Diffusion of labelled substances through isolated rat diaphragm.

1. The rate of diffusion of [(14)C] sucrose through rat diaphragm muscle is dependent on the period of preliminary soaking of the muscle in Krebs solution at 36 degrees C. The ratio of the length of the diffusion path through the diaphragm to its geometrical thickness appears to fall from 4.39+/-0.38 (S.E. of the mean) to 2.23+/-0.18 after about 6 h of soaking.2. The area of the diaphragms available for diffusion is apparently constant at 0.3-0.4 of their total area.3. The measured thickness of the diaphragms increases by about 20% on soaking.4. Entry of [(131)I] iodide into the muscle fibres is detected as a fall in both steady state and non-steady state rates of diffusion through the diaphragm.5. Entry of [(14)C-methyl] decamethonium into the muscle cells is not evident from such diffusion studies in normal Krebs solution.