Phospholipase activity in permeabilized platelets: evidence that
pla2, plc and pld are not essential to exocytosis.
Coorssen, Jens R.
Department of Pathology, McMaster University, Hamilton, Ontario,
Canada L8N 3Z5
APStracts 2:0395C, 1995.
Numerous studies have identified phospholipase metabolites as membrane
fusogens, and phospholipase D (PLD) (Coorssen and Haslam, FEBS Lett.
316: 170-174, 1993), C (PLC) and A2 (PLA2) activities correlate with
secretion. Do these enzymes have essential or modulatory roles? This
study confirms that secretion does not require Ca2+ or PLC (Coorssen
et al., Cell Regulation 1: 1027-1041, 1990). Arachidonic acid (AA),
phosphatidic acid (PA) or analogues, exogenous metabolites of PLA2
and PLD, were tested in electropermeabilized human platelets. AA
potentiated GTP[tau]S-induced secretion; eicosanoids were not
essential. Endogenous [3H]AA formation correlated with GTP[tau]S
-induced secretion, and PMA promoted these effects. Inhibitors were
used to probe phospholipase influences on secretion. Only PLD
inhibitors blocked secretion. However, PMA blocked inhibition of PKC
and secretion by quercetin suggesting that PA formed by PLD supports
PKC activation and GTP[tau]S-induced secretion. Thus, PA analogues
had no effect alone but enhanced GTP[tau]S-induced PKC activity and
secretion. Slower PLD activation compared to secretion also indicates
a nonessential role. This is the first report of a Ca2+-independent
PLA2 activity in human platelets, use of quercetin as a PLD
inhibitor, and dissociation of PLA2, PLC and PLD activities from
secretion. No major phospholipase activities are essential to the
final steps in exocytosis but modulatory roles are indicated.
Received 27 June 1995; accepted in final form 27 October 1995.
APS Manuscript Number C378-5.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 30 November 95