The possible role of intracellular lipid in determining oxygen delivery to fish skeletal muscle

Abstract

Transcellular oxygen flux in skeletal muscle fibres was modelled mathematically. In eels at the same environmental temperature (15°C), changes in muscle structure associated with increased levels of activity elevated mean fibre P O 2 by 30% to 5.2 kPa, despite greater fibre radius and V ̇ O 2 , due to more capillaries and intracellular lipid. The latter results in a 68% increase in oxygen permeability ( P O 2 ). While cold acclimation of striped bass (5 vs. 25°C) led to a modest (12%) fibre hypertrophy, V ̇ O 2 fell proportionately more (by 60%). A 50% increase in capillary supply again aids oxygen flux, while the presence of intracellular lipid effectively reverses the cold-induced decrease in P O 2 . The combined effect is to increase mean fibre P O 2 from 1.9 to 4.6 kPa and minimum P O 2 from 0.57 to 4.2 kPa, respectively. These data suggest little selection pressure exists to alter fibre composition in order to increase peripheral oxygen transport, while the magnitude of change in intracellular P O 2 is likely in excess of that required to maintain locomotory activity. Hence, there may be some other factor than P O 2 regulating structural reorganisation of muscle fine structure.