CELL SWELLING ACTIVATES PHOSPHOLIPASE A(2) IN EHRLICH ASCITES TUMOR-CELLS

Ehrlich ascites tumor cells, loaded with H-3-labeled arachidonic acid and C-14-labeled stearic acid for two hours, were washed and transferr ed to either isotonic or hypotonic media containing BSA to scavenge th e labeled fatty acids released from the cells. During the first two mi nutes of hypo-osmotic exposure the rate of H-3-labeled arachidonic aci d release is 3.3 times higher than that observed at normal osmolality. Cell swelling also causes an increase in the production of C-14-stear ic acidlabeled lysophosphatidylcholine. This indicates that a phosphol ipase A(2) is activated by cell swelling in the Ehrlich cells. Within the same time frame there is no swelling-induced increase in C-14-labe led stearic acid release nor in the synthesis of phosphatidyl C-14-but anol in the presence of C-14-butanol. Furthermore, U7312, an inhibitor of phospholipase C, does not affect the swelling induced release of C -14-labeled arachidonic acid. Taken together these results exclude inv olvement of phospholipase A(1), C and D in the swelling-induced libera tion of arachidonic acid. The swelling induced release of H-3-labeled arachidonic acid from Ehrlich cells as well as the volume regulatory r esponse are inhibited after preincubation with GDP(beta)S or with AACO CF(3), an inhibitor of the 85 kDa, cytosolic phospholipase A(2). Based on these results we propose that cell swelling activates a phospholip ase A(2)-perhaps the cytosolic 85 kDa type-by a partly G-protein coupl ed process, and that this activation is essential for the subsequent v olume regulatory response.