The purpose of the present study was to determine the effect of protein kinase A and protein kinase C activation on the membrane expression of NaPi- 4, the type II sodium-phosphate cotransporter in OK cells. NaPi-4 expression was measured using polyclonal antisera produced in rabbits against a peptide identical to the carboxy-terminal 12-amino acid sequence of NaPi-4. The antisera identified an apically localized protein by confocal imaging of intact OK cells and a broad band of 110-140 kDa by immunoblot analysis of OK cell membranes. Treatment of OK cells with parathyroid hormone (PTH) decreased the intensity of the 110- to 140-kDa band, which was detectable by 2 h, maximal by 4 h at 62%, and sustained for 24 h. 8-Bromo-cAMP (8-BrcAMP) inhibited NaPi-4 expression for up to 24 h by over 90%. However, phorbol 12- myristate 13-acetate inhibited NaPi-4 expression by less than 10%. PTH-(3- 34), a fragment which stimulates only protein kinase C, inhibited phosphate transport but also had no effect on NaPi-4 expression. We conclude that protein kinase A but not protein kinase C inhibits sodium-phosphate uptake in OK cells by downregulation of NaPi-4 expression.
- 8- bromoadenosine 3',5'-cyclic monophosphate
- Confocal imaging
- Opossum kidney cells
- Parathyroid hormone
- Phorbol 12-myristate 13-acetate
- Type II sodium-phosphate cotransporter
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