O2 affinity of cross-linked hemoglobins modifies O2 metabolism in proximal tubules

Previous experiments using cross-linked tetrameric hemoglobins ( XLHb) to perfuse isolated rat kidneys showed that high-O-2-affinity XLHb improved proximal tubule function more effectively than low-O-2-affinity XLHb. To determine how function was improved, proximal tubule fragments were incubated with albumin, Hb(34) [half-saturation point (P-50) 34 Torr], or Hb(13) (P-50 13 Torr) with PO2 values ranging from 22 to 147 Torr. ATP content reflected O-2 delivery to mitochondria. Both XLHb increased ATP, Hb(34) with PO2 greater than or equal to 47 Torr and Hb(13) with PO2 less than or equal to 47 Torr. XLHb increased Na-K-ATPase activity (Rb-86 uptake) in similar PO2-dependent patterns. O-2 consumption ((Q)over dot O-2) was measured in a closed, well-stirred chamber. Ouabain- and oligomycin-inhibited (Q) over dot O-2, reflecting Na-K-ATPase activity and oxidative phosphorylation, respectively, mirrored the PO2-dependent patterns of ATP and 86Rb uptake. As PO2 fell below the midpoint of XLHb desaturation, (Q) over dot O-2, uncoupled from oxidative phosphorylation, transiently increased. The increase was most pronounced with Hb(34). Nitro-L-arginine methyl ester had no effect on (Q) over dot O-2. Inhibitors of NAD(P) H oxidases and diamine oxidase partially prevented the (Q) over dot O-2 surge with Hb(34). In conclusion, facilitated diffusion accounts for PO2-dependent XLHb effects on ATP content and Na-K-ATPase and for Hb(13)' s effectiveness in hypoxic perfused kidneys. NO scavenging was not a factor. O-2-binding characteristics influence XLHb effects on mitochondria and O-2-sensitive enzymes such as oxidases.