The contribution of adherent films of liquid on the cut surfaces of mouse brain slices to tissue water and "extracellular" marker space.

Abstract

1. Equations for surface film thicknesses and “surface” spaces are derived from a simple geometric model of a tissue slice. 2. In agreement with this model, the tissue water, inulin space, and sucrose space of slices of mouse cerebrum exposed briefly to the incubation medium or to the marker substance increase linearly with slice thinness (I/thickness). 3. The adherent film of medium on the cut surfaces of brain slices has an effective thickness of 0.0056 mm at 0°C, and 0.0085 mm at 37°C. 4. On cut surfaces of unicubated tissue, the effective film thickness measured with inulin is 0.0080 mm at 0°C, and 0.015 mm at 37°C because of superficial penetration into damaged tissue. After incubation for 60 min these thicknesses become 0.014 mm at 0°C, and 0.022 mm at 37°C. The effective film thickness measured with sucrose is even larger because of greater penetration. 5. The adherent film of medium on cut surfaces contributes appreciably to the fluid content of slices. At 0°C it adds 0.27 ml/g of dry tissue or 7% to the fluid content of a fresh unincubated 0.2-mm thick slice, and 0.14 ml/g of dry tissue or 3.5% to the fluid content of a 0.4-mm slice; at 37°C it adds 0.41 ml/g of dry tissue or 11%, and 0.21 ml/g of dry tissue or 5% respectively.