Calcium Compartmentation in Isolated Renal Tubules in Suspension

Recent developments in the use of fluorescent Ca2+ indicators and the electron microprobe have provided major insights into the regulation of cell Ca2+ metabolism (l-3). However, fluorescent dyes are not optimally applicable to all cell types under all study conditions, particularly those involving cell injury, and electron probe microanalysis is complex and requires specialized facilities. Several consistent changes of total cell Ca2+ have been identified during studies of the response of suspensions of isolated renal proximal tubules to oxygen deprivation-induced injury. In particular, tubule cell Ca ” increases during hypoxic oxygen deprivation and then decreases with reoxygenation (4-6). Tubule cell Ca2+ also increases when tubules are treated with exogenous ATP and then declines (5). Increases of total cell Ca2 ’ of the magnitude observed must reflect sequestered Ca2+ (7), a conclusion supported by the fact that the increases of cell Ca2+ do not occur under conditions of complete anoxia (6). Because of the proclivity of mitochondria to continue sequestering Ca2 ’ for long periods after cell disruption and their enormous capacity (7-IO), the question remains whether the changes of tota