Cyclic adenosine-3',5'-monophosphate alters hydrolysis of phospholipids by mouse embryo palate mesenchyme cells

The purpose of this study was to determine whether inhibition of release of arachidonic acid from mouse embryo palate mesenchyme (MEPM) cells in response to cAMP is due to a selected or generalized inhibition of hydrolysis of esterified pools of arachidonic acid. The calcium ionophore A23187 proved to be a useful probe of phospholipid hydrolases in MEPM cells, since it stimulated release of radiolabeled fatty acids from phospholipids of prelabeled MEPM cells as a function of the length of exposure, concentration, and concentration of Ca2+ in the medium. Elevation of intracellular levels of cAMP by treatment with (-) isoproterenol resulted in the inhibition of release of radiolabeled arachidonic acid in response to A23187. Analysis by quantitative gas-liquid chromatography revealed the source of the arachidonic acid released in response to the ionophore to be 1,2-diradyl-sn-glycero-3-phosphoethanolamine; elevation of intracellular levels of cAMP inhibited hydrolysis of this substrate, but may have stimulated hydrolysis of 1,2-diradyl-sn-glycero-3-phosphocholine. These findings permit the conclusions that 1) the ionophore stimulates activities of selected phospholipases A in MEPM cells and 2) cAMP modulates certain phospholipases A in MEPM cells in a specific manner.     

Metabolism of prostaglandin E2 by mouse embryo palate mesenchyme cells in vitro

Mouse embryo palate mesenchyme cells synthesize a number of prostaglandins, particularly prostaglandin E2 (PGE2). However, the ability of such cells to metabolize prostaglandins was unknown. By use of radiolabeled PGE2 we determined that palate mesenchyme cells have little ability to degrade that prostaglandin in vitro but are able to metabolize products formed from its spontaneous degradation.     

ULTRASTRUCTURAL CHANGES OF MEMBRANES WITH HYDRATION IN SOYBEAN SEEDS

Structural changes of soybean seeds at various levels of hydration were examined for possible explanations of the rapid initial leakage of solutes during imbibition. A clustering of vesicles and lipid bodies was observed along the two types of membranes which must undergo most extensive enlargement: the plasmalemma and the protein bodies. There was no such association with the membranes of nuclei, plastids, and mitochondria. Freeze fracture replicas of tissue with less than about 18% water content yielded only small areas identifiable as plasma membrane and these contained many irregularities or pock marks. As imbibition proceeded, larger expanses of plasma membrane were revealed. The increase in water content was seen to remove the irregularities of the membrane plane, and generally was associated with an extensive increase in particles embedded in the membrane sheets. It is suggested that imbibition may involve rapid and extensive incorporation of new materials into expanding membranes of the cell, including addition of lipids and possibly of proteins.