Vesicle-mediated phosphatidylcholine reapposition to the plasma membrane following hormone-induced phospholipase D activation

Phospholipase D (PLD) activation involved in signal transduction may lead t o the hydrolysis of conspicuous amounts of phosphatidylcholine (PC), This s tudy shows that PLD activation significantly alters the plasma membrane (PM ) environment and the membrane exchange dynamics, PC-PLD activation in vaso pressin (AVP)-stimulated L6 myogenic cells was accompanied by increased exo cytosis and decreased membrane fluidity, as shown by transmission EM and fl uorescence spectroscopy of trimethylammonium-diphenyl-hexatriene. AVP-induc ed exocytosis appeared to be brefeldin A-insensitive. PLD inhibition by Zn2 + and PC de novo synthesis inhibition by hexadecylphosphocholine abolished AVP-induced vesicle traffic. Upon AVP stimulation, metabolically labeled PC decreased in PM, then transiently increased in microsomes, and returned to the prestimulus level in the PM within 5 min, a phenomenon requiring PC ne osynthesis and microtubule functionality. Vesicle traffic with similar feat ures was also observed after endothelin-1-induced PC-PLD activation in rat peritubular myoid cells. These results indicate that, in nonsecretory cells , exocytosis coupled to PC de novo synthesis restores PM-PC, conspicuously consumed during PLD-mediated signal transduction. (C) 2000 Academic Press.