Na+ transport, H+ concentration gradient dissipation, and system A amino acid transporter activity in purified microvillous plasma membrane isolated from first-trimester human placenta: comparison with the term microvillous membrane.
Our purpose was to isolate microvillous plasma membrane from first-trimester placenta and to measure its transport properties with regard to Na+, H+, and a neutral amino acid. Microvillous membrane was isolated from first-trimester (10 to 13 weeks) and term (38 to 42 weeks) placenta and the purity determined. Uptake of 22Na+ was measured in the presence of an outwardly directly H+ gradient in the presence or absence of amiloride (0.5 mmol/L). The rate of dissipation of an H+ concentration gradient was determined with the H(+)-sensitive fluorescent probe 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein. 14C-methylaminoisobutyric acid uptake was measured in the presence and absence of an inwardly directed Na+ gradient. Purity, vesicle volume, vesicle orientation, and electron micrographic appearance of the first-trimester membranes were similar to those obtained from term placenta, but vesicle protein recovery was lower. Amiloride-sensitive Na+ uptake and Na(+)-dependent 14C-methylaminoisobutyric acid uptake was threefold to fourfold lower by first-trimester than by term membranes. The rate of H+ concentration gradient dissipation was greater in the former. The first-trimester microvillous membrane has similar general characteristics to that from term placenta, but its transport activity is quite different.
Mahendran
D
D
Action Research Placental and Perinatal Unit, University Department of Child Health, St. Mary's Hospital, Manchester, United Kingdom.
Byrne
S
S
Donnai
P
P
D'Souza
S W
SW
Glazier
J D
JD
Jones
C J
CJ
Sibley
C P
CP
D026905:Amino Acid Transport Systems; D000621:Aminoisobutyric Acids / Q000493:pharmacokinetics; D001692:Biological Transport; D002352:Carrier Proteins / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D005260:Female; D006801:Humans; D006859:Hydrogen / Q000378:metabolism*; D008871:Microvilli / Q000378:metabolism; D009994:Osmolar Concentration; D010920:Placenta / Q000378:metabolism*; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D011263:Pregnancy Trimester, Third; D012964:Sodium / Q000378:metabolism*
D026905:Amino Acid Transport Systems; D000621:Aminoisobutyric Acids; D002352:Carrier Proteins; C017911:2-(methylamino)isobutyric acid; D006859:Hydrogen; D012964:Sodium