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 beta-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 (QO(2)) and proximal tubule Na+,KC-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 mu M) The present data suggest that amphiphile accumulation may have a potential pathophysiologic role in the proximal tubule during renal ischemia.