Cytoskeleton-dependent endocytosis is required for apical type 1 angiotensin II receptor-mediated phospholipase C activation in cultured rat proximal tubule cells

Abstract

Renal proximal tubule sodium reabsorption is enhanced by apical or basolateral angiotensin II (All). Although All activates phospholipase C (PLC) in other tissues, All coupling to PLC on either apical or basolateral surfaces of proximal tubule cells is unclear. To determine if All causes PLC activation, and the differences between apical and basolateral All receptor function, receptors were unilaterally activated in rat proximal tubule cells cultured on permeable, collagen-coated supports. Apical All incubation resulted in concentration- and time-dependent inositol trisphosphate (IP3) formation. Basolateral All caused greater IP3 responses. Apical All-induced IP3 generation was inhibited by DuP 753, suggesting that the type 1 All receptor subtype mediated proximal tubule PLC activation. Apical All signaling did not result from para cellular ligand leak to basolateral receptors since All-induced PLC activation occurred when basolateral All receptors were occupied by SarLeu All or DuP 753. Inhibition of endocytosis with phenylarsine oxide prevented apical (but not basolateral) All-induced IP3 formation. Cytoskeletal disruption with colchicine or cytochalasin D also prevented apical All-induced IP3 generation. These results demonstrate that in cultured rat proximal tubule cells, All is coupled to PLC via type 1 All receptors and cytoskeleton-dependent endocytosis is required for apical (but not basolateral) All receptor-mediated PLC activation.