Calcium-independent phospholipase A2 in rabbit ventricular myocytes

We have previously reported that the majority of phospholipase A(2) (PLA(2)) activity in rabbit ventricular myocytes is membrane-associated, calcium-independent (iPLA(2)), selective for arachidonylated plasmalogen phospholipids and inhibited by the iPLA(2)-selective inhibitor bromoenol lactone (BEL). Here, we identified the presence of iPLA(2) in rabbit ventricular myocytes, determined the full length sequences for rabbit iPLA(2)beta and iPLA(2)gamma and compared their homology to the human isoforms. Rabbit iPLA(2)beta encoded a protein with a predicated molecular mass of 74 kDa that is 91% identical to the human iPLA(2)beta short isoform. Full length iPLA(2)gamma protein has a predicated molecular mass of 88 kDa and is 88% identical to the human isoform. Immunoblot analysis of iPLA(2)beta and gamma in membrane and cytosolic fractions from rabbit and human cardiac myocytes demonstrated a similar pattern of distribution with both isoforms present in the membrane fraction, but no detectable protein in the cytosol. Membrane-associated iPLA(2) activity was inhibited preferentially by the R enantiomer of bromoenol lactone [(R)-BEL], indicating that the majority of activity is due to iPLA(2)gamma.