Competition between catecholamines and glucose for binding sites on proteins of erythrocytes
Michael Lepschy, Erich Moestl & Rupert Palme
Glucose is slowly linked to haemoglobin in a non-enzymatic reaction and the determination of a glycated protein (HbA1c) is used for long term monitoring blood glucose concentrations. Radiometabolism studies in sheep showed that a haemoglobin-adduct formation also takes place with epinephrine or norepinephrine.
The aim of our study was to elucidate if there is a competition between catecholamines and glucose for binding sites on proteins of the erythrocytes.
Heparinised canine blood was obtained and centrifuged at 1500 g and the cells were washed three times with isotonic NaCl-solution. Afterwards, 5 portions of erythrocytes (0.7 ml each) were re-suspended in 7 ml TCM Eagle and incubated with epinephrine and norepinephrine (1 and 10 ng/ml) for 3 days at 38.6 °C. One portion served as control.
Afterwards the erythrocyte portions were split into sub-samples of 0.2 ml each. One half was incubated with 3H-norepinephrine for 1 h (unhaemolysed), the second half with 14C-glucose for 10 days after haemolysis by freezing. To determine the uptake of 3H-norepinephrine, samples were centrifuged and the radioactivity of the supernatant was measured. In total 410±7 Bq of the added 574±16 Bq were measured in the control samples, whereas all groups preincubated with non-radioactive catecholamines showed significantly (P<0.05) higher radioactivity. To determine the binding of 14C-glucose, proteins were precipitated. After centrifugation, 567±24 Bq of the added 1916±80 Bq were measured in the supernatant of the control samples. As in the experiment using 3H-norepinephrine, significant (P<0.05) higher values were measured in the supernatant of the preincubated erythrocytes, indicating a lower binding of 14C-glucose to the proteins.
Therefore we conclude that catecholamines are blocking binding sites on proteins of erythrocytes for additional adduct formation with 3H-norepinephrine or 14C-glucose.