Substrate oxidation by isolated single nephron segments of the rat

Abstract

Substrate oxidation was assessed by measuring 14CO2 production from 14C-labeled substrates in proximal convoluted tubules (PCT), medullary (MTAL), and cortical (CTAL) thick ascending limb of Henle, nephron segments rich in mitochondria and characterized by active solute transport. PCT, MTAL, and CTAL were dissected from the outer cortex, outer medulla, and the medullary rays of the cortex, respectively, of collagenase-treated rat kidney slices. Tubules were incubated at 37 degrees C in 150 microliters of Krebs-Ringer-bicarbonate buffer (pH, 7.4) with 14C-labeled substrate. 14CO2 production was linear up to 4 and 2 hours in PCT and MTAL, respectively. Freeze-thawing of the tubules markedly decreased 14CO2 production, and the addition of cyanide completely abolished it. The PCT demonstrated marked 14CO2 production from labeled succinate, 2-oxoglutarate, glutamate, glutamine, and malate (approximately 10 to 45 pmoles/mm/hr) and moderate 14CO/ production from citrate (approximately 3 pmoles/ml/hr). Little 14CO2 was released from labeled glucose and lactate in PCT. These results are consistent with the existence of gluconeogenesis in this nephron segment. By contrast, MTAL and CTAL oxidized glucose, 2-oxoglutarate, lactate, glutamate, and glutamine, but not malate, succinate, and citrate. The pentose shunt pathway accounted for approximately half of the 14CO2 produced from 1-14C glucose in MTAL and CTAL. Palmitate oxidation occurred in MTAL and CTAL but minimally in PCT. The results demonstrate a distinct pattern of substrate oxidation in PCT, MTAL, and CTAL where oxidative metabolism is critical to support active solute transport.

Structure-function correlations in erythropoietin formation and oxygen sensing in the kidney

“…The transport work, and hence the energy consumption, of the proximal tubule is quite constant under physiological conditions, and it relies almost completely on oxygen metabolism for energy production [11,25].…”

Illuminating Mitochondrial Function and Dysfunction using Multiphoton Technology

“…Elements of this pathway also regulate the Cl Ϫ and volume sensitivity of all functional members of the cation-chloride co-transporter gene family, including NCC, the two Na ϩ -K ϩ -2Cl Ϫ co-transporters (NKCC1 and NKCC2), and the four K ϩ -Cl Ϫ co-transporters (KCC1 through 4). 3,4 More recently, there are outlines of the interactions of this pathway with aldosterone 8 and angiotensin-dependent 9 regulation of NCC. Variation in the human…”

“…5 In contrast, DT segments, including the TAL, have well-developed glycolytic pathways. 3,4,6,7 Glycolysis occurs in the S3 segment of the proximal tubule, albeit to a lesser extent than in distal tubules, and contributes to maintaining ATP there when mitochondrial function is impaired. 3,8 Mitochondrial ATP production depends on substrate-supported, electron transport-mediated proton extrusion from the mitochondrial matrix that generates a proton gradient across the inner mitochondrial membrane.…”

“…They compose 33% of the volume of proximal convoluted tubular S1 cells, 39% of the cells in the S2 segment, and 22% of the volume of cells in the proximal straight S3 segment; in the medullary and cortical TAL cells, mitochondria account for 30 to 44% of cell volume. 2 Differential tubular cell metabolism is also notable for the absence of aerobic and anaerobic glycolysis in the proximal convoluted tubule (S1), 3,4 which removes an important mechanism for preserving cell ATP and viability during injury. 5 In contrast, DT segments, including the TAL, have well-developed glycolytic pathways.…”

“…A gain-in-function of NCC occurs in pseudohypoaldosteronism type II (PHA-II; also known as Gordon syndrome or hereditary hypertension with hyperkalemia); however, this disorder is caused by mutations not in NCC but in two of the four WNK (with no K/lysine) kinases, so-named for the absence of a conserved catalytic lysine. 3,4 Since the seminal genetic study implicating WNK1 and WNK4 in PHA-II, 5 an increasingly populous signaling complex has been uncovered, encompassing WNK1, WNK3, WNK4 and the downstream STE20/SPS1-related proline/alanine-rich kinase (SPAK) and oxidative stress-responsive kinase 1 (OSR1). 3,4 WNK1, 5 WNK3, 6 WNK4, 5 and SPAK 7 all are coexpressed with NCC in the DCT.…”