched, sham-operated rats [SHAM (10), SHAM (20)] were used as controls. We found that HBP (10) rats had significantly longer action potentials than SHAM (10) rats and that difference in the action potential duration recorded during isotonic and isometric contractions was significantly different from SHAM (10) and HBP (10) rats. Peak developed tension was the same in HBP (10) and SHAM (10) muscles, but the duration of isometric contraction and time-to-peak shortening were longer in HBP (10) muscles. Similarly, whereas the peak tension was the same in HBP (20) and SHAM (20) muscles, the duration of the action potential and isometric contraction, as well as the time-to-peak tension, was longer in HBP (20) muscles. The longer values for action potential duration, isometric contraction, and time-to-peak tension in HBP (20) muscles returned to SHAM values in HBP (R) muscles. The functional relationship between contraction and the action potential time course was assessed by plotting action potential duration against four parameters of contraction: peak developed tension, time-to-peak tension, time-to-half relaxation, and time-to-peak shortening. Statistical analysis of these data showed a significant correlation between action potential duration and all four parameters of contraction in SHAM (10) and SHAM (20) muscles. In contrast, HBP (10) muscles showed a significant correlation between action potential duration and only two contractile parameters, whereas action potential duration did not correlate significantly with any of the contractile parameters in HBP (20) muscles. Remarkably, in HBP (R) preparations a significant correlation was restored between action potential duration and three of the four contractile parameters. The results of this study suggest that reversible cardiac hypertrophy is associated with reversible alterations in excitation-contraction coupling. The reversibility of the mechanical and electrical alterations that accompany hypertrophy suggests, in turn, that cardiac hypertrophy is an adaptive process.

Action Potentials↗
PubMed1981

Myocardial mechanical alterations during gradual onset long-term hypertension in rats.

Although a suddenly produced load leads to depressed myocardial contractility, the effects of a slowly induced physiological overload have not been defined. Therefore, a more gradual pressure overload was produced in female Wistar rats by hypertension due to constriction of the left renal artery. Hypertension (systolic blood pressure greater than or equal to 150 mmHg) developed within 3 wk, and blood pressure continued to increase for the next 5 wk. Heart weights in hypertensive animals were elevated by 34% after the onset of hypertension. Isometric and isotonic contractions from left ventricular papillary muscles were recorded at 5, 10, 20, and 30 wk after the onset of hypertension. Total and actively developed isometric tension at all initial muscle lengths were significantly greater in hypertensive animals throughout the 30-wk period. Time to peak tension and time to half relaxation were significantly prolonged. Force-velocity curves demonstrated a significant depression in velocity of shortening at all relative loads in hypertensive muscles that progressed with the duration of hypertension. These studies suggest that myocardial hypertrophy may impart the ability to maintain ventricular performance in terms of force development while speed of shortening decays.

Animals↗
PubMed1981

Glycogenolysis during anoxia in aged mouse heart.

Myocardial glycogen mobilization in response to anoxia has been studied in open-chested C57Bl/6NCrl male mice 6 and 24 months of age. During the 1st minute without oxygen, old animals utilized glycogen more rapidly than did young animals. However, during the 2nd minute of anoxia, young animals continued to utilize cardiac glycogen, whereas old animals did not. A direct correlation was noted between glycogen utilization and activation of myocardial phosphorylase activity (A+B forms). Moreover total myocardial phosphorylase declined during anoxia in old animals while showing no significant change in their younger counterparts. This age-related defect in glycogen mobilization suggests altered tolerance to anoxia in aged animals. The inability to mobilize myocardial glycogen may stem from the existence of an altered form of phosphorylase or from an altered environment in the aged heart.

Aging↗
PubMed1980

Altered myocardial mechanics in diabetic rats.

Diabetes mellitus is associated frequently with congestive heart failure in humans, even in the absence of associated coronary disease or hypertension. Nevertheless, the effects of the diabetic state on myocardial mechanics have not been studied. Accordingly, diabetes was induced in female Wistar rats by injection of streptozotocin (60 mg/kg). Left ventricular papillary muscles were studied 5, 10, and 30 weeks later and compared with controls. Relaxation was delayed significantly and velocity of shortening was depressed at all loads. However, the passive and active force-length curves, as well as the series elastic properties, were not altered. The changes in cardiac performance were found over a range of muscle lengths, stimulus frequencies, and bath concentrations of calcium, glucose, and norepinephrine. The duration of diabetes had no major effect on the mechanical changes observed. The possible influences of drug-induced cardiac toxicity, malnutrition, and altered thyroid hormone levels have been considered; the latter two factors could not be excluded completely from having some influence on the mechanical properties of diabetic cardiac muscle. Evidence is cited showing abnormalities in calcium uptake by sarcoplasmic reticulum and depressed actomyosin ATPase activity. Thus a cardiomyopathic state has been produced in the rat consequent to the induction of experimental diabetes mellitus. Various mechanisms for this entity have been suggested.

Animals↗
PubMed1978

Nucleic acids quantitation in polyacrylamide disc gels with a modified double beam spectrophotometer.

Quantitation of RNA and protein bands separated in polyacrylamide disc gel electrophoresis is time consuming and not reliable when performed after staining processes. The best theoretical approach is the use of absorption spectra of the samples. The present paper reports the construction of an efficient and inexpensive adapter to perform direct scanning of 100 mm gels in a Unicam SP-800 double beam spectrophotometer. Conditions for gel casting and electrophoresis were established for RNA. A linear response between 0.25 micrograms and 15 micrograms per individual peak was found with a quantitative limit of detection of 0.25 micrograms. Spectral analysis of each band can be performed allowing identification of samples as nucleotides and detection of contaminants.

Electrophoresis, Polyacrylamide Gel↗