Increases of cell ATP produced by exogenous adenine nucleotides in isolated rabbit kidney tubules

Abstract

The effects of exogenous nucleotides on adenine nucleotide metabolism and cell cation levels in normal and O2-deprived isolated rabbit kidney tubules were studied to gain insight into ways in which exogenous nucleotides could contribute to ameliorating O2 deprivation-induced injury. In control oxygenated tubules, 250 microM exogenous ATP, ADP, or AMP resulted in two- to threefold increases of cell ATP over 75-90 min of incubation and smaller relative increases of ADP and AMP. GTP was not increased. Exogenous adenosine, inosine, and hypoxanthine were substantially less effective at increasing intracellular nucleotides than equimolar concentrations of exogenous nucleotides. Nucleotide-treated cells had higher levels of Ca2+ and Mg2+ than untreated cells. Treatment of O2-deprived tubules with exogenous Mg-ATP improved recovery of ATP levels following O2 deprivation, and tubules with mild injury increased their ATP levels to supranormal values such as those seen in control oxygenated tubules treated with nucleotides. Increases of tubule cell ATP levels required ongoing oxidative metabolism and thus were not evident until the reoxygenation recovery period. Exogenous ATP produced some improvement of other injury-associated metabolic parameters but did not substantially alter the overall pattern of tubule susceptibility to lethal cell injury. Allopurinol did not affect the behavior of oxygenated or O2-deprived tubules irrespective of the presence of exogenous ATP. These data clarify the potential for manipulating intracellular ATP levels with exogenous nucleotides and the functional consequences of such manipulation in oxygenated and O2-deprived renal tubule cells.