Phospholipase C activity in human placental membrane.

Receptor-stimulated hydrolysis of polyphosphoinositides by action of phospholipase C appears to be an important mediator of cell activation through the generation of the second messengers, in particular inositol triphosphate (IP3). In order to understand placental function better, activity of IP3 production from membrane in cell-free system was examined. Incubation of membrane preparation from [3H]inositol-labelled human placenta with Ca2+ in the presence of 1 mM ATP and 1 mM GTP resulted in the rapid production of IP3 in a dose dependent manner; half-maximal effect occurred at 10 microM. On the other hand, little effect was observed in the case of membrane prepared from [3H]arachidonic acid-labelled placenta, suggesting higher requirement of Ca2+ for phospholipase A2 activation. These data suggest that placenta contains phospholipase C hydrolyzing polyphosphoinositide at physiological concentration of Ca2. This is the first report to provide direct evidence of transmembrane signalling mechanisms in the human placenta, and may provide a clue to the etiology of placental disorders.