Differences in phospholipid incorporation of 32P relevant to alpha 1-receptor coupling events in rat and rabbit aorta

Labelling of membrane phospholipids with 32P was compared in rat and rabbit aorta under basal conditions and during alpha 1-receptor stimulation. Incorporation of 32P proceeded at a significantly higher rate in rat tissue. The ratio of basal labelling following 30 min of incubation for rat/rabbit arteries was 4.8 for phosphatidylinositol diphosphate (PIP2), 6.0 for phosphatidylinositol phosphate (PIP), 9.0 for phosphatidylinositol (PI), 6.0 for phosphatidic acid (PA) and 18.7 for phosphatidylcholine (PC). Addition of 10(-5)M norepinephrine (NE) to labelled tissues resulted in a similar decrease in [32P]-PIP2 in both rat and rabbit tissues. Greater percent increases were seen in rabbit tissue of [32P]-PA (4-6 fold), and [32P]-PI (3-5 fold), when measured over the initial 10 minutes of agonist exposure. While NE caused a gradual increase of 32P incorporation into PC in rabbit aorta, reaching 180% above control after 10 minutes, PC labelling was not increased in rat aorta. Our findings provide evidence for the enhanced labelling of rat vs rabbit aorta phospholipids. This may account for differences in receptor responses and associated Ca+ movements which have been previously recognized to exist between aorta of these two species.