Effect of (1-34) parathyroid hormone-related peptide on the composition and turnover of phospholipids in syncytiotrophoblast brush border and basal plasma membranes of human placenta.

ABSTRACT

The effect of parathyroid hormone-related peptide on the lipid composition and the turnover of phosphoinositides was studied in brush border and basal plasma membranes of human placenta syncytiotrophoblasts. Lipid composition of the two polar membranes differed markedly with respect to the cholesterol/phospholipid ratio (0.57 +/- 0.04 and 0.91 +/- 0.05 in basal plasma membranes and brush border membranes, respectively). Sphingomyelin was the major phospholipid in both membranes. Except for the phosphoinositide-phosphatidylserine complex which was higher in basal plasma membranes, the phospholipid composition was comparable in the brush border membrane and basal plasma membranes. Incubation of the tissue with 10(-8) M parathyroid hormone-related peptide (1-34) resulted in a significant increase in the phosphatidylinositol phosphate content of the two membranes and in the phosphatidylinositol biphosphate concentration in the basal plasma membranes. Finally, when the tissue was preincubated with [3H]myo-inositol in the presence of 10(-8) M parathyroid hormone-related peptide (1-34), the hormone significantly stimulated the inositol phosphate release by the two membranes. These results demonstrate that (1) in the placental syncytiotrophoblast, as found in other transport epithelia, the lipid composition of the polar membranes is different; (2) parathyroid hormone-related peptide stimulates the phosphoinositide turnover in both membranes.