Regulation of amino acid transporters by glucose and growth factors in cultured primary human trophoblast cells is mediated by mTOR signaling.

Inhibition of mammalian target of rapamycin (mTOR) signaling in cultured human primary trophoblast cells reduces the activity of key placental amino acid transporters. However, the upstream regulators of placental mTOR are unknown. We hypothesized that glucose, insulin, and IGF-I regulate placental amino acid transporters by inducing changes in mTOR signaling. Primary human trophoblast cells were cultured for 24 h with media containing various glucose concentrations, insulin, or IGF-I, with or without the mTOR inhibitor rapamycin, and, subsequently, the activity of system A, system L, and taurine (TAUT) transporters was measured. Glucose deprivation (0.5 mM glucose) did not significantly affect Thr172-AMP-activated protein kinase phosphorylation or REDD1 expression but decreased S6 kinase 1 phosphorylation at Thr389. The activity of system L decreased in a dose-dependent manner in response to decreasing glucose concentrations. This effect was abolished in the presence of rapamycin. Glucose deprivation had two opposing effects on system A activity: 1) an "adaptive" upregulation mediated by an mTOR-independent mechanism and 2) downregulation by an mTOR-dependent mechanism. TAUT activity was increased after incubating cells with glucose-deprived media, and this effect was largely independent of mTOR signaling. Insulin and IGF-I increased system A activity and insulin stimulated system L activity, effects that were abolished by rapamycin. We conclude that the mTOR pathway represents an important intracellular regulatory link between nutrient and growth factor concentrations and amino acid transport in the human placenta.

Airpuff tonometry versus applanation tonometry.

In order to study the reliability of airpuff tonometry, 230 eyes of 115 patients had their IOP measured with 2 airpuff tonometers, NCT and Pulsair, and one applanation tonometer, Perkins handheld Goldmann Type, between Dec 87 and March 89. Each patient had three readings per eye with each airpuff instrument and two readings per eye with the Perkins instrument. Mean age for the group was 68 +/- 11 (SD), range 36-87 years. The mean values were for Perkins: 21.21 +/- 6.27 R.E., 21.28 +/- 5.67 L.E.; for NCT: 21.11 +/- 6.95 R.E., 21.27 +/- 5.41 L.E.; for Pulsair: 23.05 +/- 6.00 R.E., 23.76 +/- 5.39 L.E. The ranges were for Perkins: 9-45 R.E., 9-38 L.E.; for NCT: 8-59 R.E., 11-38 L.E.; for Pulsair: 9-52 R.E., 11-38 L.E. For the Pulsair a value of 18 was found to be a cut-off point below which there were no false negatives, and for the NCT this value was found to be 17. A linear relation between airpuff and applanation tonometry was found, but also a large spread, both for false positives and false negatives.