School of Engineering, University of Waikato, Hamilton 3240, New Zealand.
Anaesthesia Department, Waikato District Health Board, Hamilton 3204, New Zealand.
Int J Mol Sci. 2023 Mar 29;24(7):6450. doi: 10.3390/ijms24076450.
To investigate the impact of experimental interventions on living biological tissue, ex vivo rodent brain slices are often used as a more controllable alternative to a live animal model. However, for meaningful results, the biological sample must be known to be healthy and viable. One of the gold-standard approaches to identifying tissue viability status is to measure the rate of tissue oxygen consumption under specific controlled conditions. Here, we work with thin (400 μm) slices of mouse cortical brain tissue which are sustained by a steady flow of oxygenated artificial cerebralspinal fluid (aCSF) at room temperature. To quantify tissue oxygen consumption (), we measure oxygen partial pressure (pO2) as a function of probe depth. The curvature of the obtained parabolic (or parabola-like) pO2 profiles can be used to extract , providing one knows the Krogh coefficient Kt, for the tissue. The oxygen trends are well described by a Fick's law diffusion-consumption model developed by Ivanova and Simeonov, and expressed in terms of ratio (Q/K), being the rate of oxygen consumption in tissue divided by the Krogh coefficient (oxygen diffusivity × oxygen solubility) for tissue. If the fluid immediately adjacent to the tissue can be assumed to be stationary (i.e., nonflowing), one may invoke conservation of oxygen flux K·(∂P/∂x) across the interface to deduce (Kt/Kf), the ratio of Krogh coefficients for tissue and fluid. Using published interpolation formulas for the effect of salt content and temperature on oxygen diffusivity and solubility for pure water, we estimate Kf, the Krogh coefficient for aCSF, and hence deduce the Kt coefficient for tissue. We distinguish experimental uncertainty from natural biological variability by using pairs of repeated profiles at the same tissue location. We report a dimensionless Krogh ratio (Kt/Kf)=0.562±0.088 (mean ± SD), corresponding to a Krogh coefficient Kt=(1.29±0.21)×10-14 mol/(m·s·Pa) for mouse cortical tissue at room temperature, but acknowledge the experimental limitation of being unable to verify that the fluid boundary layer is truly stationary. We compare our results with those reported in the literature, and comment on the challenges and ambiguities caused by the extensive use of 'biologically convenient' non-SI units for tissue Krogh coefficient.
为了研究实验干预对活体生物组织的影响，通常使用离体啮齿动物脑片作为比活体动物模型更可控的替代方法。然而，为了获得有意义的结果，生物样本必须被证明是健康且有活力的。鉴定组织活力状态的一种金标准方法是在特定的控制条件下测量组织的耗氧量。在这里，我们使用 400μm 厚的小鼠皮质脑片作为研究对象，这些脑片在室温下持续受到含氧人工脑脊液(aCSF)的稳定流动的支持。为了量化组织耗氧量()，我们测量氧分压(pO2)作为探针深度的函数。所获得的抛物线(或类似抛物线)pO2 曲线的曲率可以用来提取，前提是已知组织的克洛夫系数(Kt)。氧趋势很好地符合由 Ivanova 和 Simeonov 开发的菲克扩散消耗模型，并以氧消耗率与克洛夫系数(Q/K)之比表示，其中组织中的氧消耗率除以组织的克洛夫系数(氧扩散率×氧溶解度)。如果可以假设组织附近的流体是静止的(即非流动的)，则可以根据氧通量 K·(∂P/∂x)在界面上的守恒来推断(Kt/Kf)，即组织和流体的克洛夫系数之比。使用已发表的关于盐含量和温度对纯水中氧扩散率和溶解度影响的插值公式，我们估计 aCSF 的克洛夫系数 Kf，并由此推断组织的 Kt 系数。我们通过在同一组织位置使用重复的曲线对来区分实验不确定性和自然生物学变异性。我们报告无量纲克洛夫系数(Kt/Kf)=0.562±0.088(平均值±标准差)，对应于室温下小鼠皮质组织的克洛夫系数 Kt=(1.29±0.21)×10-14 mol/(m·s·Pa)，但承认无法验证流体边界层是否真正静止的实验局限性。我们将我们的结果与文献中的结果进行比较，并讨论了由于广泛使用“生物方便”的非 SI 单位来表示组织克洛夫系数而导致的挑战和歧义。
