Biophysical Journal 54: 655-667 (1988)
© 1988 the Biophysical Society

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Kinetics of Oxygen Consumption after a Flash of Light in the Lateral Ocellus of the Barnacle

ABSTRACT

Until recently, polarographic methods for measuring the time course of transient changes in the rate of oxygen consumption (QO₂) have been applied only to tissue preparations containing thousands of cells. Here, we describe QO₂ measurements on the lateral ocellus of the barnacle (Balanus eburneus) which contains only three photoreceptor cells. The decrement of partial pressure of oxygen (PO₂) elicited by an 80 ms flash of light was measured near the cells with a microelectrode and the QO₂ was calculated from the PO₂ using a model of diffusion with spherical symmetry. As shown by mathematical simulation, the exact shape of the preparation is not crucial for our measurements of the time course of the QO₂. For a given QO₂, the model describes correctly the attenuation of the PO₂ measured at increased distances from the preparation. To know more about the mechanisms controlling the QO₂, we compared it with the electrical response of the photoreceptor cells: both responses have a similar spectral dependence, but only the QO₂ was abolished by a 10-min exposure to 50 µM dinitrophenol or to 3 mM amytal. We conclude that the QO₂ reflects an increase in mitochondrial respiration and that it is initiated by the phototransformation of rhodopsin, as was already found in the honeybee drone retina (Dimitracos and Tsacopoulos, 1985; Jones and Tsacopoulos, 1987).