UPTAKE AND METABOLISM OF GLUCOSE, ALANINE AND LACTATE BY RED-BLOOD-CELLS OF THE AMERICAN EEL ANGUILLA-ROSTRATA

The uptake and metabolism of glucose, alanine and lactate were assesse d in red blood cells (RBCs) of the American eel Anguilla rosh ata. L-L actate was metabolized at the highest rates as assessed by O-2 consump tion and CO2 production, followed by glucose and alanine (rates were a pproximately half of those observed for lactate), A saturable (K-m 10. 36+/-0.60 mmol l(-1), J(max) 27.42+/-2.16 mu mol 3-OMG l(-1) cell wate r min(-1)) sodium-independent but cytochalasin-B- sensitive carrier fo r D-glucose was observed, which was stereospecific and inhibited by ot her hexoses, These characteristics are in agreement with those reporte d for the GLUT-1 glucose carrier of human and Japanese eel erythrocyte s. These cells also contained a saturable carrier for L-lactate in the concentration range 0-10 mmol l(-1) (K-m 6.74+/-0.36 mmol l(-1), J(ma x) 2.29+/-0.09 mmol lactate l(-1) cell water min(-1)) whereas, at high er concentrations (10-40 mmol l(-1)), transport occurred by simple dif fusion. The carrier was stereospecific, sodium-independent, fully inhi bited by alpha-cyano-4-hydroxycinnamate, DIDS and pyruvate, but less s ensitive to SITS, IBCLA and pCMBS, We suggest that this carrier is sim ilar to the H+/monocarboxylate carrier found in mammalian RBCs, Despit e the fact that L-alanine transport did not saturate, transport was st ereospecific because it was inhibited by D-alanine, These experiments do not, therefore, exclude the existence of an alanine carrier in the eel RBC, The rates of substrate uptake exceeded the ability of the RBC to metabolize the substrate (using 1 mmol l(-1) extracellular concent ration), with uptake rate/metabolic rate ratios being 2 for alanine, 5 for glucose and 151 for lactate, These experiments indicate that upta ke does not limit the ability of the American eel RBC to utilize gluco se, alanine or lactate, but that the mechanism(s) of substrate uptake is species-specific.