Hypoxia-induced amphiphiles inhibit renal Na⁺,K⁺-ATPase

We have characterized the effects of hypoxia on carnitine metabolism in proximal tubules. Hypoxia for 10 minutes resulted in a significant increase in the mass of long chain acylcarnitines (LCAC) (control 53 ± 20 vs. hypoxia 118 ± 38 pmol·mg^-1 protein). Since LCAC are proximal metabolites in the β-oxidation of fatty acids, these data suggest that inhibition of fatty acid oxidation occurs during hypoxia in the proximal tubule. In addition to LCAC accumulation, hypoxia resulted in a significant increase in the mass of lysoplasmenylcholine LPLasCho (control 62 ± 15 pmol/mg vs. 20 min hypoxia 146 ± 21 pmol/mg protein, N = 4) and also in increases in the mass of monoacyl LPC (control 122 ± 24 pmol/mg protein vs. 283 ± 35 pmol/mg protein after 40 min of hypoxia). We tested the possibility that these compounds that accumulate during hypoxia could inhibit proximal tubule Na⁺,K⁺-ATPase. LPC, LPlasC, and LCAC inhibited proximal tubule nystatin-stimulated oxygen consumption (QO₂) and proximal tubule Na⁺,K⁺-ATPase activity in a dose-dependent manner. In addition, LPC, LPlasC, and LCAC directly inhibited (65%, 80%, and 60%, respectively) Na⁺,K⁺-ATPase activity purified from kidney cortex at similar concentrations at which they accumulate during hypoxia (above 25 μM). The present data suggest that amphiphile accumulation may have a potential pathophysiologic role in the proximal tubule during renal ischemia.