Characteristics of spontaneous calcium oscillations in renal tubular epithelial cells.

BACKGROUND

The kidney is a major organ involved in calcium (Ca(2+)) metabolism. Ca(2+) is transported through renal tubular epithelial cells. The intracellular free calcium concentration (Ca(2+)) is tightly controlled at a low concentration, but transient increases and oscillations in Ca(2+) are induced by various conditions. In this study, we investigated the mechanisms underlying the spontaneous Ca(2+) oscillations observed in MDCK cells.

METHODS

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

RESULTS

Spontaneous Ca(2+) oscillations occurred in MDCK cells. The oscillations occurred irregularly and were not transmitted to neighboring cells. Spontaneous Ca(2+) oscillations in MDCK cells were initiated by Ca(2+) release from ryanodine/IP(3)-sensitive intracellular calcium stores, and their frequency was largely unaffected by the extracellular Ca(2+) 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 Ca(2+) release from ryanodine/IP(3)-sensitive intracellular calcium stores mediates spontaneous Ca(2+) oscillations in MDCK cells. Calcium oscillations may be associated with the function of the renal tubular epithelial cells.