Mechanisms whereby exogenous adenine nucleotides improve rabbit renal proximal function during and after anoxia

Abstract

When a suspension of rabbit proximal tubules is subjected to anoxia, ATP falls by 80-90% during 40 min of anoxia, and upon reoxygenation (reox) the cells only recover 25-50% of their initial ATP. Addition of Mg-ATP (magnesium chloride-treated ATP), Mg-ADP, or Mg-AMP (five aliquots of 200 nmol/ml added 10 min apart) during anoxia causes complete recovery of ATP levels, and respiratory and transport function after 40 min of reox. Similar additions of adenosine (ADO), or inosine (INO), or Mg-ATP only during reox are less effective. Lactate dehydrogenase (LDH) release after 40 min of anoxia is 30-40% under control conditions, only 10-15% when adenine nucleotides or ADO are added during anoxia, and 20% when INO is added, suggesting that these additions may stabilize the plasma membrane during anoxia and help preserve cellular integrity. During reox, recovery may depend on the entry of ATP precursors and, therefore, we explored the mechanism whereby exogenous ATP increases the intracellular ATP content. Additions of Mg-ATP, Mg-ADP, or Mg-AMP to continuously oxygenated tubules increase cellular ATP content three- to fourfold in 1 h. The added ATP and ADP are rapidly degraded to AMP, and more slowly to ADO, INO, and hypoxanthine. Furthermore, the ATP-induced increase in cellular ATP is abolished by the exogenous addition of adenosine deaminase, which converts extracellular ADO to INO. These results suggest that the increase in cellular ATP requires extracellular ADO. The ADO obtained from the breakdown of AMP may be preferentially transported into the renal cells to be resynthesized into cellular AMP and ATP.