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Biomedical subjects

A F Martin

Publications and source records attributed to A F Martin.

At least 37 records · Page 2Linked to original sources
PubMed1986

Isomyosin transitions in ventricles of aldosterone-salt hypertensive rats.

The isomyosin composition in left and right ventricles from aldosterone-salt-treated hypertensive rats and from vehicle-infused and aldosterone-infused normotensive control rats was compared. A significant incremental increase (20%) in the percentage of V3 isomyosin and parallel decrease in the percentage of V1 isomyosin occurred in both left and right ventricles from aldosterone-salt-treated animals compared with those in normotensive vehicle-infused controls. No change in the ventricular isomyosin distribution was observed in animals infused with aldosterone without salt, which indicates that aldosterone does not directly affect the ventricular isomyosin composition. The changes in left ventricular isomyosin composition were accompanied by significant left ventricular hypertrophy (38%; p less than 0.05), whereas no hypertrophy was observed in the right ventricle. Plasma thyroxine levels were significantly lower in aldosterone-salt-treated rats (3.7 +/- 0.6 micrograms/dl; p less than 0.05) than in normotensive vehicle-infused (6.0 +/- 0.7 micrograms/dl) or aldosterone-infused (6.7 +/- 0.3 micrograms/dl) controls. These results indicate that factors such as alterations in thyroid status or a volume overload component of this hypertensive model, in addition to increased systolic blood pressure, may contribute to a biventricular shift in isomyosin composition in the aldosterone-salt model of hypertension.

Aldosterone↗
PubMed1986

Differential effects of pH on calcium activation of myofilaments of adult and perinatal dog hearts. Evidence for developmental differences in thin filament regulation.

Our results show that calcium activation of myofilament preparations of dog heart in the perinatal period is unaffected by a reduction in pH from 7.0 to 6.5, which, in adult heart myofilaments, induces a 0.4 pCa unit (-log molar free calcium concentration) rightward shift in the relation between pCa and myofibrillar adenosine triphosphatase activity. Acidic pH also had no effect on calcium binding to myofibrillar troponin C of perinatal hearts. The stoichiometry of troponin C bound calcium at full myofilament activation (about 3 mol calcium/mol troponin C) was the same for adult and perinatal heart myofibrils, as was their myofibrillar troponin C content. Moreover, there were no differences in isoelectric pH of troponin C from adult and perinatal hearts. We tested whether variants of myofilament proteins other than troponin C could account for the differential effects of acidic pH. In adult and perinatal dog heart preparations, myosin heavy chain isoenzymes appeared the same as measured, using native pyrophosphate gel electrophoresis. No evidence for thick filament-related calcium regulation in the perinatal heart myofilaments was obtained, when tested in studies in which native thin filaments were displaced with a 10-fold molar excess of pure actin. In preparations in which native thick filaments were displaced with a 10-fold molar excess of pure skeletal muscle myosin, the effects of acidic pH on calcium activation were the same as in native adult and perinatal preparations. Our major conclusion from these results in that the perinatal heart myofilaments are likely to possess variations in thin filament activity and structure.(ABSTRACT TRUNCATED AT 250 WORDS)

Actin Cytoskeleton↗
PubMed1985

Cardiac myofibrillar creatine kinase is not influenced by hypothyroidism.

The cardiac myofibrillar component of the phosphorylcreatine shuttle mechanism enzymatically couples the functionally significant processes of energy utilization (ATPase) with substrate regeneration by creatine kinase (CK). Both components have isoenzyme forms that are transcriptionally regulated. Propylthiouracil-induced (PTU) hypothyroidism reduced rat cardiac contractile protein ATPase activity by shifting isomyosin predominance from the V1 to the V3 form. However, neither CK specific activity or CK isoenzyme composition was altered by PTU treatment. Thus, myofibrillar components of the phosphorylcreatine shuttle, ATPase and CK, are not coordinately regulated under hypothyroid conditions.

Adenosine Triphosphatases↗
PubMed1985

Isomyosin and thyroid hormone levels in pressure-overloaded weanling and adult rat hearts.

We examined the relationship between ventricular isomyosin composition and plasma thyroxine (T4) 5 wk after partial constriction of the abdominal aorta in weanling (21 day) and adult (8 wk) rats. Cardiac enlargement in weanling aorta-constricted animals was associated with a significant (P less than 0.001) decrease in %V1 isomyosin in both left (32%) and right ventricles (25%) with a corresponding increase in the %V3 isomyosin and a reduction in plasma T4 levels. However, the ratio of V1/T4 was similar in weanling control (17.8 +/- 0.8) and aorta-constricted (18.0 +/- 1.4) rats. In adult aorta-constricted animals, there was a significant (P less than 0.001) reduction in the %V1 (16%) isomyosin in the left ventricle and a smaller decrease in the right ventricular V1 (8%) with no change in plasma T4 levels. There was also a significant difference in V1/T4 between control (16.1 +/- 0.4) and aorta-constricted (13.9 +/- 0.7) adult rats in contrast to the maintenance of the V1/T4 in weanling aorta-constricted animals. Thus both increased workload and changes in thyroxine levels contribute to the isomyosin redistribution seen in weanling rats subjected to a pressure overload, whereas, in adult hypertrophied hearts, alterations of the ventricular isomyosin composition appear to be due solely to the increased pressure overload.

Animals↗
PubMed1984

Isomyosin distribution in skeletal muscles of normal and myotonic goats.

Isoforms of myosin were examined in hindleg muscles isolated from normal and myotonic goats. The muscles studied were the soleus, gastrocnemius, gluteus accessorius, semitendinosus, semimembranosus, and adductor. The isomyosins were analyzed by pyrophosphate polyacrylamide gel electrophoresis. The relative proportions of slow and fast myosin isoforms present were determined by densitometric scanning of Coomassie Blue-stained gels. All muscles contained three fast myosin isoforms and either one or two slow myosin isoforms. In normal goat, the soleus and gastrocnemius, containing 70%-75% slow isomyosins, were representative of slow muscle. The semimembranosus, the semitendinosus, and the adductor, with more than 50% fast myosin, represented a predominantly fast muscle group. The gluteus accessorius, with approximately 45% fast myosin isoforms, was intermediate between the other two groups. In the myotonic goat, a consistent and significant increase in the proportion of fast isomyosins was observed for all the muscles studied. The largest change occurred in the gastrocnemius where the incremental increase in the percentage of fast isomyosins was over 30%. All the other muscles examined had incremental increases in fast isomyosin content which ranged from 16.1% to 22.0%. These results suggest that the abnormal action potential pattern of myotonia leads to a redistribution of the myosin isoforms.

Action Potentials↗
PubMed1984

Perinatal nutritional modification of weanling rat heart contractile protein.

The present study ascertained the influence of litter-size-induced perinatal nutritional modification on cardiac contractile protein enzymatic activity and isomyosin composition. Myofibrillar enzyme activities for Mg2+ -ATPase, Ca2+ -ATPase, and creatine kinase (CK) in the weanling heart were unaltered by nutritional modification. However, these enzyme activities were all significantly augmented in the adult heart. Hill plot analyses of Mg2+ -ATPase activities indicated that myofibrillar calcium regulation was not influenced by either nutritional modification or the weanling-to-adult developmental progression. Isomyosin V1 composition (90 +/- 1%) correlated with plasma thyroid hormone level in normal-growth (8/litter) weanlings. Undernutrition retarded conversion of V3 isomyosin to the V1 species while overnutrition enhanced isomyosin conversion. Isomyosin composition in weanling rats subjected to perinatal nutritional modification was independent of thyroid status. In the adult rat, plasma thyroxine levels were increased, whereas V1 isomyosin remained unchanged (88 +/- 2%) compared with that of the weanling groups. Discrepancies in the relationship between contractile protein enzymatic activities, myosin composition, and heart function are apparent between both the litter-size-adjusted weanling rats and between weanling and adult animals. These discrepancies indicate the complex relationship between heart function and contractile protein properties.

Animals↗
PubMed1981

Turnover of cardiac troponin subunits. Kinetic evidence for a precursor pool of troponin-I.

The turnover of troponin-T, troponin-I, and troponin-C, under conditions closely approximating a steady state, has been determined from the rate of incorporation of L-[4,5-3H]leucine into the polypeptides. Isotope was administered to rats by constant infusion for a period of 4 h and the rate of equilibration of radioactive leucine in the serum was determined. The specific radioactivity of leucine was measured in both the protein and the precursor pools. Troponin subunits were separated from other proteins by polyacrylamide gel electrophoresis. The turnover rates of other myofibrillar proteins, tropomyosin, actin, and myosin heavy and light chains, were also measured. Troponin-T and troponin-I had similar half-lives of 3.5 and 3.2 days, respectively, which were significantly different from that of troponin-C (5.3 days). The rates of turnover of troponin-T and troponin-I were greater than those of myosin heavy chain, but the turnover of troponin-C was not significantly different from that of myosin heavy chain. These findings indicate that the subunits of cardiac troponin turn over nonuniformly. In addition, evidence from kinetic experiments indicates the presence of a precursor pool of unassembled troponin-I but not for troponin-T or troponin-C.

Animals↗
PubMed1980

The selective adherence of lymphoblasts to antigenic cell monolayers. A method for determining the specificity of lymphocytes proliferating in response to histocompatibility antigens.

The specificity and intensity of the immune response of rat lymph nodes draining a skin allograft were examined by exploiting a monolayer of donor-type thoracic duct lymphocytes as an immunoabsorbent. Stable monolayers were produced by attaching lymphocytes from different strains of rat to Petri dishes pretreated with poly-L-lysine. The responding lymph node cells were labelled in vitro with [3H]Thymidine, incubated on the monolayer and mechanically separated into non-adherent and adherent fractions. The radioactivity associated with the adherent fraction was 7--8 times greater when the monolayer displayed the immunizing major histocompatibility antigens than when syngeneic or 'third party' monolayers were used. The non-specific adherence to syngeneic monolayers was low and consistent. Immunization to minor histocompatibility antigens may also be studied by this method.

Adsorption↗
PubMed1977

Measurements of half-life of rat cardiac myosin heavy chain with leucyl-tRNA used as precursor pool.

The kinetics of labeling of myosin heavy chain, following a single intravenous injection of L-[4,5-3H]leucine, were analyzed with the help of a computer, in conjunction with the labeling kinetics of the specific radioactivities of the precursor amino acid pool. As precursor we used leucyl-tRNA which, as we show here, differs significantly from the intracellular free leucine pool. The half-life of myosin heavy chain was determined from the initial period (0 to 60 min) of incorporation of label into protein after a single injection of tritiated leucine, and also from the period (7 to 14 days) when there is exponential decay of the labeled protein. Myosin heavy chain was separated from other myofibrillar proteins by polyacrylamide gel electrophoresis before measurement of leucine specific radioactivity. The specific radioactivity was measured in both protein and precursor pools by a sensitive isotope dilution procedure (range, 100 to 1500 pmol). The values for the half-life of myosin heavy chain determined at both intervals were similar (5.4 and 5.9 days). Substitution of the specific radioactivity of the intracellular free leucine pool decreased the half-life to 2.7 dyas. Similar values were obtained when the half-life was calculated by simple graphical integration of the experimental curves.

Amino Acids↗
PubMed1976

Control of protein balance in hypertrophied cardiac muscle.

The levels of intracellular proteins are determined by a balance between their rates of synthesis and degradation. During the development of regression of cardiac hypertrophy, both of these rates can be expected to change. Possible control sites of synthetic and degradation processes are discussed in this article. The following experimental results are presented: (1) Cardiac mitochondrial cytochromes accumulate early after imposition of pressure overload, as a result of an increased rate of synthesis and decreased rate of degradation. (2) The half-life of myosin heavy chains (HC) in the steady state was determined from incorporation kinetics, using leucyl-tRNA as precursor, to be 5-6 days. (3) The existence of a pool of newly synthesized myofilaments which are not fully incorporated into the core of myofibrils is indicated by the incorporation data.

Animals↗