Inosine uptake by cultured fibroblasts from normal and purine nucleoside phosphorylase-deficient humans.

Purine nucleoside phosphorylase-deficient cultured human fibroblasts accumulate inosine from the medium at 60% of the rate in wild type cells when the extracellular inosine concentration is 10 micronM and 30% of the normal rate when inosine is present at 100 micronM. When 10 micronM inosine is present, uridine but not hypoxanthine inhibits the accumulation of inosine. There exist two transport systems for inosine. One is shared with pyrimidine ribonucleosides and is the predominant one at 10 micronM inosine; the other is purine nucleoside phosphorylase-dependent and prevails at 100 micronM inosine.