AJP - Renal Physiology, Vol 264, Issue 5 845-F853, Copyright © 1993 by American Physiological Society
Endothelin activation of phospholipase D: dual modulation by protein kinase C and Ca2+
M. M. Friedlaender, D. Jain, Z. Ahmed, D. Hart, R. L. Barnett and E. P. Nord
Department of Medicine, School of Medicine, Hadassah University Hospital, Jerusalem, Israel.
Previous work from this laboratory has identified an endothelin (ET) type A
(ETA) receptor on cultured rat renal medullary interstitial cells (RMIC),
coupled to phosphatidylinositol-specific phospholipase C (PI-PLC),
dihydropyridine-insensitive receptor-operated Ca2+ channels, and
phospholipase A2. The current studies explored a role for ET stimulation of
phosphatidylcholine-specific phospholipase D (PC-PLD) in intracellular
signaling of this cell type. ET stimulated PLD activation, as measured by
phosphatidic acid (PA) or phosphatidylethanol (PEt) accumulation, in a
time- and concentration-dependent manner. Inhibition of diacylglycerol
(DAG) kinase by ethylene glycol dioctanoate or
6-(2)4-[(4-fluorophenyl)-phenylmethylene]-1-piperadinyl]ethy l-7-methyl-5H
- thiaxolo-[3,2-alpyrimidin]-5-one (R 59022) failed to blunt PA
accumulation, indicating that PLD, and not DAG, was the source of PA.
Inhibition of PA phosphohydrolase (PAP) by propranolol increased late
accumulation of PA, suggesting that the prevailing metabolic flow was in
the direction of PA to DAG. Phorbol 12-myristate 13-acetate (PMA) augmented
ET-evoked PEt accumulation, whereas downregulation of protein kinase C
(PKC) obviated agonist-induced PEt production. PMA augmentation of PLD
activity proceeded independent of cytosolic free Ca2+ concentration. Ca2+
derived from either intracellular or extracellular sources enhanced
ET-related PEt accumulation but was without effect in PKC-downregulated
cells. Collectively, these observations indicate that ET stimulates PLD
production in RMIC. PKC is the major regulator of this process, with Ca2+
playing a secondary, modulatory role. In addition, these data suggest that
PC-PLD is coupled to the ETA receptor.
