Table No. 1.

Phospholipase A₂ (PLA₂) activity (nmol.mg protein⁻¹.min⁻¹) in membrane and cytosolic subcellular fractions from human lung microvascular endothelial cells under control conditions or stimulated with thrombin (0.1 IU/ml, 5 mins) or tryptase (20 ng/ml, 5 mins). Where appropriate, cells were pretreated with bromoenol lactone (BEL, 2 µM, 10 mins) or arachidonyl trifluoromethyl ketone (AACOCF₃, 5 µM, 10 mins) prior to thrombin or tryptase stimulation. PLA₂ activity was measured using (16:0, [³H]18:1) plasmenylcholine substrate in the absence (4 mM EGTA) or presence (1 mM Ca²⁺) of calcium. Values represent mean ± SEM for separate measurements from 3 different cell isolations.

Cell Fraction		EGTA	Ca2+	EGTA	Ca2+	EGTA	Ca2+
				BEL	BEL	AACOCF3	AACOCF3
Membrane	Control	4.22 ± 0.16	4.56 ± 0.21	1.81 ± 0.12	1.72 ± 0.21	4.19 ± 0.21	4.33 ± 0.31
	Thrombin	8.78 ± 0.34	9.13 ± 0.57	3.11 ± 0.31	2.95 ± 0.37	7.94 ± 0.52	8.03 ± 0.41
	Tryptase	8.19 ± 0.48	8.56 ± 0.41	2.78 ± 0.42	2.56 ± 0.18	8.31 ± 0.47	8.55 ± 0.18
Cytosol	Control	0.42 ± 0.05	0.51 ± 0.06	0.19 ± 0.04	0.21 ± 0.04	0.29 ± 0.05	0.31 ± 0.08
	Thrombin	0.48 ± 0.12	0.51 ± 0.12	0.22 ± 0.02	0.16 ± 0.03	0.32 ± 0.04	0.31 ± 0.09
	Tryptase	0.45 ± 0.09	0.53 ± 0.12	0.17 ± 0.02	0.23 ± 0.02	0.29 ± 0.03	0.27 ± 0.05