Characterization of nucleoside transport systems in cultured rat epididymal epithelium

The nucleoside transport systems in cultured epididymal epithelium were cha racterized and found to be similar between the proximal (caput and corpus) and distal (cauda) regions of the epididymis. Functional studies revealed t hat 70% of the total nucleoside uptake was Na+ dependent, while 30% was Na independent. The Na+-independent nucleoside transport was mediated by both the equilibrative nitrobenzylthioinosine (NBMPR)-sensitive system (40%) an d the NBMPR-insensitive system (60%), which was supported by a biphasic dos e response to NBMPR inhibition. The Na+-dependent [H-3] uridine uptake was selectively inhibited 80% by purine nucleosides, indicating that the purine nucleoside-selective N1 system is predominant. Since Na+-dependent [H-3] g uanosine uptake was inhibited by thymidine by 20% and Na+-dependent [H-3] t hymidine uptake was broadly inhibited by purine and pyrimidine nucleosides, this suggested the presence of the broadly selective N3 system accounting for 20% of Na+-dependent nucleoside uptake. Results of RT-PCR confirmed the presence of mRNA for equilibrative nucleoside transporter (ENT) 1, ENT2, a nd concentrative nucleoside transporter (CNT) 2 and the absence of CNT1. It is suggested that the nucleoside transporters in epididymis may be importa nt for sperm maturation by regulating the extracellular concentration of ad enosine in epididymal plasma.