Na+ reabsorption in cultured rat epididymal epithelium via the Na+/nucleoside cotransporter

Biol Reprod. 2001 Mar;64(3):764-9. doi: 10.1095/biolreprod64.3.764.

Abstract

The effect of nucleoside on Na+ reabsorption via Na+/nucleoside cotransporter in cultured rat epididymal epithelia was studied by short-circuit current (Isc) technique. Guanosine added apically stimulated Isc in a dose-dependent manner, with a median effective concentration (EC50) of 7 +/- 2 microM (mean +/- SEM). Removal of Na+ from the apical bathing solution or pretreatment with a nonspecific Na+/nucleoside cotransporter inhibitor, phloridzin, completely blocked the Isc response to guanosine. Moreover, the guanosine response was abolished by pretreatment of the tissue with ouabain, a Na+/K+-ATPase inhibitor, suggesting the involvement of Na+/nucleoside cotransporter on the apical side and Na+/K+-ATPase on the basolateral side in Na+ reabsorption. In contrast, the Isc response to guanosine was not affected after desensitization of purinoceptors by ATP. Addition of the Na+/K+/2Cl- symport inhibitor bumetanide to the basolateral side or the nonspecific Cl- channel blocker diphenylamine-2-carboxylate to the apical side showed no effect on the Isc response to guanosine, excluding stimulation of Cl- secretion by guanosine as the cause of the guanosine-induced Isc. The Isc response to purine nucleoside (guanosine and inosine) was much higher than that to pyrimidine nucleoside (thymidine and cytidine). Consistent with substrate specificity, results of reverse transcription-polymerase chain reaction revealed mRNA for concentrative nucleoside transporter (CNT2), which is a purine nucleoside-selective Na+/nucleoside cotransporter in the epididymis, but not for CNT1. It is suggested that the Na+/nucleoside cotransporter (i.e., CNT2) may be one of the elements involved in Na+ and fluid reabsorption in the epididymis, thereby providing an optimal microenvironment for the maturation and storage of spermatozoa.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Absorption
  • Adenosine Triphosphate / pharmacology
  • Animals
  • Bumetanide / pharmacology
  • Calcium Channel Blockers / pharmacology
  • Carrier Proteins / biosynthesis
  • Carrier Proteins / genetics
  • Carrier Proteins / metabolism*
  • Chloride Channels / antagonists & inhibitors
  • Chloride Channels / physiology
  • DNA / chemistry
  • DNA / genetics
  • DNA / metabolism
  • Epididymis / metabolism*
  • Epithelial Cells / metabolism
  • Gene Expression
  • Guanosine / pharmacology*
  • Male
  • Membrane Transport Proteins*
  • Patch-Clamp Techniques
  • Phlorhizin / pharmacology
  • RNA, Messenger / genetics
  • RNA, Messenger / metabolism
  • Rats
  • Rats, Sprague-Dawley
  • Reverse Transcriptase Polymerase Chain Reaction
  • Sodium / metabolism*
  • Sodium-Potassium-Exchanging ATPase / antagonists & inhibitors
  • Sodium-Potassium-Exchanging ATPase / metabolism
  • Substrate Specificity
  • ortho-Aminobenzoates / pharmacology

Substances

  • Calcium Channel Blockers
  • Carrier Proteins
  • Chloride Channels
  • Membrane Transport Proteins
  • RNA, Messenger
  • cif nucleoside transporter
  • ortho-Aminobenzoates
  • Bumetanide
  • Guanosine
  • Adenosine Triphosphate
  • DNA
  • fenamic acid
  • Sodium
  • Phlorhizin
  • Sodium-Potassium-Exchanging ATPase