title: Rapid downregulation of rat renal Na/P(i) cotransporter in response to parathyroid hormone involves microtubule rearrangement.
abstract: Renal proximal tubule cells express in their apical brush border membrane (BBM) a Na/P(i) cotransporter type IIa that is rapidly downregulated in response to parathyroid hormone (PTH). We used the rat renal Na/P(i) cotransporter type IIa (NaPi-2) as an in vivo model to assess early cellular events in the rapid downregulation of this transporter. When rats were treated with PTH for 15 minutes, NaPi-2 abundance in the BBM was decreased. In parallel, transporter accumulated in intracellular vesicles. Concomitantly, microtubules (MTs) were found to form dense bundles of apical-to-basal orientation. After 60 minutes of PTH action, the cells were vastly depleted of NaPi-2, whereas their microtubular cytoskeleton had returned to its normal appearance. Prevention of MT rearrangement by taxol resulted in accumulation of NaPi-2 in the subapical cell portion after 15 minutes and a strong delay in depletion of intracellular transporter after 60 minutes of PTH action. Furthermore, the subapical accumulation of NaPi-2 was associated with the expansion of dense apical tubules of the subapical endocytic apparatus (SEA). Depolymerization of MTs by colchicine likewise caused a retardation of intracellular NaPi-2 depletion. These results suggest that NaPi-2 is downregulated in response to PTH through a rapid endocytic process in 2 separate steps: (a) internalization of the transporter into the SEA, and (b) its delivery to degradative organelles by a trafficking mechanism whose efficiency depends on a taxol-sensitive rearrangement of MTs.
authors.affiliation: Institute of Anatomy, University of Zürich, CH-8057 Zürich, Switzerland.
authors.forename: M
authors.initials: M
authors.lastname: Lötscher
authors.forename: Y
authors.initials: Y
authors.lastname: Scarpetta
authors.forename: M
authors.initials: M
authors.lastname: Levi
authors.forename: N
authors.initials: N
authors.lastname: Halaihel
authors.forename: H
authors.initials: H
authors.lastname: Wang
authors.forename: H K
authors.initials: HK
authors.lastname: Zajicek
authors.forename: J
authors.initials: J
authors.lastname: Biber
authors.forename: H
authors.initials: H
authors.lastname: Murer
authors.forename: B
authors.initials: B
authors.lastname: Kaissling
mesh_terms: D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D003078:Colchicine / Q000494:pharmacology; D004705:Endocytosis / Q000187:drug effects; D007150:Immunohistochemistry; D007687:Kidney Tubules, Proximal / Q000187:drug effects* / Q000378:metabolism* / Q000648:ultrastructure; D008297:Male; D008854:Microscopy, Electron; D008870:Microtubules / Q000187:drug effects*; D008871:Microvilli / Q000187:drug effects / Q000378:metabolism; D017239:Paclitaxel / Q000494:pharmacology; D010281:Parathyroid Hormone / Q000494:pharmacology*; D010446:Peptide Fragments / Q000494:pharmacology*; D010710:Phosphates / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D012964:Sodium / Q000378:metabolism; D050608:Sodium-Phosphate Cotransporter Proteins; D050613:Sodium-Phosphate Cotransporter Proteins, Type IIa; D027981:Symporters
chemical_list: D002352:Carrier Proteins; D010281:Parathyroid Hormone; D010446:Peptide Fragments; D010710:Phosphates; C493556:Slc34a1 protein, rat; D050608:Sodium-Phosphate Cotransporter Proteins; D050613:Sodium-Phosphate Cotransporter Proteins, Type IIa; D027981:Symporters; D012964:Sodium; D017239:Paclitaxel; D003078:Colchicine