Transport of hexoses, potassium and neutral amino acids into capillaries isolated from bovine retina.

Capillaries were isolated from bovine retina by homogenization and glass bead filtration in order to study their ability to transport certain solutes. Viability of the microvessels was demonstrated by their ability to maintain linear rates of substrate oxidation for more than two hours. He.uose uptake (measured using 3-o-methyl-D-glucose) could be inhibited b3 cytochalasin R, phloretin and phlorizin, but not, by 2,4-dinitrophenol or ouabain. D-l&CO%?, %deosy-n-glucose, D-mannose, n-galactose and D-XJdOSe inhibited 3-o-meth3rl-D-glucose uptake, while ~-glucose, D-ribose and n-fructose did not. When incubated at 37°C with 5 rn>l-u-glucose, the microvessels contained much more free u-glucose than D-glucose metabolites. Thus, transport was not rate limiting for metabolism. L-Glucose entered capillaries more slowly t.han other hexoses and served as a ma&er for simple diffllsion of suqers into the cells. ssRb+ was used as an indicator of I(+transport activity. Uptake of a@b+ was temperature sensit.ive and markedly inhibited by 1 mu ouabain, thus indicating the presence of an active K+ transport system. Na+-dependent amino acid transport was demonstrated using a-(methylamino)isobutyric acid as a model substrate. Capillary uptake of this neutral amino acid analogue was inhibited after abolishing the Xa+ gradient with ? mnl-ouabain. Uptake of the organic anionp-aminohippuric acid (PAH) was slightly greater f,han uptake of the estracellnlar marker sucrose. There was a small inhibition of PAH uptake by fluorescein and penicillin but not by probenicid. Our results indicate the presence of several transport processes in retinal capillary endothelial cells which may be important for the maintenance of homeostasis within the retina. liey tcorcls : glucose ; 3-o-methylglucose ; cytochalasin B; phloretin; phlorizin; glucose transport stereospecificity; rubidium; cr-(methylamino)-isobutyric acid; p-aminohippuric acid; endothelial cells; metabolism.