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Biomedical subjects

L A Bourret

Publications and source records attributed to L A Bourret.

8 recordsLinked to original sources
PubMed1978

DNA synthesis in cartilage cells is stimulated by oscillating electric fields.

External oscillating electric fields (1166 volts per centimeter, 5 hertz) enhanced the incorporation of [3H] thymidine into the DNA of chondrocytes isolated from the proliferative layer of embryonic (16 days) chick epiphysis. Verapamil or tetrodotoxin at 10(-6)M concentrations completely blocked the electric field effect. Tetracaine reduced the incorporation of [3H] thymidine in both control and electrically stimulated cells. The findings support the hypothesis that Na and Ca2 fluxes generated by the electrical perturbation trigger DNA synthesis in these cells.

Animals↗
PubMed1977

Membrane changes during cartilage maturation. Increase in 5'-nucleotidase and decrease in adenosine inhibition of adenylate cyclase.

To examine the potential participation of the plasma membrane in differentiation, we studied the enzymatic activities of 5'-nucleotidase and adenylate cyclase as a function of chondrocyte maturation. 16-day-old chick embryo tibiae epiphyses were dissected into proliferative, growing and hypertrophying zones. Partially purified membrane fractions prepared by differential centrifugation from the respective tissue segments were assayed for enzymatic activity. Cell suspensions from the same segments were examined cytochemically for the presence of 5'-nucleotidase. The findings show that the 5'-nucleotidase activity of the chick embryo epiphyseal cartilage has the following characteristics: (a) it has a Km of about 25 muM for 5'AMP, and is inhibited by a mixture of 2' and 3'AMP (apparent Ki about 10(-4) M) and by AOPCP; (b) it is predominantly localized at the cell surface but is also detected in the cytoplasm and in association with nuclear heterochromatin; and (c) it increases 10-fold (on a DNA basis) during the maturation of the epiphyseal cartilage cells. The adenylate cyclase activity has these characteristics: (a) it does not change during chondrocyte maturation (on a DNA basis); (b) its susceptibility to adenosine inhibition decreases at least 10-fold. The implication of these findings relative to a possible role of adenosine in cellular communication is discussed.

Adenosine↗
PubMed1977

Epiphyseal cartilage cAMP changes produced by electrical and mechanical perturbations.

Epiphyseal cartilage from chick embryo was subjected in vitro for one to 15 minutes to static compressive forces or oscillating electric fields. The same stimuli were applied to suspensions of cells isolated from the epiphyses. At the end of the perturbation cAMP was measured in the tissue or cell extracts by radioimmunoassay. It was found that a physiological (60 g/cm2) static pressure reduced the cAMP content in the tissue and the separated cells. An oscillating electric field above 900 V/1.5 cm, 5Hz, enhanced the cAMP accumulation in the intact tissue. This effect was produced only when the long axis of the bones was oriented parallel to the electric field. In isolated cells an electric field above 750 V/1.5 cm, 5Hz, caused a decrease in cAMP content. Charged matrix macromolecules and orientation of the cells within the cell matrix may have a modulating effect on the initiation of this response. It is postulated that the change in cAMP is the early cellular signal in the response to an electrical or mechanical perturbation which leads to bone remodeling.

Animals↗
PubMed1976

The role of calcium in the inhibition of cAMP accumulation in epiphyseal cartilage cells exposed to physiological pressure.

A hydrostatic pressure of 60g/cm sq (0.85 psi) inhibits the accumulation of cAMP in cells isolated from the proliferative zone of chick-tibia epiphyseal cartilage. The following findings indicate that this effect is mediated by a translocation of calcium: (i) the pressure enhances the cellular uptake of radiocalcium; (ii) the pressure effect on cAMP can be simulated by the calcium-ionophore A23187; (iii) the effects of pressure and A23187 are non-additive; (iv) the pressure effect is not produced in the presence of ethylenebis-(oxyethylenenitrilo)-pressure effect is not produced in the presence of ethylenebis-(oxyethylenenitrilo)-tetraacetic-acid (EGTA); (v) the particulate adenyl cyclase activity of the proliferative zone is susceptible to non-competitive calcium inhibition. Throughout this study cells from the hypertrophic zone of the same epiphyses were used as controls. In these cells the calcium uptake was enhanced by pressure, but the cAMP level was not affected by pressure, A23187 or EGTA. This change in responsiveness, which accompanies the maturation of the cartilage cells, was shown to be due to a decrease in the calcium-inhibition of adenylate cyclase.

Adenylyl Cyclases↗
PubMed1975

Cyclic AMP and cyclic GMP: mediators of the mechanical effects on bone remodeling.

Compressive forces of physiological magnitude (60 grams per square centimeter) reduce the adenosine 3',5'-monophosphate and guanosine 3',5'-monophosphate content of the epiphyses of tibiae from 16-day-old chick embryos. An equivalent hydrostatic pressure applied directly to cells isolated from this tissue also affects cyclic nucleotide accumulation. The tissue response is uniform throughout the epiphysis, whereas the cell response varies according to the area of origin.

Animals↗