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Polycations induce calcium signaling in glomerular podocytes.
F Rüdiger1, R Greger, R Nitschke
1Division of Nephrology, Department of Medicine, University of Freiburg, Germany.
Kidney International
|November 26, 1999
Summary
Polycations like protamine sulfate increase cytosolic calcium activity ([Ca2+]i) in podocytes. This rise in [Ca2+]i may be an early step in foot process retraction and proteinuria.
Area of Science:
- Nephrology
- Cell Biology
- Molecular Physiology
Background:
- Podocyte foot process retraction and proteinuria are induced by polycation perfusion.
- The polyanionic nature of the podocyte surface is implicated in this process.
Purpose of the Study:
- To investigate the impact of protamine sulfate and various dextrans (anionic, neutral, cationic) on podocyte cytosolic calcium activity ([Ca2+]i).
Main Methods:
- Cytosolic calcium activity ([Ca2+]i) was measured in cultured mouse podocytes using the fura-2/AM fluorescence dye.
- Experiments involved varying concentrations of polycations and testing inhibitors.
Main Results:
- Protamine sulfate and DEAE-dextran (cationic) caused a concentration-dependent increase in [Ca2+]i.
- Heparin inhibited protamine sulfate's effect, while extracellular calcium reduction partially reduced the [Ca2+]i response to both polycations.
- Ion channel inhibitors did not affect the calcium increase, but thapsigargin revealed endoplasmic reticulum involvement.
Conclusions:
- Polycations significantly elevate podocyte cytosolic calcium ([Ca2+]i).
- This increase in [Ca2+]i is a potential early mechanism driving protamine sulfate-induced podocyte foot process retraction.