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Biomedical subjects

U N Singh

Publications and source records attributed to U N Singh.

At least 19 recordsLinked to original sources

Intercellular communication in rapidly proliferating and differentiated C6 glioma cells in culture.

Glial cells in the brain are known to provide structural and functional supports to neurons. To sustain such a supportive role, they have developed cell-to-cell communicating gap junctional channels. The authors studied the effect of dbcAMP on gap junctional channels mediated communication in C6 cells, a rat glioma cell line. Quantitative assessment of coupled cells under microscope after microinjection of a fluorescent dye was taken as a measure of junctional permeability. An enhanced coupling between cells was observed following dbcAMP treatment and this elevated coupling was found to be dependent on the duration of exposure of cells to dbcAMP. The studies have focused on a subtle shift in the spatial organization of the functional channels to the processes of dbcAMP induced differentiated cells from the cell cytoplasms and membranes of dbcAMP untreated cells. Immunofluorescence study with affinity purified antibody against gap junction further confirmed the spatial distribution of gap junctional protein(s) in the processes and also showed an increase in the density of the protein at the intercellular spaces in dbcAMP induced differentiated C6 glioma cells.

Animals↗

Polyribosome dynamics: size-distribution as a function of attachment, translocation and release of ribosomes.

Assembly of polyribosomes is the ubiquitous manifestation of the activation of translational machinery in cells. This is accompanied by a concomitant appearance of mRNAs either from an activation of pre-existing ribo-nucleoprotein particles (RNP) or from newly synthesized transcripts. The size-distributions of polyribosomes as inferred from their sedimentation profiles are essentially defined by various kinetic parameters responsible for continuous flux of ribosomes due to their recycling between the "free" and the "bound" states. In the theoretical analysis presented here the time-evolution of polyribosomes and their sustenance in the steady state is considered as a Markovian process with the states of mRNAs defined as the number of ribosomes attached. Expressions for the elements of one-step transition matrix as a function of kinetic parameters related to the initiation, translocation and the release of ribosomes and the size of mRNA are derived. The latter is shown to be relevant only in so far as it sets an upper limit to the size of polyribosomes. Implications of transient arrest of ribosomes at the initiation site as envisaged in the signal hypothesis for the synthesis of secretory proteins and the putative role of receptor-mediated post-translational transport of proteins have been examined. Results of computer simulations on model systems have focussed attention on the diverse types of profiles that may appear under varying physiological conditions.

Animals↗

Studies on functioning of reconstituted gap junctional channels.

We examine the functioning of isolated rat liver gap junction protein after reconstituting into unilamellar liposomes with the help of fluorescence-efflux assay. Monitoring of the dequenching of a fluorescence marker 5, (6) CF due to its efflux from proteoliposomes into extra-liposomal space via its passage through reconstituted gap junctional channels has been performed. The efflux of dye from intra-liposomal to extra-liposomal compartment (both final release or Feq and initial rate or IR) was found dependent on gap junction concentrations. The opening and closing of reconstituted gap junctional channels were found influenced by pH and osmolarity of the extra-liposomal solution.

Animals↗

A device for transplantation of single cells.

A device with a high degree of precision is described for the transplantation of single identified cells in specified regions of the host brain. It consists of two co-centric micropipettes where the inner pipette, functioning as a plunger, is used to drive the cells contained near the tip of the outer pipette into the host. The use of a pre-calibrated micrometer to control the movement of the inner pipette obviates the need of visual monitoring for successful transplantation.

Animals↗

Liposome shrinkage and swelling under osmotic-diffusional stress: evaluation of kinetic parameters from spectrophotometric measurements.

Analyses of spectrophotometric measurements of shrinkage and swelling of liposomes under osmotic-diffusional stress tacitly assume an 'empirical' inverse relationship between the absorbance (A) and the liposomal volume (v). In this paper, we have proposed an alternate more explicit relationship: A = EcL e - alpha Lv/1-Lv where L is liposomal concentration, Ec the extinction coefficient and alpha a dimensionless parameter. The exponential term, in essence, defines the partitioning of aqueous volume into intra- and extra-liposomal compartments. Experimental data obtained with glycerol as model compound are used to test the validity and internal consistency of the proposed formalism.

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