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Biomedical subjects

P Todd

Publications and source records attributed to P Todd.

151 records · Page 9Linked to original sources
PubMedDate not supplied

Electrokinetic isolation of vesicles and ribosomes derived from Serratia marcescens.

Ribosomes and vesicles derived from the bacterium Serratia marcescens were separated from each other and from solubles using density gradient electrophoresis. Transport relationships were used to determine the electrophoretic mobilities of the particles. The effects of convection, sedimentation and diffusion were found to be negligible. The electrophoretic mobility obtained for the ribosome peak is -7 x 10(-5) cm2/(V.s). Under appropriate conditions, two vesicles peaks were obtained, the first with a mobility of -4 x 10(-5) cm2/(V.s) and the second with -9 x 10(-6) cm2/(V.s). This information can be used to predict the resolution of the separands in large-scale electrophoretic separations.

Electrophoresis↗
PubMedDate not supplied

Viable cell recycle with an inclined settler in the perfusion culture of suspended recombinant Chinese hamster ovary cells.

The perfusion culture of suspended mammalian cells requires a cell retention device, the best of which will retain all viable cells and reject all nonviable cells and debris. The inclined settler is a passive, simple, inexpensive, and easy-to-maintain device that has been shown in the past to selectively remove single nonviable cells of hybridoma cultures. In this work, we have demonstrated the preferential return of viable recombinant Chinese hamster ovary (CHO) cells through the use of a three-port settler maintained at lower temperatures and vibrated to reduce cell attachment and enhance cell return to the bioreactor. The residence time of CHO cells in the cooled, vibrated settler was determined by flow-cytometric discrimination of tracer recombinant CHO cells. Cells returning to the bioreactor through the underflow had an average residence time of 1.46 h in the settler. During perfusion cultures with cell densities above 10(6) cells/mL, cells seen to be stalled within the settler were easily dislodged by periodic air bubbling using a simple back-flushing procedure in which headspace gas was brought through the settler underflow port. The resuspended cells were returned to the bioreactor within an average of 32 min after bubbling. This study demonstrates that inclined sedimentation technology can be utilized to selectively recycle viable recombinant CHO cells with only a short retention time in an inclined settler.

Animals↗
PubMedDate not supplied

Growth and induction kinetics of inducible and autoinducible expression of heterologous protein in suspension cultures of recombinant mouse L cell lines.

Mouse Ltk- cells were transfected with four different plasmids for autoinducible and highly-inducible expression of the bacterial lacZ gene and cultivated in suspension. Two selection genes, thymidine kinase (tk) and neomycin resistance (neor), were used to select the clones in both cell lines. The resulting two cell lines, designated M4 and R2, differ in that the inducible MMTV promoter from mouse mammary tumor virus (MMTV) controls glucocorticoid receptor (gr) gene and lacZ gene expression in the M4 cell line ("autoinducible"), while the constitutive rous sarcoma virus (RSV) promoter controls gr gene expression and the MMTV promoter controls lacZ gene expression in the R2 cell line ("highly-inducible"). Both cell lines were stable with respect to reproducibility of growth rate in spinner flasks and inducibility of beta-galactosidase expression. The exponential growth rate of R2 cells was slower than that of M4 cells before induction because the R2 cell line continuously expressed gr genes under the constitutive RSV promoter, and the percent reduction of exponential growth rate mainly caused by gr gene expression was about 20%. The inducibility of the M4 cell line was greater than that of the R2 cell line because in the M4 cell line MMTV promoter controlled gr and lacZ gene expression autoinducibly. Maximum induction of the M4 cell line occurred after induction with the hormone dexamethasone (Dex) at 10(-7) M, and the final beta-galactosidase content increased 400-fold after induction. The optimum conditions for inducer concentration and induction time were determined, and the highest production of beta-galactosidase occurred when Dex was added after the cell concentration had reached its maximum in batch culture. Dex (10(-9) M) is a critical inducer concentration in view of inducibility between M4 and R2 cell lines. The inducibility of R2 cell line is higher than that of the M4 cell line from 0 to 10(-9) M Dex, but the inducibility of M4 was higher than that of the R2 cell line at Dex concentrations of more than 10(-9) M.

Animals↗
PubMedDate not supplied

The use of percent volume analysis in Coulter sizing of cells in gynecologic cytopathologic cell suspensions.

The Coulter Counter model TA II was evaluated as a gynecologic cytodiagnostic tool. The instrument produces particle size histograms as plots of percent volume versus particle volume in 16 channels with each channel corresponding to twice the volume of the next lower channel. Cell volume distributions were obtained using cell suspensions from patients with cervicitis, inflammation, dysplasia or carcinoma and were compared with those from normal subjects. Although this method is superior to other methods of volume distribution analysis, it does not satisfy the stringent requirements of a cervical cancer mass screening method.

Cell Count↗