Calbindin-D28K facilitates cytosolic calcium diffusion without interfering with calcium signaling

Area of Science:

• Nephrology
• Cell Physiology
• Calcium Homeostasis

Background:

• Calbindin-D28K is a calcium-binding protein implicated in calcium transport.
• Its precise role in the kidney's calcium handling and signaling pathways remains incompletely understood.
• The cortical collecting system is a key site for regulating calcium reabsorption.

Purpose of the Study:

• To investigate the role of calbindin-D28K in transcellular calcium transport.
• To examine the influence of calbindin-D28K on intracellular calcium signaling in the rabbit cortical collecting system.
• To determine the effect of 1,25(OH)2D3 on calbindin-D28K expression and function.

Main Methods:

• Isolation and culture of rabbit kidney connecting tubules and cortical collecting ducts.
• Immunodissection to isolate principal and intercalated cells.
• Measurement of cellular calbindin-D28K levels, transcellular calcium transport, and intracellular calcium ([Ca2+]i) dynamics.

Main Results:

• Calbindin-D28K was localized to principal cells in the cortical collecting system.
• 1,25(OH)2D3 significantly increased calbindin-D28K levels and stimulated transcellular calcium transport.
• Calcium chelator BAPTA mimicked the stimulatory effect on calcium transport but altered intracellular calcium oscillations, unlike calbindin-D28K.

Conclusions:

• Calbindin-D28K plays a role in enhancing transcellular calcium transport in the rabbit cortical collecting system.
• Calbindin-D28K's slow calcium-binding kinetics prevent it from modulating intracellular calcium oscillations.
• The presence of calcium chelators, not necessarily calbindin-D28K levels, is sufficient to enhance transcellular calcium transport.