Na Absorption Across Endometrial Epithelial Cells is Stimulated by cAMP-dependent Activation of an Inwardly Rectifying K Channel

Abstract

Previous studies in our laboratory have shown that Na absorption across the porcine endometrium is stimulated by PGF2alpha and cAMP-dependent activation of a barium-sensitive K channel located in the basolateral membrane of surface epithelial cells. In this study, we identify and characterize this basolateral, barium-sensitive K conductance. Porcine uterine tissues were mounted in Ussing chambers and bathed with KMeSO4 Ringer solution. Amphotericin B (70 microM) was added to the luminal solution to permeabilize the apical membrane and determine the current-voltage relationship of the basolateral K conductance after activation by 100 microM CPT-cAMP. An inwardly rectifying current was identified which possessed a reversal potential of -53 mV when standard Ringer solution was used to bathe the serosal surface. The K:Na selectivity ratio was calculated to be 12:1. Administration of 5 mM barium to the serosal solution completely inhibited the current activated by cAMP under these conditions. In addition to these experiments, amphotericin-perforated whole cell patch clamp recordings were obtained from primary cultures of porcine surface endometrial cells. The isolated cells displayed an inwardly rectifying current under basal conditions. This current was significantly stimulated by CPT-cAMP and blocked by barium. These results together with our previous studies demonstrate that cAMP increases Na absorption in porcine endometrial epithelial cells by activating an inwardly rectifying K channel present in the basolateral membrane. Similar patch clamp experiments were conducted using cells from a human endometrial epithelial cell line, RL95-2. An inwardly rectifying current was also identified in these cells which possessed a reversal potential of -56 mV when the cells were bathed in standard Ringer solution. This current was blocked by barium as well as cesium. However, the current from the human cells did not appear to be activated by cAMP, indicating that distinct subtypes of inwardly rectifying K channels are present in endometrial epithelial cells from different species.

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

“…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).…”

“…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). Decreases in eggshell quality resulting from a reduction in shell thickness is a well-known problem in egg production (Bahr and Palmer, 1989;Bennett, 1992;Hughes et al, 1986;Joyner et al, 1977;Poggenpoel, 1986;Soares et al, 1988).…”

Treatment of Human Endometrial Gland Epithelial Cells with Chorionic Gonadotropin/Luteinizing Hormone Increases the Expression of the Cyclooxygenase-2 Gene

“…These are, for example, the synthesis and/or secretion of glycodelin, insulin-like growth factor binding protein-1 (43), GnRH (44), and vascular endothelial growth factor (45); the secretion of fluids and electrolytes (46,47); etc. There is evidence for PGE 2 and cAMP regulating some of these functions (46,47). By increasing PGE 2 and cAMP levels, hCG may also regulate these and other endometrial functions.…”

Chloride and potassium channel function in alveolar epithelial cells

“…Inhibition of these K ϩ channels effectively blocks transepithelial Cl Ϫ secretion. K ϩ channels also play a similar role in Na ϩabsorbing epithelia, where K ϩ exit helps to offset membrane depolarization produced by electrogenic Na ϩ influx (8,85,86). At this time, an extensive literature on the identity and function of K ϩ channels in alveolar epithelial cells is not available.…”