[Dynamics and kinetics of 14C-nicotinic acid uptake by leukocytes and erythrocytes as an index of vitamin PP transport regulation].

Abstract

Isolated leukocytes with the presence of 14C-nicotinate in physiological concentrations (1 mg%) uptake it intensely from the dilute plasm for 6h. Dynamics of the uptake is characterized by two maxima (30-50 min and 3-5 h) which might reflect metabolic transformation of vitamin PP in leukocytes. Isolated erythrocytes and blood plasma proteins under these conditions accumulate the labelled vitamin in the largest amounts for first minutes of incubation without subsequent changes, accumulation of the labelled nicotinate by erythrocytes is 20 times as low as that by leukocytes. Kinetics of 14C-nicotinate uptake in increasing concentrations (from 4.0 up to 50.0 mM) by isolated leukocytes indicates to a system of this vitamin intake through the plasmatic membrane ensuring its intensive transport into cells with the present of 3.0-6.5 mM of nicotinic acid and a step inhibition of the label accumulation at higher concentrations which reflects decompensation of the vitamin-barrier function of the leukocytes plasma membranes with a rise in the nicotinate concentration in the medium from 6.5 to 16.3 mM the label accumulation is inhibited not only by leukocytes but also by erythrocytes. However the blood plasma proteins still bind 14C-nicotinate when it is present in the medium in linearly increasing high concentrations (16.0 = 50 mM).