The nucleoside transporter family
| NT Process | Na+Dependence | Na+:Nuc Stoichiometry | Sensitivity To NBMPR | Substrate Specificity | Tissue Specificity |
|---|---|---|---|---|---|
| Equilibrative transporters | |||||
| es | — | + | Pur and Pyr Nuc | Widely expressed in mammalian cells | |
| ei | — | — | Pur and Pyr Nuc | Widely expressed in mammalian cells | |
| Concentrative Transporters | |||||
| cif (N1) | + | 1:1 | — | Pur Nuc, Urd | Mouse splenocytes, rat enterocytes, macrophages, liver, leukemic cells |
| cit (N2) | + | 1:1 | — | Pyr Nuc, Ado | Mouse enterocytes, rat/rabbit kidney |
| cit(N4) | + | 1:1 | — | Pyr Nuc, Ado, Guo | Human brush border kidney cells |
| cib (N3) | + | 2:1 | — | Pur and Pyr Nuc | Human colorectal, leukemic cells, CP, microglia |
| cs (N5) | + | N.D. | + | Ado analogs | Human leukemic cells |
| csg(N6) | + | 1:1 | + | Guo | Acute promyelocytic leukemic cells |
—, negative; +, positive; N.D., not determined; Pur, purine; Pyr, pyrimidine; Nuc, nucleosides; Urd, uridine; Ado, adenosine; Guo, guanosine. NT terminology: es, equilibrative, sensitive to nitrobenzylmercaptopurine riboside (NBMPR) inhibition; ei, equilibrative, insensitive to NBMPR; cif or N1, concentrative, NBMPR insensitive, accepts formycin B as a permeant;cit or N2, concentrative, NBMPR insensitive, common permeant, thymidine; cib or N3/N4, concentrative, NBMPR insensitive, broad specificity; cs or N5, concentrative, NBMPR sensitive; csg or N6, concentrative, NBMPR sensitive, accepts guanosine as a permeant. The corresponding cloned NT proteins both in humans and rats are: es = ENT1,ei = ENT2, cif (N1) = CNT2/SPNT,cit (N2) = CNT1. Adapted from Wang et al., 1997a; Cass et al., 1998.