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
B. Cardinaud et al., 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 - Royal Society. Biological Sciences, 257(1348), 1994, pp. 49-58
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;
Ca2+, 2.0; pH 6.9. The elemental composition of fluid that rose into
a micropipette inserted in the retina was obtained by electron micropr
obe X-ray analysis: from the concentrations of Na and K it was estimat
ed that this fluid was 91% interstitial fluid. Amino acids and carbohy
drates were analysed by chromatography. Four amino acids had concentra
tions > 20 mM: proline (109 mM), glutamine (38 mM) alanine (31 mM) and
beta-alanine (24 mM). These concentrations were higher than in the ha
emolymph. Other amino acids had concentrations of less than 3 mM. The
identified carbohydrates were trehalose, glucose, pyruvate and fructos
e. All of these were less concentrated than in the haemolymph. These r
esults: (ij 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 concentrat
ion of alanine is ample for it to serve as a major substrate of neuron
al energy metabolism in this tissue.