EXPRESSION OF SYNTAXINS IN RAT-KIDNEY

Previously, we demonstrated that a putative vesicle-targeting protein, syntaxin-4, is expressed in renal collecting duct principal cells and is localized to the apical plasma membrane, suggesting a role in targ eting aquaporin-2-containing vesicles to the apical plasma membrane. T o investigate whether other syntaxin isoforms are present in the renal collecting duct, we determined the intrarenal localization of syntaxi n-2 and -3. Reverse transcription-polymerase chain reaction (RT-PCR) e xperiments using total RNA extracted from kidney and various organs re vealed that both syntaxin-2 and -3 are expressed in kidney cortex and medulla. RT-PCR experiments using microdissected tubules and vascular structures from the kidney revealed that syntaxin-3 mRNA, but not synt axin-2, is expressed in collecting duct cells. Syntaxin-3 mRNA aias al so relatively abundant in the thick ascending limb of Henle's loop and in vasa recta. Syntaxin-2 mRNA was found chiefly in glomeruli. To inv estigate the localization of syntaxin-3 protein, a peptide-derived pol yclonal antibody was raised in rabbits. In immunoblotting experiments, this antibody labeled a 37-kDa protein in inner medulla that was most abundant in plasma membrane-enriched subcellular fractions. Immunoper oxidase labeling of thin cryosections combined with immunogold electro n microscopy showed that, in contrast to the labeling seen for syntaxi n-4, syntaxin-3 labeling in medullary collecting duct was predominantl y in the basolateral plasma membrane of intercalated cells. These resu lts suggest the possibility that syntaxin-3 may be involved in selecti ve targeting of acid-base transporters and/or in basolateral membrane remodeling in response to systemic acid-bass perturbations.