ROLE OF MEMBRANE-ASSOCIATED SERINE ESTERASE IN THE ACTIVATION OF PHOSPHOLIPASE A(2) BY CALCIUM IONOPHORE (A23187) IN PULMONARY ARTERIAL SMOOTH-MUSCLE CELLS

Exposure of rabbit pulmonary arterial smooth muscle cells to 10 mu M o f the calcium ionophore A23187 dramatically stimulates cell membrane-a ssociated phospholipase A(2) activity and arachidonic acid release. In addition, A23187 also enhances cell membrane-associated serine estera se activity. Serine esterase inhibitors phenylmethylsulfonylfluoride a nd diisopropyl fluorophosphate prevent the increase in serine esterase and phospholipase A(2) activities and arachidonic acid release caused by A23187. A23187 still stimulated serine esterase and phospholipase A(2) activities and arachidonic acid release in cells pretreated with nominal Ca2+ free buffer. Treatment of the cell membrane with A23187 d oes not cause any appreciable change in serine esterase and phospholip ase A(2) activities. Pretreatment of the cells with actinomycin D or c ycloheximide did not prevent the increase in the cell membrane associa ted serine esterase and phospholipase A(2) activities, and arachidonic acid release caused by A23187. These results suggest that (i) a membr ane-associated serine esterase plays an important role in stimulating the smooth muscle cell membrane associated phospholipase A(2) activity (ii) in addition to the presence of extracellular Ca2+, release of Ca 2+ from intracellular storage site(s) by A23187 also appears to play a role in stimulating the cell membrane-associated serine esterase and phospholipase A(2) activities, and (iii) the increase in the cell memb rane-associated serine esterase and phospholipase A(2) activities does not appear to require new RNA or protein synthesis.