Apical ANG II-stimulated PLA(2) activity and Na+ flux: a potential role for Ca2+-independent PLA(2)

Type 1 angiotensin II (ANG II) receptors (AT(1)R), which mediate proximal tubule (PT) salt and water reabsorption, undergo endocytosis and recycling. Prior studies in a PT-Like model (LLC-PKC14 cells expressing rabbit AT(1)R) (LLC-PK-AT(1)R cells) determined that quinacrine, a nonspecific phospholipase A(2) (PLA(2)) inhibitor, and the haloenol lactone suicide substrate (HELSS), a Ca2+-independent PLA(2) inhibitor, attenuated apical (AP) AT(1)R recycling. Further studies were undertaken to examine the association between AT(1)R endocytotic movement and PLA(2) activity in this model. AP ANG II (100 nM) increased [H-3]arachidonic acid ([H-3]AA) release 4.4 +/- 0.38-fold in LLC-PK-AT(1)R cells cultured on permeable supports. Basolateral (BL) ANG II had no significant effect. Reversed-phase high-performance liquid chromatography confirmed that AP ANG II stimulated free [H-3]AA release. Quinacrine, HELSS, and palmitoyl trifluoromethyl ketone, another Ca2+-independent PLA(2) inhibitor, inhibited AP ANG II-stimulated [H-3]AA release, as did inhibiting AP AT(1)R internalization with phenylarsine oxide. The role of HELSS-inhibitable AA release in ANG II-mediated Na-22 flux was examined, given the effects of AT(1)R-mediated PLA(2) activity on salt and water reabsorption. AP ANG II (100 nhl) stimulated Na-22 flux (AP --> BL), a response inhibited by HELSS. Thus, in this model, AP AT(1)R activated PLA(2) with concomitant Na-22 flux (AP --> BL), suggesting a link between AP AT(1)R endocytotic movement; AT(1)R-stimulated PLA(2) activity, and Na-22 flux in this model. The effects of HELSS suggest that Ca2+-independent PLA(2) activity may be involved in this AP ANG II response.