Biomedical subjects

R T Fogaça

Publications and source records attributed to R T Fogaça.

6 recordsLinked to original sources

PubMed1998

Alterations of myocardial contraction associated with a structural heart defect in embryonic chicks.

Ablation of cardiac neural crest at stages 8-10 produces a structural heart defect (persistent truncus arteriosus, PTA) in embryonic chicks. PTA is associated with decreased myocardial contractility, as indicated by decreased left ventricular ejection fraction. We compared the force of small ventricular strips from normal and defective chick hearts. In intact muscle, ablation of the neural crest leads to a 30-50% decrease in twitch force at any level of extracellular Ca2+ (0.45-20 mM) at embryonic days (ED) 7 and 15, relative to sham-operated controls. These differences could reflect defects at the level of the contractile apparatus and/or in the excitation-contraction coupling process. To distinguish changes of the contractile apparatus, we used detergent skinned preparations. The maximal Ca(2+)-activated force (Fmax) at ED15 was not significantly different between control and experimental embryos. At ED 7, however, Fmax was reduced by 36% in experimental preparations. Electron-micrographs showed that the organization and orientation of the myofibrils was similar in experimental and control ventricles. At ED 14, however, the average myofibrillar diameter was significantly increased in experimental ventricles. The content of the major myofibrillar proteins (myosin heavy chain, actin, and tropomyosin), determined from polyacrylamide gel electrophoresis and Coomassie Blue staining, normalized to total protein, was not statistically different in experimental and control ventricles at ED7. At ED15, however, content of these proteins was doubled in experimental ventricles. These data suggest a possible defect of the contractile apparatus at both ED 7 and 15, since the ratio of Fmax/myosin is reduced in the experimental hearts.

Animals↗

PubMed1997

Effect of cardiac neural crest ablation on contractile force and calcium uptake and release in chick heart.

Cardiac neural crest ablation (CNCA) in the chick embryo at stages 8-10 results in reduced contractility of the heart that can be observed as early as stage 14. We found that intact trabeculae from embryonic day (E) 15 experimental animals after CNCA display an approximately 50% decrease in twitch force relative to sham-operated E15 control animals. In control and CNCA trabeculae skinned in Triton X-100 and bathed in our standard solutions, neither maximum Ca(2+)-activated force nor Ca2+ sensitivity of the contractile apparatus was significantly different. CNCA resulted in a marked reduction in the magnitude of the Ca2+ transient in trabeculae, estimated using fura 2 acetoxymethyl ester. CNCA had no effect on the half-time of Ca2+ loading by the sarcoplasmic reticulum (SR) of saponin skinned trabeculae at fixed Ca2+. However, it slightly reduced the Ca2+ sensitivity of Ca2+ uptake by the SR. Its most dramatic effect was to essentially abolish Ca(2+)-induced Ca2+ release from the SR. These effects on Ca2+ metabolism explain, in part, the decrease in the intracellular Ca2+ transient and myocardial contractility observed with CNCA.

Animals↗

PubMed1995

The effect of 2,3-butanedione 2-monoxime (BDM) on ventricular trabeculae from the avian heart.

2,3-butanedione 2-monoxime (BDM, 3-30 mM) decreased twitch force of intact ventricular trabeculae isolated from 19-day embryonic chick hearts in a dose-dependent manner. The responses to BDM were rapid and reversible. In an attempt to determine the cellular basis for the inhibitory effect of BDM, experiments were carried out on skinned muscle fibres and isolated myocytes. In trabeculae skinned with Triton X-100, BDM depressed maximum calcium activated force (Fmax) with an IC50 of 14 mM. At 3 mM BDM, the proportional decrease in twitch force in intact tissue was similar to that of Fmax in skinned tissue. At higher BDM concentrations (10 and 30 mM), however, the proportional decrease in twitch force was greater than that of Fmax. BDM (up to 10 mM) had no effect on the normalized force-pCa relationship. In saponin-skinned preparations, BDM (3 and 30 mM) released calcium from the fully loaded sarcoplasmic reticulum to a slightly greater extent in the absence of calcium (pCa 8.5) than in the presence of a fixed level of free calcium (pCa 5.5). Whole cell patch clamping of freshly isolated chick myocytes demonstrated that BDM caused a dose-dependent decrease in the T- and L-type calcium current. Therefore, at low BDM concentrations (3 mM), the decrease in twitch force can be ascribed predominantly to depression of the contractile apparatus while, at higher concentrations of BDM, there is an additional inhibitory effect of BDM on excitation-contraction coupling.

Animals↗

PubMed1993

Influence of ionic strength on contractile force and energy consumption of skinned fibers from mammalian and crustacean striated muscle.

Increased ionic strength decreases maximal calcium-activated force (Fmax) of skinned muscle fibers via mechanisms that are incompletely understood. In detergent-skinned fibers from either rabbit (psoas) or lobster (leg or abdomen), Fmax in KCl-containing solutions was less than in potassium methanesulfonate (KMeSO3), which we showed previously was the least deleterious salt for adjusting ionic strength. In either salt, lobster fibers were considerably less sensitive to elevated ionic strength than rabbit fibers. Trimethylamine N-oxide (TMAO, a zwitterionic osmolyte found in high concentration in cells of salt-tolerant animals) increased Fmax, especially in high KCl solutions. In this regard, TMAO was more effective than a variety of other natural or synthetic zwitterions. In rabbit fibers, increasing ionic strength decreases Fmax but has little effect on contractile ATPase rate measured simultaneously using a linked-enzyme assay. Thus high salt increases the tension-cost of contraction (i.e. ratio ATPase/Fmax). At both high and low salt, TMAO decreases tension-cost. Given a simple two-state model of the cross-bridge cycle, these data indicate that ionic strength and TMAO affect the apparent detachment rate constant. High ionic strength KCl solutions extract myosin heavy- and light-chains, and troponin C from rabbit fibers. This extraction is virtually abolished by TMAO. Natural zwitterions, such as TMAO, have been shown to protect proteins against destabilization by high salt or other denaturatants. Our data indicate that, even in the best of salts, destabilization of the actomyosin complex may play a role in the effect of high ionic strength on the contractile process.

Adenosine Triphosphate↗

PubMed1993

Contraction of developing avian heart muscle.

1. Developmental changes in contraction of chick heart show strong similarities with those of the mammalian myocardium. 2. Normalized twitch force of intact trabeculae from chick left ventricle increases most markedly during the 3-day period around the time of hatching. 3. At any age, elevation of extracellular [Ca2+] to 10-20 mM increases twitch force to a maximum. 4. Studies using membrane-free ("skinned") trabeculae demonstrate that the developmental increase in twitch force is paralleled by an increase in the maximal contractile capability of the muscle, that is probably due to proliferation of contractile proteins. 5. At all ages studied, maximal twitch force of intact trabeculae at 10-20 mM extracellular [Ca2+] is similar to maximal Ca(2+)-activated force of the trabeculae after skinning. 6. Calcium sensitivity of the contractile apparatus in chick heart decreases with development in parallel with isoform switching in troponin T. 7. The depressant effect of acidosis on calcium sensitivity of the contractile apparatus increases with development in parallel with isoform switching in troponin I. 8. As in mammalian heart, both acidosis and inorganic phosphate (Pi) depress force generation by the contractile machinery of chick heart.

Animals↗

PubMed1991

Changes in force and calcium sensitivity in the developing avian heart.

The aim of this study was to characterize the development of the contractile properties of intact and chemically skinned muscle from chicken heart and to compare these characteristics with those of developing mammalian heart reported by others. Small trabeculae were dissected from left ventricles of Arbor Acre chickens between embryonic day 7 and young adulthood (7 weeks post-hatching). At all ages, increasing extracellular calcium (0.45-3.6 mM) progressively increased twitch force of electrically stimulated trabeculae. Twitch force at 1.8 mM extracellular calcium, normalized to cross-sectional area, increased to a maximum at 1 day post-hatching, remained constant through 3 weeks post-hatching, but then decreased at 7 weeks post-hatching. The maximal calcium-activated force of trabeculae chemically skinned with Triton X-100 detergent increased to a maximum 2 days before the time of hatching and was not significantly changed up to 7 weeks post-hatching. Over the ages studied, average twitch force in 1.8 mM calcium was between 26 and 66% of maximal calcium-activated force after skinning, suggesting that the contractile apparatus is not fully activated during the twitch in normal Ringer. In skinned trabeculae, the calcium sensitivity of the contractile apparatus was higher in the embryo than in the young adult. These age-dependent changes in calcium sensitivity are correlated with isoform switching in troponin T. A decrease in pH from 7.0 to 6.5 decreased the calcium sensitivity of the contractile apparatus to a greater degree in skinned trabeculae from young adult hearts than in those from embryonic hearts. This change in susceptibility to acidosis is temporally associated with isoform switching in troponin I.(ABSTRACT TRUNCATED AT 250 WORDS)

Acidosis↗