The opossum kidney cell type IIa Na/P(i) cotransporter is a phosphoprotein
M Jankowski1, H Hilfiker, J Biber
1Institute of Physiology, University of Zurich, Zurich, Switzerland.
Kidney & Blood Pressure Research
|February 15, 2001
Summary
Parathyroid hormone (PTH) reduces phosphate reabsorption by affecting the type IIa Na/P(i) cotransporter. This study found that while the transporter is phosphorylated, changes in its phosphorylation do not directly cause PTH-induced inhibition of phosphate transport.
Area of Science:
- Nephrology
- Molecular Biology
- Cell Physiology
Background:
- Parathyroid hormone (PTH) inhibits proximal tubular phosphate (P(i)) reabsorption.
- This inhibition is linked to reduced type IIa Na/P(i) cotransporter expression at the cell membrane.
- The role of cotransporter phosphorylation in this process was unclear.
Purpose of the Study:
- To investigate the phosphorylation status of the type IIa Na/P(i) cotransporter.
- To determine if changes in phosphorylation mediate PTH-induced inhibition of P(i) transport.
Main Methods:
- Utilized opossum kidney cells as a proximal tubule model.
- Assessed cotransporter phosphorylation via immunoprecipitation and autoradiography.
- Evaluated transporter expression using Western blotting and transport activity through P(i) uptake assays.
Main Results:
- The type IIa Na/P(i) cotransporter is phosphorylated under basal conditions.
- PTH treatment led to decreased cotransporter phosphorylation.
- A protein phosphatase inhibitor did not prevent PTH-induced transport inhibition but reduced transporter degradation.
Conclusions:
- The type IIa Na/P(i) cotransporter is a phosphoprotein.
- Alterations in the phosphorylation of this transporter do not appear to be the primary mechanism for PTH-induced P(i) transport inhibition.
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