479 IDENTIFICATION OF CALMODULIN IN HUMAN AMNION: ROLE IN PROSTAGLANDIN SYNTHESIS

Abstract

Prostaglandin E₂ (PGE₂) production by human amnion increases with the onset of labor in women and may initiate myometrial contractions at term. Amnion PGE₂ synthesis is Ca²⁺-dependent, but the intracellular mechanism of Ca²⁺ action is obscure. The possibility that the intracellular Ca²⁺ mediator, calmodulin, plays a role in PGE₂ biosynthesis was explored.

Calmodulin-like activity was identified in both the supernatant (cytosol) and pellet (microsomes) fractions of the 105,000×g amnion homogenate as assessed by their ability to stimulate the activity of cAMP phosphodiesterase (PDE). The activity of cytosol protein was greater consistently than that of microsomal protein in paired samples. Removal of Ca²⁺ from the incubation medium by the Ca²⁺ chelator, EGTA, decreased cytosol protein-stimulated PDE activity to basal levels. Three structurally different calmodulin inhibitors, trifluoperazine (TFP), calmidazolium and W7 each inhibited cytosol protein-stimulated PDE activity. The 50% inhibitory concentrations were: calmidazolium (0.11uM), TFP (6.7uM) and W7 (24.0uM). Basal PGE₂ output by dispersed amnion cells was inhibited also by calmidazolium and TFP (calmidazolium > TFP) but not by W7. The Ca²⁺ ionophore, A23187 (10uM), stimulated PGE₂ output, and this was inhibited by TFP. It is concluded that human amnion contains calmodulin which may mediate, in part, Ca²⁺-dependent PGE₂ biosynthesis.

Supported by Canada MRC.

Log in or create a free account to read this content

Gain free access to this article, as well as selected content from this journal and more on nature.com

Access through your institution

or

Sign in or create an account

Continue with Google

Continue with ORCiD