Neurokinin-1 (substance p) receptor mediated inhibition of endosomal fusion in transitional epithelial cells during acute urinary bladder inflammation

Inlravesical infusion of ovalbumin antigen into pre-sensitized guinea pigs stimulates rapid development of bladder inflammation. Reversal of inflammatory edema, mast cell infiltrate and neutrophil accumulation with neurokinin-I and bradykinin antagonists suggests these peptides are important mediators of this process. Vacuolization of the subapical endosomal compartment of the transition epithelial cells lining the bladder suggests that the inflammatory response includes changes in endosomal trafficking and fusion. To directly test for changes in endosomal fusion associated with inflammation we reconstituted fusion of transitional cell endosomes in vitro using both cuvette based and flow cytontctry energy transfer assays. Bladders were loaded with fluorescent dyes by a hypotonie withdrawal protocol before endosomal isolation by gradient centrifugation (AJP 267:CI483-1492, 1994). Compared to control bladders (27.8±3.9, n=4 arbitrary fluorescent units) endosomal fusion is inhibited in inflamed bladders (11.8+2.5, n=4, p<0.014). These changes were partly mediated by substance P as 4mg/kg of CP 96,345, a selective NK-1 receptor antagonist, increased fusion in inflamed bladders to 22.2+8.1, n=4, p<0.04), but had no effect on control bladders (25.8+5.5, n=4). Hence, the inflammatory response of the urinary bladder includes vacuolation of the subapicat compartment of transitional epithelial cells, partly mediated by substance-P dependent inhibition of endosomal fusion.

Duke Scholars

Author Timothy Grant Hammond Medicine, Nephrology