Characterization of nucleoside transport systems in cultured rat epididymal epithelium

• Published in: American Journal of Physiology: Cell Physiology 2001-05, Vol.280 (5), p.C1076-C1082
• Main Authors: Leung, George P. H, Ward, Jeffrey L, Wong, Patrick Y. D, Tse, Chung-Ming
• Format: Article
• Language: English
• Subjects: Animals; Biological Transport - drug effects; Carrier Proteins - genetics; Carrier Proteins - metabolism; Cells, Cultured; Epididymis - cytology; Epididymis - physiology; Epithelial Cells - cytology; Epithelial Cells - physiology; Equilibrative Nucleoside Transporter 1; Equilibrative-Nucleoside Transporter 2; Guanosine - metabolism; Male; Membrane Proteins - genetics; Membrane Proteins - metabolism; Membrane Transport Proteins; Nucleosides - metabolism; Rats; Rats, Sprague-Dawley; Reverse Transcriptase Polymerase Chain Reaction; Sodium - physiology; Thioinosine - analogs & derivatives; Thioinosine - pharmacology; Thymidine - metabolism; Tritium; Uridine - metabolism
• ISSN: 0363-6143; 1522-1563
• DOI: 10.1152/ajpcell.2001.280.5.c1076

1  Division of Gastroenterology, Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205; and 2  Department of Physiology, The Chinese University of Hong Kong, Hong Kong, People's Republic of China The nucleoside transport systems in cultured epididymal epithelium were characterized and found to be similar between the proximal (caput and corpus) and distal (cauda) regions of the epididymis. Functional studies revealed that 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%) and the NBMPR-insensitive system (60%), which was supported by a biphasic dose response to NBMPR inhibition. The Na + -dependent [ 3 H]uridine uptake was selectively inhibited 80% by purine nucleosides, indicating that the purine nucleoside-selective N1 system is predominant. Since Na + -dependent [ 3 H]guanosine uptake was inhibited by thymidine by 20% and Na + -dependent [ 3 H]thymidine 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, and concentrative nucleoside transporter (CNT) 2 and the absence of CNT1. It is suggested that the nucleoside transporters in epididymis may be important for sperm maturation by regulating the extracellular concentration of adenosine in epididymal plasma. sperm maturation