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Functional evidence for a Ca2+/polyvalent cation sensor in the mouse thick ascending limb
M Paulais1, M Baudouin-Legros, J Teulon
1Institut National de la Santé et de la Recherche Médicale Unité 323, Faculté de Médecine Necker, Paris, France.
The American Journal of Physiology
|November 1, 1996
Summary
Extracellular polyvalent cations like calcium, gadolinium, and neomycin activate a calcium sensor in mouse kidney tubules, primarily the thick ascending limb, influencing cytosolic calcium levels.
Area of Science:
- Nephrology
- Cell Physiology
- Molecular Biology
Background:
- Cytosolic free Ca2+ concentration ([Ca2+]i) is critical for kidney tubule function.
- The role of extracellular polyvalent cations in regulating [Ca2+]i in nephron segments is not fully understood.
Purpose of the Study:
- To investigate the effects of extracellular polyvalent cations on [Ca2+]i in isolated mouse nephron segments.
- To identify the specific segments involved and the mechanisms of cation-induced calcium signaling.
Main Methods:
- Isolated mouse nephron segments were used.
- Fura 2 microfluorometry was employed to measure [Ca2+]i.
- Various extracellular cations (Ca2+, Gd3+, Neo, Ba2+, Mg2+, Mn2+) and inhibitors (thapsigargin, La3+, nifedipine) were applied.
Main Results:
- Extracellular Ca2+, Gd3+, and Neo increased [Ca2+]i in cortical thick ascending limb (CTAL) tubules.
- These cations mobilized internal Ca2+ stores, as evidenced by thapsigargin sensitivity.
- Similar, though less pronounced, effects were observed in other segments like MTAL and collecting ducts, but not in the descending thin limb.
Conclusions:
- A Ca2+-mobilizing polyvalent cation sensor, similar to that in parathyroid cells, is present in mouse nephron segments.
- This sensor is predominantly located in the CTAL, with functional presence in MTAL and distal segments.
- The findings suggest a novel mechanism for cation sensing and calcium regulation within the kidney.