Phospholipase D is activated by G protein and not by calcium ions in vascular smooth muscle.
We assessed the sensitivity of phospholipase D (PLD) activity in vascular smooth muscle to cytosolic Ca2+ by increasing cytosolic Ca2+ levels independently of agonist stimulation. When rat tail artery was preloaded with the Ca2+ indicator fluo 3 pentaacetoxymethyl ester, the addition of high extracellular K+, caffeine, or norepinephrine rapidly enhanced cytosolic Ca2+ levels. Neither increased extracellular K+ nor caffeine addition increased phosphatidylethanol production, indicating that cytosolic Ca2+ elevation alone did not stimulate PLD. In contrast, norepinephrine stimulated phosphatidylethanol production in this tissue. In strips of tail artery permeabilized with alpha-toxin and incubated in solutions containing free Ca2+ concentrations observed during physiological stimulation (pCa 6.4), PLD was not stimulated, whereas incubation with guanosine 5'-O-(3-thiotriphosphate) at pCa 7.0 activated this enzyme. Aluminum fluoride (AlF4-) stimulated PLD, and this activity was insensitive to pertussis toxin after stimulation by either norepinephrine or AlF4-. These results indicate that PLD in vascular smooth muscle is activated by norepinephrine via stimulation of a pertussis toxin-insensitive G protein and not via an increase in intracellular Ca2+ levels.
LaBelle
E F
EF
Bockus Research Institute, Graduate Hospital, Philadelphia, Pennsylvania 19146, USA.
Fulbright
R M
RM
Barsotti
R J
RJ
Gu
H
H
Polyák
E
E
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D004789:Enzyme Activation; D019204:GTP-Binding Proteins / Q000378:metabolism*; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D009638:Norepinephrine / Q000494:pharmacology; D010739:Phospholipase D / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction; D010738:Type C Phospholipases / Q000494:pharmacology; D014662:Vasoconstrictor Agents / Q000494:pharmacology
D014662:Vasoconstrictor Agents; D010738:Type C Phospholipases; D010739:Phospholipase D; D019204:GTP-Binding Proteins; D002118:Calcium; D009638:Norepinephrine