Diffusion of myoglobin in skeletal muscle cells - dependence on fibre type, contraction and temperature

We measured the diffusion coefficient of myoglobin (DMb) inside mammalian skeletal muscle cells with a microinjection technique. A small bolus of horse Mb was injected into a single muscle fibre and the subsequent time-dependent changes of the Mb profiles along the fibre axis were measured with a microscope-photometer. For fibres of the rat soleus muscle at 22° C, a DMb of 1.3·10−7 cm2/s was found, confirming a result obtained previously by us for rat diaphragm muscle with a photo-oxidation technique. In the extensor digitorum longus muscle of the rat, a higher value of 1.9 · 10−7 cm2/s was measured. Auxotonic muscle contractions did not change the apparent DMb. For the temperature range between 22 ° C and 37 ° C, a temperature coefficient, Q10, of 1.5 was calculated. The implication of this result for the role of Mb in the facilitation of oxygen transport was examined. Model calculations show that with this relatively low DMb value, the intracellular oxygen supply can be improved only slightly.