# The composition of the interstitial fluid in the retina of the honeybee drone: implications for the supply of substrates of energy metabolism from blood to neurons

Cardinaud, B., Coles, J. A., Perrottet, P., Spencer, A. J., Osborne, M. P. and Tsacopoulos, M. (1994) The composition of the interstitial fluid in the retina of the honeybee drone: implications for the supply of substrates of energy metabolism from blood to neurons. Proceedings of the Royal Society of London Series B: Biological Sciences, 257(1348), pp. 49-58. (doi:10.1098/rspb.1994.0093)

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Publisher's URL: http://dx.doi.org/10.1098/rspb.1994.0093

## Abstract

Ion-selective microelectrodes were used to measure extracellular free ion concentrations in the retina of the drone honeybee, Apis mellifera male. Mean values were (in millimoles per litre): Na$^{+}$, 196; K$^{+}$, 10.2; Ca$^{2+}$, 2.0; pH 6.9. The elemental composition of fluid that rose into a micropipette inserted in the retina was obtained by electron microprobe X-ray analysis: from the concentrations of Na and K it was estimated that this fluid was 91% interstitial fluid. Amino acids and carbohydrates were analysed by chromatography. Four amino acids had concentrations > 20 mM: proline (109 mM), glutamine (38 mM), alanine (31 mM) and $\beta$-alanine (24 mM). These concentrations were higher than in the haemolymph. Other amino acids had concentrations of less than 3 mM. The identified carbohydrates were trehalose, glucose, pyruvate and fructose. All of these were less concentrated than in the haemolymph. These results: (i) show that the ion concentrations of previously used Ringer solutions were reasonably correct; (ii) demonstrate properties of the blood-retina barrier; (iii) suggest that the extracellular concentration of alanine is ample for it to serve as a major substrate of neuronal energy metabolism in this tissue.

Item Type: Articles Published Yes Coles, Dr Jonathan Cardinaud, B., Coles, J. A., Perrottet, P., Spencer, A. J., Osborne, M. P., and Tsacopoulos, M. College of Medical Veterinary and Life Sciences > Institute of Infection Immunity and Inflammation Proceedings of the Royal Society of London Series B: Biological Sciences The Royal Society 0962-8452 1471-2954

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