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Journal of Experimental Biology, Vol 203, Issue 16 2479-2484, Copyright © 2000 by Company of Biologists

JOURNAL ARTICLES

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

GS Timmins, EJ Bechara and HM Swartz
EPR Centre for the Study of Viable Systems, Department of Radiology, Dartmouth Medical School, Hanover, NH 03755, USA. timminsgs@cardiff.ac.uk

We describe the development and use of a direct kinetic technique to determine 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 time 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 helium 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 pathlengths of diffusion in the gaseous and aqueous phases of 4.80x10(-)(3)+/-0.53x10(-)(3) and 8. 89x10(-)(5)+/-0.61x10(-)(5 )m, respectively. In addition, the pathlength of gas-phase diffusion was used to derive a parameter relating to the tortuosity of the tracheal system. These values, together with those obtained upon bioluminescent oxygen consumption, have been used to model oxygen supply to the photocyte. From these studies, it would also appear that the modulation of tracheolar fluid levels might be a significant mechanism of control of tissue oxygen levels in at least some insects.
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G. S. TIMMINS, F. J. ROBB, C. M. WILMOT, S. K. JACKSON, and H. M. SWARTZ
FIREFLY FLASHING IS CONTROLLED BY GATING OXYGEN TO LIGHT-EMITTING CELLS
J. Exp. Biol., March 10, 2002; 204(16): 2795 - 2801.
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