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Martin L Yarmush – One of the best experts on this subject based on the ideXlab platform.

  • oxygen Uptake Rates and liver specific functions of hepatocyte and 3t3 fibroblast co cultures
    Biotechnology and Bioengineering, 2007
    Co-Authors: Cheul H Cho, Jaesung Park, Deepak Nagrath, Arno W Tilles, Francois Berthiaume, Mehmet Toner, Martin L Yarmush
    Abstract:

    Bioartificial liver (BAL) devices have been developed to treat patients undergoing acute liver failure. One of the most important parameters to consider in designing these devices is the oxygen consumption rate of the seeded hepatocytes which are known to have oxygen consumption Rates 10 times higher than most other cell types. Hepatocytes in various culture configurations have been tested in BAL devices including those formats that involve co-culture of hepatocytes with other cell types. In this study, we investigated, for the first time, oxygen Uptake Rates (OUR)s of hepatocytes co-cultured with 3T3-J2 fibro- blasts at various hepatocyte to fibroblast seeding ratios. OURs were determined by measuring the rate of oxygen disappearance using a ruthenium-coated optical probe after closing and sealing the culture dish. Albumin and urea production Rates were measured to assess hepatocyte func- tion. Lower hepatocyte density co-cultures demonstrated significantly higher OURs (2 to 3.5-fold) and liver- specific functions (1.6-fold for albumin and 4.5-fold for urea pro- duction) on a per cell basis than those seeded at higher densities. Increases in OUR correlated well with increased liver-specific functions. OURs (Vm) were modeled by fitting Michaelis-Menten kinetics and the model predictions closely correlated with the experimental data. This study provides useful information for predicting BAL design parameters that will avoid oxygen limitations, as well as maximize metabolic functions. Biotechnol. Bioeng. 2007;97: 188-199.

  • oxygen Uptake Rates in cultured rat hepatocytes
    Biotechnology and Bioengineering, 1992
    Co-Authors: Avi Rotem, Martin L Yarmush, Menmet Toner, Ronald G Tompkins
    Abstract:

    One potential treatment of acute liver failure involves the use of an extracorporeal device composed of functional hepatocytes. A major issue in the design of such a large-scale device is providing the hepatocytes with a sufficient supply of oxygen and other nutrients. In this study, we have designed and characterized a simple perfusion system hepatocytes using this system. The OUR of hepatocytes was determined during the first day after seeding on a single collagen gel and during the long-term stable culture after the addition of a top layer of collagen. The OUR increased to 20.7 +/- 0.57 pmol/sec/microg DNA during the first 13 hours of culture on a single collagen gel, while during the next 11 hours, the OUR declined to 10.6 +/- 1.5 pmol/sec/microg DNA. In parallel with the increase in OUR during the first 10 hours, we observed significant cell spreading, suggesting that the oxygen supply to the cells may be critical for the spreading and adaptation of the anchorage-dependent hepatocytes following isolation. Addition of a top layer of collagen to hepatocyte cultures for 24 hours of culture on a single collagen layer resulted in a stable OUR for 15 days. These results indicate that OUR of hepatocytes in culture may vary depending on the phase of culture (i.e., early vs. late) and on the extracellular environment.

Paul J Harrison – One of the best experts on this subject based on the ideXlab platform.

  • Uptake of nitrate ammonium and urea by nitrogen starved cultures of micromonas pusilla prasinophyceae transient responses1
    Journal of Phycology, 1991
    Co-Authors: William P Corhlan, Paul J Harrison
    Abstract:

    Nitrogen Uptake Rates were measured as a function of time following saturating additions (15 μMg-at N·−1) of 15N-labelid ammonium, urea, and nitrate to N-starved cultures of the picoflagellate Micromonas pusilla Butcher. Uptake Rates were estimated from both the accumulation of 15N into the cells and the disappearance of nitrogen from the medium. Transient elevated (surge) Uptake Rates of NH4+ and urea were observed after enrichment. During the first 5 min the initial urea and NH4+ Uptake Rates were 2- and 4-fold greater than the maximum growth rate (μMmax)observed prior to No3− depletion in the cultures. The elevated urea Uptake Rates declined quickly to a relatively constant value, whereas the initial Rates of NH4+ Uptake declined rapidly but were followed by a subsequent increase prior to remaining roughly constant. Nitrate was not taken up as readily by N-starved M. pusilla as the reduced N forms. Although NO3+ Uptake commenced immediately after enrichment (i.e. no lag period) the N-Specific rate over the next 6 h averaged half the μMmax observed during NO3− replete conditions.

  • Uptake OF NITRATE, AMMONIUM, AND UREA BY NITROGEN‐STARVED CULTURES OF MICROMONAS PUSILLA (PRASINOPHYCEAE): TRANSIENT RESPONSES1
    Journal of Phycology, 1991
    Co-Authors: William P Corhlan, Paul J Harrison
    Abstract:

    Nitrogen Uptake Rates were measured as a function of time following saturating additions (15 μMg-at N·−1) of 15N-labelid ammonium, urea, and nitrate to N-starved cultures of the picoflagellate Micromonas pusilla Butcher. Uptake Rates were estimated from both the accumulation of 15N into the cells and the disappearance of nitrogen from the medium. Transient elevated (surge) Uptake Rates of NH4+ and urea were observed after enrichment. During the first 5 min the initial urea and NH4+ Uptake Rates were 2- and 4-fold greater than the maximum growth rate (μMmax)observed prior to No3− depletion in the cultures. The elevated urea Uptake Rates declined quickly to a relatively constant value, whereas the initial Rates of NH4+ Uptake declined rapidly but were followed by a subsequent increase prior to remaining roughly constant. Nitrate was not taken up as readily by N-starved M. pusilla as the reduced N forms. Although NO3+ Uptake commenced immediately after enrichment (i.e. no lag period) the N-Specific rate over the next 6 h averaged half the μMmax observed during NO3− replete conditions.

O. L. J. Van Asselen – One of the best experts on this subject based on the ideXlab platform.

William P Corhlan – One of the best experts on this subject based on the ideXlab platform.

  • Uptake of nitrate ammonium and urea by nitrogen starved cultures of micromonas pusilla prasinophyceae transient responses1
    Journal of Phycology, 1991
    Co-Authors: William P Corhlan, Paul J Harrison
    Abstract:

    Nitrogen Uptake Rates were measured as a function of time following saturating additions (15 μMg-at N·−1) of 15N-labelid ammonium, urea, and nitrate to N-starved cultures of the picoflagellate Micromonas pusilla Butcher. Uptake Rates were estimated from both the accumulation of 15N into the cells and the disappearance of nitrogen from the medium. Transient elevated (surge) Uptake Rates of NH4+ and urea were observed after enrichment. During the first 5 min the initial urea and NH4+ Uptake Rates were 2- and 4-fold greater than the maximum growth rate (μMmax)observed prior to No3− depletion in the cultures. The elevated urea Uptake Rates declined quickly to a relatively constant value, whereas the initial Rates of NH4+ Uptake declined rapidly but were followed by a subsequent increase prior to remaining roughly constant. Nitrate was not taken up as readily by N-starved M. pusilla as the reduced N forms. Although NO3+ Uptake commenced immediately after enrichment (i.e. no lag period) the N-Specific rate over the next 6 h averaged half the μMmax observed during NO3− replete conditions.

  • Uptake OF NITRATE, AMMONIUM, AND UREA BY NITROGEN‐STARVED CULTURES OF MICROMONAS PUSILLA (PRASINOPHYCEAE): TRANSIENT RESPONSES1
    Journal of Phycology, 1991
    Co-Authors: William P Corhlan, Paul J Harrison
    Abstract:

    Nitrogen Uptake Rates were measured as a function of time following saturating additions (15 μMg-at N·−1) of 15N-labelid ammonium, urea, and nitrate to N-starved cultures of the picoflagellate Micromonas pusilla Butcher. Uptake Rates were estimated from both the accumulation of 15N into the cells and the disappearance of nitrogen from the medium. Transient elevated (surge) Uptake Rates of NH4+ and urea were observed after enrichment. During the first 5 min the initial urea and NH4+ Uptake Rates were 2- and 4-fold greater than the maximum growth rate (μMmax)observed prior to No3− depletion in the cultures. The elevated urea Uptake Rates declined quickly to a relatively constant value, whereas the initial Rates of NH4+ Uptake declined rapidly but were followed by a subsequent increase prior to remaining roughly constant. Nitrate was not taken up as readily by N-starved M. pusilla as the reduced N forms. Although NO3+ Uptake commenced immediately after enrichment (i.e. no lag period) the N-Specific rate over the next 6 h averaged half the μMmax observed during NO3− replete conditions.

József Hlavay – One of the best experts on this subject based on the ideXlab platform.

  • Theoretical approach to non-constant Uptake Rates for tube-type diffusive samplers.
    Talanta, 2001
    Co-Authors: Balázs Tolnai, András Gelencsér, József Hlavay
    Abstract:

    Abstract A simple theoretical model was developed for evaluating the validity of the simplified Uptake model of diffusive sampling. In the model based on the plate theory diffusion to the adsorbent surface, phase equilibrium of the adsorbate and mass transport in the adsorbent bed were considered. It was found that in the early stage of sampling, the rate of sampling is close to its theoretical value. As sampling progresses, the concentration increases and the mass transfer front gradually moves into the adsorbent layer. Above a certain threshold limit, the mass Uptake becomes a steady state process in which the diffusion in the air gap and the mass transport in the adsorbent bed are balanced. As Uptake is a cumulative process, sampling should continue long enough to render the effects of these initial changes negligible. That is why constant Uptake Rates can still be obtained above a critical exposure dose. This critical exposure dose should be exceeded both in the determination of Uptake Rates and outdoor measurements, to obtain consistent and reliable analytical data. Evaluation of the time and concentration dependence of Uptake rate in laboratory experiments and the time dependence of Uptake rate in filed test was performed to justify the model results. Since the determination of Uptake Rates always takes places in the laboratory, where the exposure time is much shorter and the concentration is much higher than in the environment, the Uptake Rates are thus overestimated by 10–30%. Therefore, the Uptake Rates should be determined in the field under ambient conditions by means of an independent reference method.