Metabolic effects of 4-pentenoate on isolated dog kidney tubules

The effects of 4-pentenoate (0.01 to 10 mM) were studied on suspensions of cortical tubules and of thick ascending limbs (TAL) prepared from dog kidneys. When cortical tubules were incubated with 1 mM glutamine, 4-pentenoate accelerated glutamine uptake, ammoniagenesis, and the production of alpha-ketoglutarate, lactate and pyruvate, but decreased gluconeogenesis. With 5 mM glutamine, the marked accumulation of alpha-ketoglutarate reversed the net fluxes through the alanine and aspartate aminotransferases. When cortical tubules or TAL were incubated with lactate, its utilization and gluconeogenesis (in cortical tubules) were markedly decreased by 4-pentenoate. The mitochondrial NAD+/NADH ratio was markedly increased by 4-pentenoate in cortical tubules but not in TAL. The production of 14CO2 from 14C[1]-pyruvate or 14C-[1]-alpha-ketoglutarate was decreased by approximately 60% by 4-pentenoate in cortical tubules but not in TAL. In cortical tubules, these findings are best explained by depletion of mitochondrial free CoA, inhibition of pyruvate and alpha-ketoglutarate dehydrogenases and decreased mitochondrial NADH. By contrast, in TAL, accumulation of reducing equivalents probably resulted from the metabolism of 4-pentenoate itself.