Mechanisms of electrolyte transport across the endometrium. I. Regulation by PGF2 alpha and cAMP

Abstract

The purpose of this study was to characterize the transport mechanisms in endometrial epithelial cells that are responsible for regulation of Na and K concentrations in uterine luminal fluid. Porcine endometrial tissues were mounted in Ussing chambers and bathed in plasmalike Ringer solution. The mean basal short-circuit current (Isc) was 40 microA/cm2, and the mean tissue conductance was 3.6 mS/cm2. Addition of amiloride to the luminal solution inhibited 86% of the basal Isc. Concentration-response experiments using amiloride analogues showed a rank order of potency of benzamil > amiloride > 5-(N-methyl-N-isobutyl)-amiloride in blocking the Isc, with no response to ethylisopropylamiloride. Na channel immunoreactivity was localized to the apical membrane of surface epithelial cells. The Na-to-K selectivity ratio of the amiloride-sensitive Na channel was calculated to be 6.4:1. Prostaglandin (PG) F2 alpha or 8-(chlorophenylthio)-adenosine 3',5'-cyclic monophosphate (CPT-cAMP) added to the luminal solution stimulated a twofold increase in Isc that was inhibited by pretreatment with amiloride. Experiments using both amphotericin B-permeabilized tissues and intact tissues showed that PGF2 alpha and cAMP increased Na absorption by activation of basolateral K channels. Treatment of the luminal solution with 4-aminopyridine produced an effect on Isc that was consistent with block of K secretion and a subsequent decrease in Na absorption. These experiments showed that Na and K transport are tightly coupled processes occurring under basal conditions in surface endometrial epithelial cells and that these processes are regulated by PGF2 alpha and cAMP.

Sodium and anion transport across the avian uterine (shell gland)epithelium

“…This result was consistent with previous studies of Na + transport across the porcine, murine and human endometrial epithelium (Vetter and O'Grady, 1996;Deachapunya et al, 1999;Palmer-Densmore et al, 2002;Chan et al, 2001;Matthews et al, 1998). In native porcine endometrial tissues mounted in Ussing chambers, the surface epithelial cells exhibited a basal I sc that was blocked by amiloride with an IC 50 value (0.8·µmol·l -1 ) identical to that reported for the shell gland epithelium in this study (Vetter and O'Grady, 1996). Similar effects of amiloride and benzamil on basal I sc were reported for cultured porcine glandular endometrial epithelial cells maintained under serum-free conditions (Deachapunya et al, 1999).…”

“…The observation that amiloride and benzamil produced inhibition of the basal I sc and that this decrease in current was associated with inhibition of the apical-tobasolateral and net Na + flux strongly suggested that ENaC Na + channels were involved in Na + absorption across this epithelium. This result was consistent with previous studies of Na + transport across the porcine, murine and human endometrial epithelium (Vetter and O'Grady, 1996;Deachapunya et al, 1999;Palmer-Densmore et al, 2002;Chan et al, 2001;Matthews et al, 1998). In native porcine endometrial tissues mounted in Ussing chambers, the surface epithelial cells exhibited a basal I sc that was blocked by amiloride with an IC 50 value (0.8·µmol·l -1 ) identical to that reported for the shell gland epithelium in this study (Vetter and O'Grady, 1996).…”

“…Similar effects of amiloride and benzamil on basal I sc were reported for cultured porcine glandular endometrial epithelial cells maintained under serum-free conditions (Deachapunya et al, 1999). Analysis of tissue morphology (Fig.·1) indicated the presence of lamellae that were clearly distinct from the mucosal morphology of mammalian endometrium (Vetter and O'Grady, 1996). Whether Na + absorption and anion secretion are associated with separate cell types within the shell gland epithelium is unknown at this time.…”

“…Stimulation of Cl -secretion by 8-cpt cAMP was previously reported in cultured mammalian endometrial epithelial cells (Deachapunya and O'Grady, 1998). However, native porcine endometrial tissues mounted in Ussing chambers and treated with 8-cpt cAMP or with PGF2α, produced a sustained increase in amiloride-sensitive Na + absorption (Vetter and O'Grady, 1996;Vetter et al, 1997). This increase in Na + transport was not associated with an increase in apical Na + conductance, but appeared to be the result of an increase in driving force for apical Na + uptake produced by activation of basolateral K + channels (Vetter et al, 1997).…”

Regulation of electrolyte transport across cultured endometrial epithelial cells by prolactin

“…The transport-related activities of the surface and glandular epithelial cells have been shown to be regulated by several hormones, growth factors, cytokines, and a number of signaling molecules. Electrophysiological studies of cultured human endometrial epithelial cells (Matthews et al 1993) and the intact porcine endometrial epithelium (Vetter & O'Grady 1996) have provided direct evidence for the regulation of Na C absorption and K C secretion. In the primary culture of mouse and porcine endometrial epithelial cells, prostaglandins (PGs) especially PGE2, adrenaline, ATP, and UTP were found to activate anion secretion (Chan et al 1997, Fong et al 1998, Deachapunya & O'Grady 1998, Palmer-Densmore et al 2002.…”