Phospholipase d is activated by g protein and not by calcium ions in vascular smooth muscle. Labelle, Edward F., Robert Fulbright, Robert J. Barsotti, Hong Gu, and Erzs[acute]ebet Poly[acute]ak. BOCKUS RESEARCH INSTITUTE THE GRADUATE HOSPITAL 415 S. 19TH ST. PHILADELPHIA, PA 19146
APStracts 2:0554H, 1995.
We assessed the sensitivity of phospholipase D activity in vascular smooth muscle to cytosolic calcium by increasing cytosolic calcium levels independently of agonist stimulation. When rat tail artery was preloaded with the calcium indicator Fluo-3AM, the addition of high extracellular K+, caffeine, or norepinephrine rapidly enhanced cytosolic calcium levels. Neither increased extracellular K+ nor caffeine addition increased phosphatidylethanol production, indicating that cytosolic calcium elevation alone did not stimulate phospholipase D. In contrast, norepinephrine stimulated phosphatidylethanol production in this tissue. In strips of tail artery permeabilized with [alpha] toxin and incubated in solutions containing free calcium concentrations observed during physiological stimulation (pCa=6.4), phospholipase D was not stimulated, while incubation with GTP[gamma]S at pCa 7.0 activated this enzyme. Aluminum fluoride stimulated phospholipase D and this activity was insensitive to pertussis toxin after stimulation by either norepinephrine or aluminum fluoride. These results indicate that phospholipase D in vascular smooth muscle is activated by norepinephrine via stimulation of a pertussis toxin-insensitive G protein and not via an increase in intracellular calcium levels. 

Received 21 October 1994; accepted in final form 28 August 1995.
APS Manuscript Number H939-4.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 23 December 95