Cytosolic free calcium levels in rabbit proximal kidney tubules.

Cytosolic free Ca levels were measured in isolated rabbit proximal kidney tubules using a previously described null-point method (19). Control values for cytosolic free Ca levels averaged 0.45 +/- 0.09 microM (n = 13). Addition of 1 microM A23187, an agent expected to increase ionized Ca levels, resulted in an eightfold increase in the null point. Total mitochondrial Ca content was determined by measuring the fluorocyanocarbonylphenylhydrazine-releasable Ca. 80% of the total cell Ca was found to be mitochondrial. These results suggest that the mitochondria play an important role in the regulation of cytosolic free Ca levels in mammalian proximal kidney tubules.