Biomedical subjects

R L Tellam

Publications and source records attributed to R L Tellam.

41 records · Page 3Linked to original sources

PubMed1985

The free cytoplasmic calcium concentration of tumorigenic and non-tumorigenic human somatic cell hybrids.

The fluorescent indicator of Ca2+ concentration, quin-2, has been used to measure the concentration of free Ca2+ in the cytoplasm of tumorigenic and non-tumorigenic human somatic cell hybrids. The cell hybrids were derived from the fusion of a HeLa derivative (D98 AH2) and normal human fibroblasts. The calcium concentration of the tumorigenic cell lines was 180 +/- 7nM and the level in the non-tumorigenic cells was 136 +/- 6nM. This difference was statistically highly significant (P less than 0.001). Control experiments are reported which show that the level of 3a2+ measured is not influenced by cell density or by the concentration of quin-2-tetra-(acetoxymethyl)ester used in these experiments. The possible implications of this elevated level of cytoplasmic calcium in tumorigenic cells are discussed.

Aminoquinolines↗

PubMed1985

Actin synthesis in tumorigenic and non-tumorigenic human hybrid cells.

We have previously shown that the total actin content of tumorigenic HeLa/fibroblast somatic cell hybrids is significantly lower than that of the non-tumorigenic hybrid cells. A measure of actin synthesis, relative to total protein synthesis, was obtained for these cells to determine whether the reduced actin content of the tumorigenic cells is due to specific suppression of actin synthesis. Actin synthesis was measured in cells labelled with [35S]methionine using DNase I affinity chromatography to isolate the actin quantitatively. The results show that actin synthesis is not specifically suppressed, since the relative amount of actin synthesized is constant for the tumorigenic and non-tumorigenic cell lines. The reduced actin content of the tumorigenic cells is therefore most likely to be the result of increased degradation of actin.

Actins↗

PubMed1984

The binding of Ca2+ to actin monomer is monitored by the fluorescence of actin-bound auramine O.

The fluorescence of the cation auramine O was substantially enhanced by the presence of actin monomer. Titrations of this fluorescence enhancement indicated that actin monomer had two auramine O binding sites, each with a dissociation constant of approx. 20 microM. Calcium ions had no effect on the number of actin monomer-bound auramine O molecules or on the dissociation constant for that interaction. However, calcium ions increased the maximum change of fluorescence that occurs when actin monomer was fully saturated with auramine O. This effect of calcium was saturable and yielded a Ca2+ dissociation constant of 1.6 mM. It was concluded that auramine O bound to sites on actin monomer and independently monitored the binding of Ca2+ ion(s) to other site(s) on actin monomer. Further, the magnitude of the Ca2+ dissociation constant suggested that this Ca2+-binding site may be representative of the multiple bivalent cation-binding sites on actin monomer which are thought to be directly involved in actin polymerization. However, the exact relationship between these sites remains unclear.

Actins↗

PubMed1984

Microfilament organization and total actin content are decreased in hybrids derived from the fusion of HeLa cells with human fibroblasts.

The organization of the microfilaments and the actin content of matched pairs of tumorigenic and non-tumorigenic HeLa/fibroblast hybrid cells was compared. Each pair consisted of a hybrid cell line with suppressed tumorigenicity and a segregant tumorigenic cell line derived from it. The tumorigenic HeLa parent cell line and a non-tumorigenic human fibroblast line were also included in the comparison. Microfilament organization of the cell lines was assessed by fluorescence microscopy using NBD-phallacidin, a probe that specifically binds to actin filaments. The re-expression of tumorigenicity is associated with a loss of microfilament organization. The actin content, as measured by the DNase I inhibition assay, was significantly lower in the tumorigenic hybrids and the HeLa parent than in the non-tumorigenic cells. The comparison was significant when the actin concentration was expressed either per cell or per protein. Despite this reduced level of total actin in tumorigenic cells, the ratio of monomeric to total actin remained constant in all cell lines tested.

Actins↗

PubMed1983

The influence of poly(ethylene glycol) 6000 on the properties of skeletal-muscle actin.

Poly(ethylene glycol) 6000 affected many of the properties of skeletal-muscle actin. It accelerated the rate and increased the extent of actin polymerization as measured by light-scattering and sedimentation studies respectively. Moreover, intrinsic-fluorescence measurements showed that addition of poly(ethylene glycol) 6000 decreased the rate of EDTA-induced denaturation of actin monomer and increased the temperature at which irreversible conformational changes occur in actin monomer. These effects occurred without any apparent direct binding interaction and are postulated to be a consequence of the effect of excluded volume on the thermodynamic activity of actin. A relationship based on spherical geometry was formulated which described the co-volume increment that occurs upon addition of a monomer to a long linear polymer in the presence of a space-filling macromolecule. The application of this relationship to the poly(ethylene glycol) 6000-actin system was not without assumption, but it permitted quantitative estimation of the co-volume increment which proved to be of the sign and magnitude required to explain the increased extent of actin polymerization found experimentally in the presence of various concentrations of poly(ethylene glycol) 6000. It is suggested that, in vivo, excluded volume may play a role in actin-filament formation and in the maintenance of the native G-actin structure.

Actins↗