Characteristics of spontaneous calcium oscillations in renal tubular epithelial cells

Background

The kidney is a major organ involved in calcium (Ca²⁺) metabolism. Ca²⁺ is transported through renal tubular epithelial cells. The intracellular free calcium concentration (Ca²⁺]_i) is tightly controlled at a low concentration, but transient increases and oscillations in Ca²⁺]_i are induced by various conditions. In this study, we investigated the mechanisms underlying the spontaneous Ca²⁺]_i oscillations observed in MDCK cells.

Methods

Ca²⁺]_i was monitored in fura-2-loaded Madin-Darby canine kidney (MDCK) cells using a calcium imaging system. We investigated the mechanism by which Ca²⁺]_i changed by applying drugs or by changing the extracellular Ca²⁺ concentration.

Results

Spontaneous Ca²⁺]_i oscillations occurred in MDCK cells. The oscillations occurred irregularly and were not transmitted to neighboring cells. Spontaneous Ca²⁺]_i oscillations in MDCK cells were initiated by Ca²⁺ release from ryanodine/IP₃-sensitive intracellular calcium stores, and their frequency was largely unaffected by the extracellular Ca²⁺ concentration. Moreover, the frequency of the oscillations was increased by extracellular nucleotide, but was decreased when the nucleotides were removed.

Conclusions

Our study suggested that Ca²⁺]_i release from ryanodine/IP₃-sensitive intracellular calcium stores mediates spontaneous Ca²⁺]_i oscillations in MDCK cells. Calcium oscillations may be associated with the function of the renal tubular epithelial cells.