Gestational changes in electrolyte transport, electrical activity, and permeability of the porcine placenta

Abstract

1. The electrolyte transport capacities of the porcine placenta and fetal membranes (amnion, chorion, and allantois) during gestation (47-112 days) were assessed in vitro and in the absence of electrochemical, osmotic, or hydrostatic driving forces. Net transmural transport of 22Na and 36Cl across sections of porcine allantochorion-endometrium (ALCE), amniochorion-endometrium (AMCE), and allantoamnion (AA) mounted in Ussing chambers could not be detected at any stage of gestation. 2. These tissues were characterised throughout gestation by low electrical potential difference (PD; less than 5 mV, fetal side positive with respect to maternal side) and short circuit current (SCC; less than 16 microA.cm-2) which were amiloride and iodoacetate sensitive. 3. A periparturitent reversal in the polarity of PD to fetal side negative and a change in the direction of the SCC was observed in tissues obtained from sows (n = 3) at 111-112 day gestation. These changes were accompanied by a 73% increase in electrical resistance (R) and a 2-10-fold decrease in the permeability of tissues to Na and Cl. 4. Morphological studies revealed a decrease in the thickness of allantoamnion and a decrease in the height of epithelia from ALCE, AMCE, and AA during gestation, indicating a decrease in activity. These morphological changes only partly explained the pre-term electrophysiological changes in these tissues.

Sodium transport across the chorioallantoic membrane of porcine placenta involves the epithelial sodium channel (ENaC)

“…In contrast, Sibley et al (1986) using chorioallantoic membrane with endometrium still attached observed PD with polarity fetal side positive with respect to maternal, and I sc with positive current flowing from mother to fetus. Using a similar preparation and tissues taken from sows between 47 and 109 days gestation, Rice and colleagues (1991) observed polarities similar to those reported by Sibley et al ( 1985). In their study PD and I sc values ranged from −0.1 mV and −2.6 μA cm −2 in early gestation to −4.9 mV and −8.2 μA cm −2 at day 109.…”

“…They also observed that the allantoic membrane, when isolated from the trophoblast, was freely permeable to both Na + and chloride (Cl − ) and was electrically neutral. It has been observed that both the PD and I sc associated with the endometrial‐chorioallantoic membrane is sensitive to 1 m m amiloride when placed on both sides (Rice et al 1991). The decline in these parameters was gradual, taking 5–8 min to produce maximum effect.…”

“…The decline in these parameters was gradual, taking 5–8 min to produce maximum effect. It has not been possible to detect net movements of Na + under basal conditions using 22 Na (Rice et al 1991).…”

Site of catecholamine modulation of feto‐maternal electric potential difference in the pig

“…In vitro approaches have been used in an attempt to clarify this point. Measurements for both PD and short circuit current have been obtained from pig placenta mounted in Ussing chambers (Crawford & McCance, 1960;Bazer, Goldstein & Barron, 1981; Glazier, Moore & Rice, Dantzer, Madsen & Skadhauge, 1991). It should be noted that the two earlier reports give different values from the two more recent studies which show good agreement.…”

Regulation of water and solute transport across mammalian plasma cell membranes by prolactin

“…With this technique, the amnion from a number of species has been shown to be permeable to water and ions (e.g. see Page et al 1974;North & Segal, 1976;Wintour et al 1988;Rice et al 1991).…”