GENTAMICIN INHIBITS RAT RENAL CORTICAL HOMOTYPIC ENDOSOMAL FUSION - ROLE OF MEGALIN

Megalin, a giant glycoprotein receptor heavily concentrated in the ear ly endosomal pathway of renal proximal tubular cells, binds gentamicin with high affinity and delivers the drug to lysosomes. Utilizing an i n vitro reconstitution assay, we tested whether gentamicin-induced vac uolation is associated with inhibition of early endosomal fusion, as w ell as whether megalin plays a role in mediating these effects. Pretre atment of rats with gentamicin inhibited rat renal proximal tubular ho motypic endosomal fusion. Administered simultaneously, gentamicin and polymers of polyaspartic acid, which protect against the hemodynamic e ffects of gentamicin nephrotoxicity, had no net effect on fusion. Poly aspartic acid alone had no effect on fusion. Antisera to the tail of t he megalin/gentamicin receptor inhibited fusion, whereas nonspecific c ontrols had no effect. Peptides matching homologous NPXY repeat sequen ce motifs in the cytosolic tail stimulated endosomal fusion, whereas r everse sequence control peptides had no effect. These data suggest tha t gentamicin inhibition of endosomal fusion in the renal proximal tubu le is a damage mechanism mediated by specific peptide sequences in the cytosolic tail of the giant gentamicin-binding receptor megalin and t hat receptors can effect the fusion properties of membranes in which t hey reside.