Regional Differences in Bioelectrical Properties and Anion Secretion in Cultured Epithelia from Rat and Human Male Excurrent Ducts1

Abstract

Bioelectrical properties and anion secretion in cultured epithelia from different regions of rat and human male excurrent ducts were studied by measuring the short-circuit currents (ISC). In all regions of the rat excurrent duct, Cl- secretion accounts for over 90% of the basal ISC, although the magnitude varied in different regions. Cl- secretion was found to be mediated by a Cl-/HCO3- exchanger, an Na+/H+ exchanger, and an Na+/K+/2Cl- symport located on the basolateral side of the epithelial cells. Forskolin, an activator of adenylate cyclase, and ionomycin, a Ca2+ ionophore, were used to investigate the relative importance of cAMP and Ca2+ as intracellular messengers regulating Cl- secretion in different regions. It was found that in both species, the forskolin-evoked ISC response was larger in the proximal end (efferent duct/caput epididymidis [rat/human, respectively]) than in the distal end (cauda/corpus epididymidis). The response to ionomycin in the rat cauda epididymidis (distal end) was larger than that in the efferent duct (proximal end); on the other hand, no significant difference in the ionomycin-induced ISC was observed in the caput and the corpus regions from the human epididymis. Our results indicate that while the cAMP- and Ca(2+)-dependent pathways are both involved in regulating Cl- secretion in all regions along the male excurrent ducts in both species, a regional difference exists with respect to the relative importance of the two regulatory pathways involved in Cl- secretion along the male reproductive tract.

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

“…The proportion of water and solute reabsorption which was not inhibited by amiloride in this study and in the proximal tubule (Chantrelle et al 1985) is probably due to a substantial reabsorption by passive diffusion through the paracellular pathway. This proposal is supported by ultrastructural findings (Suzuki & Nagano, 1978), measurements of low electrical resistance across cultured efferent duct epithelium (Chan et al 1995) and the apparently rapid equilibration of electrolyte concentrations across the epithelium in situ (Clulow et al 1994(Clulow et al , 1996. The effect of Na¤-H¤ exchange on luminal pH was not examined in this study, but will need to be the subject of future investigation.…”

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

“…Indeed, it seems that K ϩ reabsorption is completely inhibited by (high) levels of db-cAMP that support net reabsorption of Cl Ϫ ( Table 1). The increased concentration of Cl Ϫ in the collectates can be explained by cAMP stimulation of Cl Ϫ secretion in the efferent ducts (see above) as in other tissues including the cauda epididymidis [49,50] respiratory epithelium [39,51] and small and large intestine [52]. In the absence of db-cAMP in the perfusate, Cl Ϫ reabsorption in the efferent ducts is so much greater than secretion that there is no obvious movement of Cl Ϫ into the lumen when net transport is determined (Table 1).…”

Estrogen Regulation of Ion Transporter Messenger RNA Levels in Mouse Efferent Ductules Are Mediated Differentially Through Estrogen Receptor (ER) α and ERβ1

“…Located in the cytoplasm, NHE2 had no apparent role, but it may be involved in controlling endosomal intracellular pH [13]. Although greater than 95% of fluid and electrolytes are reabsorbed by the ED, the secretion of bicarbonate and chloride anions into the lumen (HCO 3 Ϫ and Cl Ϫ ) has been documented in the ED [16,17]. Leung et al [13] suggested that in concert, basolaterally located Na ϩ -K ϩ ATPase, NHE1, Na ϩ /K ϩ /2Cl Ϫ cotransporter, and a basolateral K ϩ channel support the accumulation of Cl Ϫ and HCO 3 Ϫ within the cell.…”