Nucleoside transport in sheep erythrocytes: genetically controlled transport variation and its influence on erythrocyte ATP concentrations.

Abstract

SUMMARY1. The permeability of sheep erythrocytes to purine and pyrimidine nucleosides was investigated. Erythrocytes from most sheep (nucleoside-impermeable) were almost completely impermeable to 5 mM inosine whereas cells from approximately 5 % of the animals studied (nucleoside-permeable) showed a rapid inosine uptake.Cells from both types of animal were permeable to 5 mm adenosine, although transport was slower in nucleoside-impermeable erythrocytes.2. Two distinct nucleoside transport routes were present in nucleoside-permeable erythrocytes; a high affinity (apparent Km -0-2 mM) facilitated diffusion system which transported both purine and pyrimidine nucleosides, and a non-saturable uptake route selective for adenosine. The high affinity system was the major route of adenosine transport at physiological concentrations. 3. Transport by the high affinity system was completely inhibited by micromolar concentrations of dipyridamole and nitrobenzylthioinosine. Dipyridamole had no effect on the non-saturable component of adenosine uptake.4. The transport differences between nucleoside-permeable and impermeable erythrocytes were due to the absence of the high affinity system from nucleosideimpermeable cells.5. Nucleoside-permeable cells had a higher intracellular ATP concentration than nucleoside-impermeable erythrocytes, suggesting that the high affinity transport system participates in the energy metabolism of the cell.

Nucleoside and glucose transport in erythrocytes from new‐born lambs

“…In both cases uptake was consistent with simple Michaelis-Menten kinetics giving apparent Km values of 0 35 and 0-4 mM for the nucleoside-permeable and impermeable lambs respectively. For comparison, the apparent Km value for inosine uptake by nucleoside-permeable cells from adult sheep has previously been estimated to be 0-26 mm (Young, 1978). Inosine uptake by nucleoside-impermeable erythrocytes from adult sheep is slow and nonsaturable.…”

“…Both dipyridamole and nitrobenzylthioinosine were extremely effective inhibitors of inosine uptake (1 mM) by fetal cells from both types of animal (> 80% inhibition at 1 /SM). Uridine and adenosine (5 mM) were also effective inhibitors of inosine uptake (1 mM) by fetal cells from nucleoside-permeable and impermeable animals (65% and 78% inhibition respectively with uridine and cases was similar to that given by adult permeable erythrocytes (see Young, 1978).…”

“…The washing procedure did not result in loss of radioactivity from the cells, and both the washing and dibutyl phthalate methods gave equivalent uptake rates (Young, 1978).…”

“…This applies to glucose transport in a number of species including the sheep and pig (Widdas, 1955;Augustin, Rohden & Hacker, 1967; Lee, Auvil, Grey & Smith, 1976; Zeidler, Lee & Kim, 1976), sodium and potassium transport in the dog (Lee & Miles, 1972;Miles & Lee, 1972), cattle (Israel, MacDonald, Bernstein & Rosenmann, 1972) and sheep (Ellory & Tucker, 1969;Tucker & Ellory, 1970) and calcium activated potassium transport in the sheep (Brown, Ellory, Young & Lew, 1978). Sheep are of particular N. A. MOONEY AND J. D. YOUNG interest because as adults they show genetic polymorphism in the transport of sodium and potassium (Ellory, 1977), amino acids (Young, Ellory & Tucker, 1976) and nucleosides (Young, 1978). In the case of nucleoside transport some sheep (nucleoside-permeable phenotype) have cells which possess a high affinity transport system for both purine and pyrimidine nucleosides.…”

“…The permeability difference between the two types of animal is under the control of two allelomorphic genes (NuI and Nui) with the gene for nucleoside impermeability (NuI) behaving as if dominant to the gene for nucleoside permeability (Nui) (Jarvis & Young, 1978). Nucleoside-permeable erythrocytes have a higher ATP concentration than nucleoside-impermeable cells suggesting that the transport system participates in the energy metabolism of the erythrocyte (Young, 1978). This paper presents data on the nucleoside permeability of erythrocytes from newborn lambs of the two phenotypes.…”