Sodium-dependent nucleoside transport in rabbit intestinal epithelium.
Cellular uptake of formycin B, a poorly metabolized analog of inosine, by the isolated epithelium of rabbit jejunum is three times higher in the presence of Na+ than without this cation. The Na(+)-dependent nucleoside transport system is located in the apical membrane of the enterocytes and is capable of uphill transport, as shown for formycin B and adenosine with brush border membrane vesicles. According to present and earlier evidence, nucleoside transport across the basolateral membrane appears to have the properties of facilitated diffusion. Na(+)-dependent formycin B transport activity in intestinal epithelium decreases from jejunum to ileum and is absent in descending colon. As with Na(+)-coupled cotransport systems for other organic solutes, apical entry of formycin B is driven by the electrochemical Na+ gradient into the cell. In contrast to the facilitated diffusion system for nucleosides, Na(+)-dependent formycin B transport is not inhibited by nitrobenzylthioinosine, but both carrier systems are sensitive to inhibitors of D-glucose transport. Natural purine nucleosides and uridine are strong inhibitors of Na(+)-dependent formycin B transport. Transepithelial flux measurements substantiated that the Na(+)-dependent transport mechanism for formycin B functions as an absorptive system.
Roden
M
M
Pharmakologisches Institut, Universität Wien, Vienna, Austria.
Paterson
A R
AR
Turnheim
K
K
D000818:Animals; D001693:Biological Transport, Active / Q000502:physiology; D002352:Carrier Proteins / Q000378:metabolism; D004848:Epithelium / Q000378:metabolism; D005573:Formycins / Q000493:pharmacokinetics*; D007408:Intestinal Absorption / Q000502:physiology; D007413:Intestinal Mucosa / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism; D033703:Nucleoside Transport Proteins; D009705:Nucleosides / Q000378:metabolism*; D011817:Rabbits; D012964:Sodium / Q000502:physiology*
D002352:Carrier Proteins; D005573:Formycins; D008565:Membrane Proteins; D033703:Nucleoside Transport Proteins; D009705:Nucleosides; C034561:formycin B; D012964:Sodium