Direct determination of the kinetics of oxygen diffusion to the photocytesof a bioluminescent elaterid larva, measurement of gas- and aqueous-phase diffusional barriers and modelling of oxygen supply

We describe the development and use of a direct kinetic technique to determ ine the time taken for oxygen to diffuse from the external environment into the light-producing cells (photocytes) in the prothorax of bioluminescent larvae of Pyrearinus termitilluminans, This was achieved by measuring the t ime course of the pseudoflash induced through sequential anoxia followed by normoxia. We have also determined the separate times taken for this oxygen diffusion in gaseous and tissue (predominantly aqueous) phases by using he lium and nitrogen as the carrier gas. Of the total time taken for diffusion , that in the gas phase required 613+/-136 ms (mean +/- S.E.M., N=5) whilst that in the aqueous phase required 1313+/-187 ms. These values imply pathl engths of diffusion in the gaseous and aqueous phases of 4.80x10(-3)+/-0.53 x10(-3) and 8.89x10(-5)+/-0.61x10(-5) m, respectively. In addition, the pat hlength of gas-phase diffusion was used to derive a parameter relating to t he tortuosity of the tracheal system. These values, together with those obt ained upon bioluminescent oxygen consumption, have been used to model oxyge n supply to the photocyte, From these studies, it would also appear that th e modulation of tracheolar fluid levels might be a significant mechanism of control of tissue oxygen levels in at least some insects.