Na+/K+-ATPase activity and expression in syncytiotrophoblast plasma membranes in pregnancies complicated by diabetes

Many of the transport processes across the Syncytiotrophoblast (ST), such as amino acid transport, are Na⁺-coupled. The maintenance of a low intracellular Na concentration by Na⁺-K⁺-ATPase is therefore crucial for placental transport of nutrients and consequently, foetal growth. In pregnancies complicated by diabetes foetal growth is often accelerated despite rigorous glycemic control of the mother, however the underlying mechanisms are not fully understood. We tested the hypothesis that Na⁺/K⁺-ATPase in ST plasma membranes is up-regulated in diabetic pregnancies associated with accelerated growth. ST microvillous (MVM) and basal (BM) plasma membranes were purified from term placentas of normal pregnancies (control, n=13) and pregnancies complicated by insulin-dependent diabetes mellitus (n=1) or gestational diabetes (n=6). All mothers with diabetes gave birth to large for gestational age babies. The Na⁺/K ⁺-ATPase (α₁-subunit protein expression (Western blot) in MVM and BM was unaltered by diabetes. Na⁺/K ⁺-ATPase activity (K⁺-stimulated, ouabain-sensitive phosphatase activity) in ST plasma membranes was not affected by diabetes. This is the first study of Na⁺/K⁺-ATPase in ST membranes of the human placenta in diabetes. Our data show that accelerated foetal growth in diabetic pregnancies is not associated with elevated ST Na⁺/K ⁺-ATPase protein expression or activity.