Importance of oscillations in alveolar gas concentrations in the analysis of rebreathing data

Cyclic rebreathing of a soluble inert gas can be used to estimate lung tissue volume (Vt) and pulmonary blood flow (Qc). A recently proposed method for analyzing such cyclic data (Respir. Physiol. 48: 255-279, 1982) mathematically assumes that ventilation is a continuous process. However, neglecting the cyclic nature of ventilation may prevent the accurate estimation of Vt and Qc. We evaluated this possibility by simulating the uptake of soluble inert gases during rebreathing using a cyclic model of gas exchange. Under cyclic uptake conditions alveolar gases follow an oscillating time course, because gas concentrations tend to increase during inspiration and to decrease during expiration. We found that neglecting these alveolar gas oscillations leads to the underestimation of soluble gas uptake by blood, particularly during the early rebreathing breaths. When continuous ventilation is assumed Vt and Qc are overestimated unless rapid rebreathing rates, large tidal volumes, and gases of moderately low solubility are used. Under these conditions the amplitude of the cyclic oscillations is minimized, the alveolar time course more closely resembles that expected from continuous ventilation, and the resulting errors are minimized. Alternatively, when the effect of oscillating alveolar gas concentrations on mass transfer are considered, these estimation errors can be eliminated without restricting rebreathing rate or gas solubility. We conclude that failure to consider the effect of cyclic rebreathing on the time course of alveolar gas concentrations may result in significant errors when evaluating rebreathing data for Vt and Qc.     

The growth response of cells in medium made hyperosmolal with electrolytes or mannitol.

A comparison of the growth rates of established human lymphoid and tumor cell lines was performed in nutrient medium made hyperosmolal with mannitol, NaCl, or mixtures of NaCl and KCl at a constant Na/K ratio. It was found that considerably higher osmolalities were attained with mannitol than electrolytes before a reduction in the growth rate of the culture was observed. This suggests that mannitol and electrolytes affected the growth rate through different mechanisms. Mannitol uptake was studied with two of the cell lines and both cell lines were found to be permeable to mannitol. This eventually would have eliminated the osmolality gradient between the interior of the cell and the medium, and could explain why higher osmolalities were obtained with mannitol before the growth rate was effected. In addition, initial experiments showed that these cell lines may also be able to metabolize mannitol.     

Interspecies chimeric conditions affect the developmental rate of human pluripotent stem cells

Human pluripotent stem cells hold significant promise for regenerative medicine. However, long differentiation protocols and immature characteristics of stem cell-derived cell types remain challenges to the development of many therapeutic applications. In contrast to the slow differentiation of human stem cells in vitro that mirrors a nine-month gestation period, mouse stem cells develop according to a much faster three-week gestation timeline. Here, we tested if co-differentiation with mouse pluripotent stem cells could accelerate the differentiation speed of human embryonic stem cells. Following a six-week RNA-sequencing time course of neural differentiation, we identified 929 human genes that were upregulated earlier and 535 genes that exhibited earlier peaked expression profiles in chimeric cell cultures than in human cell cultures alone. Genes with accelerated upregulation were significantly enriched in Gene Ontology terms associated with neurogenesis, neuron differentiation and maturation, and synapse signaling. Moreover, chimeric mixed samples correlated with in utero human embryonic samples earlier than human cells alone, and acceleration was dose-dependent on human-mouse co-culture ratios. The altered gene expression patterns and developmental rates described in this report have implications for accelerating human stem cell differentiation and the use of interspecies chimeric embryos in developing human organs for transplantation.     

Isoelectric focusing in polyacrylamide gel using buffer electrode solutions.

Isoelectric focusing in ampholytes of pH 6–8 range has been carried out in polyacrylamide gels using ammonia buffer at pH 10.0 and acetate buffer at pH 4.0 for the cathode and anode solutions, respectively. This system requires low voltages but compares well with isoelectric focusing using strong acid and strong base electrode solutions. The advantages of this method are the less extreme pH's in the electrode solutions and lower resistance in the neutral region of the pH gradients.