Physiological pH. Effects on posthypoxic proximal tubular injury

Area of Science:

• Renal physiology and pathophysiology
• Cellular injury mechanisms
• Hypoxia-reoxygenation injury

Background:

• Tissue acidosis self-corrects rapidly after oxygen (O2) deprivation.
• The impact of this pH correction on posthypoxic proximal tubular injury is not fully understood.
• Exploring protective strategies against this injury is crucial.

Purpose of the Study:

• To assess the effect of pH correction on the induction and pathways of posthypoxic proximal tubular injury.
• To explore methods for preventing this resultant injury.

Main Methods:

• Isolated rat proximal tubular segments (PTSs) underwent hypoxia/reoxygenation.
• Experiments varied incubation pH (7.4 vs. 6.8) and reoxygenation conditions (constant pH vs. pH correction).
• Lactate dehydrogenase (LDH) release, ATP depletion, lipid peroxidation, and membrane deacylation were measured.

Main Results:

• Acidosis (pH 6.8) significantly blocked hypoxic LDH release compared to pH 7.4.
• Correcting pH post-hypoxia (realkalinization) caused immediate and marked cell death, independent of lipid peroxidation or new deacylation.
• This realkalinization injury was preventable by glycine addition, transient hypothermia, or a delayed reoxygenation period.

Conclusions:

• Posthypoxic 'pH shock' from rapid realkalinization causes cell death by removing acidosis's protective effect, not by de novo injury.
• The injury is preceded by a depressed ATP/ADP ratio, suggesting impaired cell energetics.
• Effective prevention strategies exist, indicating potential for salvaging severely damaged posthypoxic proximal tubules.