The Role of Na⁺−H⁺ Exchange in Fluid and Solute Transport in the Rat Efferent Ducts

Abstract

summaryIn vivo microperfusion techniques were used to investigate the role of Na¤-H¤ exchange in the efferent ducts of the rat. Individual efferent ducts were perfused with a Krebs-Ringer bicarbonate solution (KRB) containing 0, 1, 3, 5 or 7·5 mÒ amiloride. Concentrations of 1-5 mÒ amiloride inhibited fluid reabsorption from the efferent ducts in a linear dose-dependent manner with an apparent Km of 3 mÒ. Inhibition was maximal at 5 mÒ with reabsorption reduced by about 70%. The effects of amiloride were completely reversible and there was little effect of amiloride on luminal osmolality and concentrations of Na¤, Cl¦ or K¤.

Fluid Reabsorption by the Ductuli Efferentes Testis of the Rat Is Dependent on Both Sodium and Chlorine1

“…The findings are consistent with our previous work [10] showing the importance of the Na ϩ -H ϩ antiport, NHE3 [11], in fluid reabsorption by the ducts. The present studies also demonstrate that fluid reabsorption from the efferent ducts is dependent on both Na ϩ and Cl Ϫ transport, and that the transport of the ions is interdependent (i.e., the flux rates are parallel).…”

“…Anion Exchanger to Achieve Electroneutral Movement of Na ϩ and Cl Ϫ It is suggested that, as in the proximal kidney tubules [28], there is probably some form of apical anion antiporter operating in parallel with the Na ϩ -H ϩ antiporter [10,11] in order to achieve an electroneutral movement of Na ϩ and Cl Ϫ across the efferent duct epithelium. Such a linkage would explain why Cl Ϫ was fluxed at a greater rate than Na ϩ during reabsorption, and at a lower rate than Na ϩ during movement into the lumen, and why [Na ϩ ] in the collectate is greater than [Cl Ϫ ].…”

“…Reabsorption from both solutions was isosmolar for Na ϩ and Cl Ϫ , but K ϩ was reabsorbed at a greater rate than water from the nRTF [9]. Including amiloride in the KRB perfusate reduced reabsorption up to 70% in a dose-dependent manner [10], indicating that a significant proportion of the process is effected by an amiloridesensitive Na ϩ -H ϩ exchanger (NHE) that has been localized in the efferent duct epithelium [11].…”

Signal Transduction in the Ductuli Efferentes Testis of the Rat: Inhibition of Fluid Reabsorption by Cyclic Adenosine 3′, 5′-Monophosphate1

“…The proximal tubules have the same principal transporter for Na ϩ and fluid reabsorption, NHE3, and cAMP inhibits this Na ϩ /H ϩ antiporter [42][43][44][45], causing a reduction in Na ϩ and fluid reabsorption [26][27][28][29][30]. However, cAMP probably acts on more than NHE3 in the efferent ducts, as inhibition of NHE3 by amiloride can only reduce fluid reabsorption by 70% [5], whereas db-cAMP completely inhibits reabsorption at a concentration of 0.25 mM or more (Fig. 1).…”

“…Net fluid reabsorption from the ducts determines the concentration of sperm delivered to the ductus epididymidis and is determined by the relative rates of fluid reabsorption and secretion by the duct epithelium. It is interpreted that fluid reabsorption is mainly determined by sodium/hydrogen exchanger 3 (NHE3), an amiloride-sensitive Na ϩ -H ϩ antiport that accounts for 70% of the fluid reabsorbed by the proximal efferent ducts [5,6]. Secretion of fluid into the duct is probably determined by secretion of Cl Ϫ via the cystic fibrosis transmembrane conductance regulator, CFTR [7,8].…”