Phospholipase C inhibitors and prostaglandins differentially regulate phosphatidylcholine synthesis in rat renal papilla Evidence of compartmental regulation of CTP:phosphocholine cytidylyltransferase and CDP-choline:: 1,2-diacylglycerol cholinephosphotransferase

Phosphatidylcholine (PC) is the most abundant phospholipid in mammalian cell membranes. Several lines of evidence support that PC homeostasis is preserved by the equilibrium between PC biosynthetic enzymes and phospholipases catabolic activities. We have previously shown that papillary synthesis of PC depends on prostaglandins (PGs) that modulate biosynthetic enzymes. In papillary tissue, under bradikynin stimulus, arachidonic acid (AA) mobilization (the substrate for PG synthesis) requires a previous phospholipase C (PLC) activation. Thus, in the present work, we study the possible involvement of PLC in PC biosynthesis and its relationship with PG biosynthetic pathway on the maintenance of phospholipid renewal in papillary membranes; we also evaluated the relevance of CDP-choline pathway enzymes compartmentalization. To this end, neomycin, U-73122 and dibutiryl cyclic AMP, reported as PLC inhibitors, were used to study PC synthesis in rat renal papilla. All the PLC inhibitors assayed impaired PC synthesis. PG synthesis was also blocked by PLC inhibitors without affecting cyclooxygenase activity, indicating a metabolic connection between both pathways. However, we found that PC biosynthesis decrease in the presence of PLC inhibitors was not a consequence of PG decreased synthesis, suggesting that basal PLC activity and PGs exert their effect on different targets of PC biosynthetic pathway. The study of PC biosynthetic enzymes showed that PLC inhibitors affect CTP:phosphocholine cytidylyltransferase (CCT) activity while PGD(2), operates on CDP-choline; 1,2-diacylglycerol cholinephosphotransferase (CPT), both activities associated to papillary enriched-nuclei fraction. The present results suggest that renal papillary PC synthesis is a highly regulated process under basal conditions. Such regulation might occur at least at two different levels of the CDP-choline pathway: on the one hand, PLC operates on CCT activity, on the other, while PGs regulate CPT activity. (C) 2002 Elsevier Science B.V. All rights reserved.