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Biomedical subjects

M Fry

Publications and source records attributed to M Fry.

At least 109 records · Page 6Linked to original sources
PubMed1979

Replicative activity of isolated chromatin from proliferating and quiescent early passage and aging cultured mouse cells.

Replicative activity of isolated chromatin from late passage cultured mouse cells has been compared to the activities of chromatin preparaions from dividing and quiescent early passage cells. Rates of endogenous DNA synthesis are similar for chromatin from growing or resting cells but this activity is stimulated 2.5-fold in senescent cell chromatin. Chromatin from growing young cells copies exogenously added single stranded DNA at the highest efficiency. Chromatin of senescent cells copies this template at a lower rate and resting young cell chromatin replicates single stranded DNA at the lowest efficiency. Similar relative rates are obtained when activated DNA is copied by the various chromatin preparations. Total activity of DNA polymerase extracted by salt from chromatin is similar for dividing and quiescent young cells but the proportion of DNA polymerase beta is higher in the latter. Elevated activities of DNA polymerases are extracted from chromatin of old cells. It is concluded, therefore, that chromatin-directed replication is differently arrested in non-dividing senescent cells and in quiescent early passage cells. The possible regulatory mechanisms of DNA replication in quiescence and aging are discussed.

Age Factors↗
PubMed1979

The effect of cephaloridine on the stability of rat kidney lysosomes.

The administration of cephaloridine to rats caused a decrease in the excretion of acid phosphatase into the urine. The antibiotic itself had no effect on urinary acid phosphatase and inhibitors or proteolytic enzymes were not present in the urine from treated rats. Cephaloridine may therefore be stabilizing the lysosomal membrane in vivo and experiments with isolated lysosomes confirm this hypothesis. The lysosomal integrity was followed by measuring the acid phosphatase activity and the light scattering properties of the particles. A good correlation was obtained between these parameters in the case of thermal disruption and progesterone induced lysis of the lysosomes and low concentrations of cephaloridine (0.1-1.0 mmol/1) protected the lysosomes against this form of damage.

Acid Phosphatase↗
PubMed1979

The monitoring of lysosomal integrity by pH-stat and light scattering measurements.

Light scattering measurements were used to monitor the integrity of isolated rat kidney lysosomes during prolonged incubation at 37 degrees C or following the addition of lysolecithin. The fall in extinction at 520 nm (E520) was shown to correlate very well with the fall in the particulate enzyme activity and the corresponding rise in the soluble enzyme activity. Measurements were also made of the release of H+ from the lysosomes into the suspending medium following treatment with lysolecithin. A good relationship was obtained between acidification of the medium and changes in the light scattering (E520) of the lysosomal suspension. The value of these techniques in following rapid changes in the integrity of lysosomes is discussed.

Animals↗
PubMed1979

The interaction of cephaloridine with model membrane systems and rat kidney lysosomes.

The antibiotic cephaloridine has been shown to interact with phospholipid structures, using the techniques of ultraviolet difference spectroscopy, surface pressure measurements and liposome models. The results indicate that this interaction is at least partly hydrophobic in nature and help explain the disruptive effects of high concentrations of cephaloridine on both artificial and natural phospholipid structures (lysosomes). Low concentrations of cephaloridine were shown to inhibit a lysosomal membrane-bound phospholipase 2 and it is suggested that such an inhibition may explain the cephaloridine-induced stabilization of rat-kidney lysosomes.

Animals↗
PubMed1979

Ion-channel component of cytochrome oxidase.

Cytochrome oxidase is resolvable into an electron transfer complex and an ion transfer complex. The ion transfer complex has been shown to have the capability for inducing nonspecific ion transport into liposomes. Subunit I of cytochrome oxidase has been identified as an ion-channel-forming protein.

Biological Transport, Active↗
PubMed1979

Sarcomere motion in isolated cardiac cells.

Computerized image-analysis techniques have been employed to examine the sarcomere dynamics of isolated mammalian cardiac myocytes. The cells were prepared by perfusion of adult rabbit hearts with hyaluronidase-collagenase solutions; they exhibited phasic contractions in the presence of 10(-6) M Ca2+. The dissociated cells were visualized by phase microscopy and a video camera interfaced in a minicomputer. Digitized cell images were processed by an algorithm utilizing signal averaging and contrast enhancement to yield data showing individual sarcomere position and shortening vs. time, so that patterns of sarcomere activation could be observed in spontaneously contracting cells. Compared to records of whole-cell shortening and of striation displacement, computerized image analysis provided a much more faithful indication of time course and sequence of sarcomere shortening. Spontaneously contracting cells showed sequential sarcomere shortening beginning at one end and propagating longitudinally with a constant velocity, typically at 100--150 micron/s for beat rates of 40 min-1. Velocities of initial sarcomere shortening appeared to increase with elevated Ca2+. These observations are consistent with a regenerative mechanism of calcium-induced calcium release.

Animals↗
PubMed1978

Protein turnover in senescent cultured chick embryo fibroblasts.

The over-all rates of protein synthesis, degradation and net accumulation were estimated in rapidly growing young and slowly doubling old cultures of chick fibroblasts. We find that not only the rate of protein synthesis is reduced in senescent cultures, but the average rate of protein degradation is also slowed down considerably. This decrease in the rate of protein breakdown in aging cells stands in contrast with the previously observed acceleration of this process by other conditions (such as serum deprivation or overcrowding) that lead to the cessation of cellular growth. Though the retarded protein degradation may contribute to the acculation of abnormal proteins in senescent cells we find that the breakdown of grossly abnormal puromycin peptides proceeds equally rapidly in young and old cultures. The protein content of senescent cells increases by 1.8-fold as compared to young cells, while the average cell volume is increased even more (almost 5-fold). By contrast, consideration of the over-all balance of protein metabolism in these cells indicates that the average concentration of metabolically turning-over proteins is somewhat higher in senescent than in young fibroblasts.

Cell Count↗
PubMed1978

Resolution of complex III of the mitochondrial electron transfer chain into two component complexes.

Complex III can be resolved into an electron transfer complex and an ion transfer complex. The electron transfer complex contains exclusively the oxidation-reduction proteins of complex III, and the ion transfer complex the capability for augmenting cation-induced fluorescence of 8-anilino-1-naphthalenesulfonic acid. This finding has important implications for the molecular mechanism of mitochondrial energy coupling.

Animals↗
PubMed1978

Resolution of cytochrome oxidase into two component complexes.

Cytochrome c oxidase (ferrocytochrome c: oxygen oxidoreductase, EC 1.9.3.1) has been resolved into a pair of complexes of unequal molecular weight. The larger complex (electron transfer complex) contains exclusively the oxidation-reduction proteins characteristic of cytochrome oxidase; the smaller complex (ion transfer complex) shows exclusively the capability for cation-dependent induction of the fluorescence of 8-anilino-1-naphthalenesulfonic acid--a capability demonstrable in preparations of cytochrome oxidase. The duplex nature of cytochrome oxidase has important implications for the mechanism of energy coupling.

Copper↗
PubMed1978

Highly efficient copying of single-stranded DNA by eukaryotic cell chromatin.

Chromatin prepared from S phase hepatoma tissue culture (HTC) cell incorporates in vitro about 11-14 pmoles [3H]dTMP into DNA in 30 min. Single-stranded DNA added to this chromatin stimulates DNA synthesis more than 40-fold whereas activated DNA enhances it about 60-fold. By contrast, stimulation of DNA synthesis by activated DNA in a crude nuclear extract exceeds the stimulation exerted by denatured DNA by a factor of 7. Stimulation of DNA synthesis by denatured DNA is not due to stabilization of either the chromatin or the product of the endogenous reaction. On the other hand, we find that poly(dC) and poly (dT) enhance DNA synthesis by serving as templates which are copied by chromatin in a true complementary fashion. It seems therefore, that eukaryotic cell chromatin is able to copy single-stranded DNA at a high efficiency. Chromatin of G1 arrested cell copies exogenous templates at a considerably reduced rate. The enzyme responsible for the copying of denatured DNA is tentatively identified as DNA polymerase alpha on the basis of its sensitivity to sulfhydril group blocking, its requirements for ions and failure to copy the ribo strand of oligo(dT) poly(A).

Adenosine Triphosphate↗
PubMed1977

Surface proteins of young and senescent cultured avian fibroblasts.

Proliferation of senescent cultured chick fibroblasts is arrested at densities that are 3-4 fold lower than densities inhibiting growth of young cells. The effects of density and growth rate of young and aged cultures on the accessibility of their surface proteins to external iodination were studied. LETS glycoprotein and a protein of 110,000 daltons are the major iodinated proteins of resting, highly dense and of sparse young cells, respectively. By contrast, LETS is minimally exposed on undividing, relatively disperse old cells. Therefore, exposure of LETS is correlated with cell density rather than with growth rate.

Cell Count↗
PubMed1976

Altered nuclear deoxyribonucleic acid alpha-polymerases in senescent cultured chick embryo fibroblasts.

DNA alpha-polymerase has been partially purified from nuclei of cultured chic, fibroblasts and separated on phosphocellulose columns into two distinct activities designated DNA polymerases alpha(a) and alpha(b), respectively. The enzyme preparations were devoid of activities of DNA beta,gamma-polymerases terminal deoxyribonucleoside transferase, DNase, DNA-dependent RNA polymerase, and phosphatase. DNA polymerases alpha(a) and alpha(b) both having molecular weights of 160 000, constitute 35-50 and 65-50%, respectively, of the activity of alpha-polymerase in the nucleus. These enzymes differ in their requirements for maximal activity, their relative ability to copy oligo(dG)-poly(dC), their response to ribonucleoside triphosphates, and their kinetics of heat inactivation. When the properties of alpha polymerases derived from early or late passage cultures have been compared, no difference could be detected as a function of cell age in the specific activities of the polymerases in crude cell extracts, their chromatographic behavior on diethylaminoethylcellulose and phosphocellulose columns, and their relative abilities to utilize single deoxyribonucleoside triphosphates with activated DNA template. On the other hand, both enzymes become partially heat labile in aging cells. Also, the activity of DNA polymerase alpha(a) from young cells was stimulated by 2--10 mM adenosine or cytidine triphosphates, whereas the same enzyme from old cultures was inhibited by these agents. Conversely, these ribonucleoside triphosphates inhibited the activity of polymerase alpha(b) in young cells but slightly stimulated this enzyme derived from senescent fibroblasts. In addition, the relative ability of DNA polymerase alpha(a) to copy oligo(dG)-poly(dC) decreased in aged cells, whereas that of DNA polymerase alpha(b) increased. We have also observed significant differences in the effects of potassium chloride and N-ethylmaleimide on the activity of DNA polymerase alpha(a) from old cells as compared to young cells. These age-related alterations in the properties of the two avian DNA polymerases may reflect structural or conformational changes in these enzymes.

Adenosine Triphosphate↗
PubMed1976

The effect of dietary sodium chloride on blood pressure, body fluids, electrolytes, renal function, and serum lipids of normotensive man.

Eight normotensive white middle-aged men were given low, moderate, and high salt diets with constant potassium intakes each for periods of at least 4 weeks. There was a tendency for body weight, serum sodium, exchangeable sodium, and inulin space to increase. Indirect blood pressure measurements revealed no change in blood pressure, either supine or upright measurements, during the 3 study intervals. Inulin clearance (and presumably glomerular filtration rate) rose with increase in dietary salt. Urinary potassium excretion rose progressively as salt intake increased. Total body potassium tended to decrease with increase in dietary salt. There was no changes in the excretion of calcium, magnesium, phosphorus, nor were there changes in the blood level of potassium. There was no change in total body water. The serum cholesterol and triglyceride levels were not appreciably affected by the different dietary sodium intakes. Plasma renin activity and urinary aldosterone excretion rose progressively with the two levels of sodium restriction. These studies indicate that normal man is able to compensate for large differences in sodium intake with minor metabolic changes. These changes do not necessarily lead to hypertension over a one-month period. Nevertheless, many hemodynamic and hormonal compensatory mechanisms come into play. It is evident that hypertension might result should the sodium load not be excreted, the circulating volume become too great for the excretory capacity, or if neural or endocrine adjustments be inadequate.

Adult↗