The effects of short-term
anoxia and
hypoxia were studied in a rabbit proximal renal tubule
suspension in order to avoid the hemodynamic consequences of clamp-induced
ischemia. The
suspension was subjected to
anoxia for 10-40 min and the effects on a number of cellular transport and respiratory parameters were monitored. Cellular respiration was measured upon addition of
nystatin (Nys) to maximally stimulate Na pump activity. Mitochondrial respiration was measured in the tubules by addition of
digitonin and
ADP to obtain the state 3 respiratory rate. The release of
lactate dehydrogenase (LDH) was measured as an index of plasma membrane damage. The cellular contents of K and Ca were also measured. Results show that 10 and 20 min of
anoxia partially inhibited Nys-stimulated and mitochondrial respiration, and partially decreased the K contents, but all these effects were largely reversible after 20 min of reoxygenation. After 40 min of
anoxia and 20 min of reoxygenation, all these variables remained irreversibly inhibited: Nys-stimulated respiration by 54%, mitochondrial respiration by 50%, K content by 42%, and LDH release was 40% of total. Ca content decreased slightly during
anoxia, but increased up to fourfold during severe
hypoxia; the excess Ca was released during the first 10 min of reoxygenation. The degree of respiratory impairment was identical during
anoxia or
hypoxia, suggesting that Ca accumulation was not associated with the impairment. Decreasing the extracellular Ca to 2.5 microM decreased LDH release significantly during
anoxia, suggesting that plasma membrane damage during
anoxia may be associated with increased intracellular free Ca. Addition of Mg-
adenosine triphosphate during
anoxia dramatically improved recovery of all the measured parameters after the anoxic period.