NMR studies of the effect of Mg2+ on post-ischemic recovery of ATP and intracellular sodium in perfused kidney

Phosphatidylinositol 3-kinase-mediated effects of glucose on vacuolar H+-ATPase assembly, translocation, and acidification of intracellular compartments in renal epithelial cells

Vacuolar H+-ATPases (V-ATPases) are a family of ATP-driven proton pumps. They maintain pH gradients between intracellular compartments and are required for proton secretion out of the cytoplasm. Mechanisms of extrinsic control of V-ATPase are poorly understood. Previous studies showed that glucose is an important regulator of V-ATPase assembly in Saccharomyces cerevisiae. Human V-ATPase directly interacts with aldolase, providing a coupling mechanism for glucose metabolism and V-ATPase function. Here we show that glucose is a crucial regulator of V-ATPase in renal epithelial cells and that the effect of glucose is mediated by phosphatidylinositol 3-kinase (PI3K). Glucose stimulates V-ATPase-dependent acidification of the intracellular compartments in human proximal tubular cells HK-2 and porcine renal epithelial cells LLC-PK1. Glucose induces rapid ATP-independent assembly of the V1 and Vo domains of V-ATPase and extensive translocation of the V-ATPase V1 and Vo domains between different membrane pools and between membranes and the cytoplasm. In HK-2 cells, glucose stimulates polarized translocation of V-ATPase to the apical plasma membrane. The effects of glucose on V-ATPase trafficking and assembly can be abolished by pretreatment with the PI3K inhibitor LY294002 and can be reproduced in glucose-deprived cells by adenoviral expression of the constitutively active catalytic subunit p110alpha of PI3K. Taken together these data provide evidence that, in renal epithelial cells, glucose plays an important role in the control of V-ATPase-dependent acidification of intracellular compartments and V-ATPase assembly and trafficking and that the effects of glucose are mediated by PI3K-dependent signaling.

Nuclear magnetic resonance spectroscopy and imaging in animal research

Nuclear magnetic resonance (NMR) spectroscopy and imaging can be used to investigate, noninvasively, a wide range of biological processes in systems as diverse as protein solutions, single cells, isolated perfused organs, and tissues in vivo. It is also possible to combine different NMR techniques enabling metabolic, anatomical, and physiological information to be obtained in the same experiment. This review provides a simple overview of the basic principles of NMR and outlines both the advantages and disadvantages of NMR spectroscopy and imaging. A few examples of potential applications of NMR spectroscopy and imaging are presented, which demonstrate the range of questions that can be asked using these techniques. The potential impact of using NMR techniques in a biomedical research program on the total number of animals required for specific investigations, as well as the number of animals used in research, are discussed. The article concludes with a personal perspective on the impact of continuing improvements in NMR technology for future applications in animal research.

Normothermic blood perfusion of isolated rabbit kidneys. II. In vitro evaluation of renal function followed by orthotopic transplantation

This study describes the use of a blood perfusion apparatus to assess the renal function of isolated kidneys. Eight fresh kidneys were obtained from healthy rabbits and perfused with blood at 36 degrees C for 2 hours. Rabbit blood was drawn and diluted to a hematocrit of 25%. The kidneys were evaluated for their capacity to support life in an autograft model. Blood and urine samples were taken at regular time intervals during kidney perfusion. Serum creatinine was measured in surviving rabbits after transplantation. Over the course of the perfusion, arterial pressure was maintained at 87.2 +/- 5.5 mm Hg. The renal blood flow (3.7 +/- 1.0 ml/min per g) and urine output (0.11 +/- 0.04 ml/min per g) were continuously monitored. Glomerular filtration rate (0.29 +/- 0.02 ml/min per g) and fractional reabsorption (FR) of sodium and glucose indicated appreciable tubular function (FR(Na) = 67.9 +/- 8.5%, FR(Glu) = 91.2 +/- 5.8%). Protein was excluded from urine at 99.8% +/- 0.1%. After transplantation, the peak creatinine was 6.8 +/- 3.2 mg/dl at 1.90 +/- 0.92 days for the seven surviving rabbits and was above 16 mg/dl for the only rabbit that died 4 days after operation. The level of free hemoglobin generated at the end of the perfusion (2.6% +/- 2.8%) was correlated with the postoperative peak creatinine (r2 = 0.84). Perfusion of seven additional kidneys by using the roller pump lead to a final hemolysis of only 0.34 +/- 0.14%. Kidneys transplanted after 2 hours of blood perfusion were able to resume normal function and support life. Hemolysis was a measurable stress factor causing delayed function of the kidney after transplantation. Introduction of a roller pump significantly reduced the hemolysis.

Reconstitution of ATP-dependent movement of endocytic vesicles along microtubules in vitro: an oscillatory bidirectional process

We have previously used the asialoglycoprotein receptor system to elucidate the pathway of hepatocytic processing of ligands such as asialoorosomucoid (ASOR). These studies suggested that endocytic vesicles bind to and travel along microtubules under the control of molecular motors such as cytoplasmic dynein. We now report reconstitution of this process in vitro with the use of a microscope assay to observe the interaction of early endocytic vesicles containing fluorescent ASOR with fluorescent microtubules. We find that ASOR-containing endosomes bind to microtubules and translocate along them in the presence of ATP. This represents the first time that mammalian endosomes containing a well-characterized ligand have been directly observed to translocate on microtubules in vitro. The endosome movement does not require cytosol or exogenous motor protein, is oscillatory, and is directed toward the plus and minus ends at equal frequencies. We also observe endosomes being stretched in opposite directions along microtubules, suggesting that microtubules could provide a mechanical basis for endocytic sorting events. The movement of endosomes in vitro is consistent with the hypothesis that microtubules actively participate in the sorting and distribution of endocytic contents.

Sodium TQF NMR and intracellular sodium in isolated crystalloid perfused rat heart

The feasibility of monitoring intracellular sodium changes using Na triple quantum filtered NMR without a chemical shift reagent (SR) was investigated in an isolated rat heart during a variety of interventions for Na(i) loading. Perfusion with 1 mM ouabain or without K+ present in the perfusate for 30 min produced a rise of the Na TQF signal with a plateau of approximately 190% and approximately 228% relative to the preintervention level, respectively. Stop-flow ischemia for 30 min resulted in a TQF signal growth of approximately 147%. The maximal Na TQF signal increase of 460% was achieved by perfusion without K+/Ca2+, corresponding to an elimination of the Na transmembrane gradient. The observed values of Na NMR TQF growth in the physiological and pathological ranges are in agreement with reported data by other methods and have a linear correlation with intracellular sodium content as determined in this study by Co-EDTA method and by sucrose-histidine washout of the extracellular space. Our data indicate that the increase in Na TQF NMR signal is determined by the growth of Na(i), and the extracellular Na contribution to the total TQF signal is unchanged at approximately 64%. In conclusion, Na TQF NMR without using SR offers a unique and noninvasive opportunity to monitor alterations of intracellular sodium. It may provide valuable insights for developing cardioprotective strategies and for observing the effects of pharmaceutical treatments on sodium homeostasis.

Evaluation of multiple-quantum-filtered 23Na NMR in monitoring intracellular Na content in the isolated perfused rat heart in the absence of a chemical-shift reagent

The feasibility of employing triple-quantum-filtered (TQF) or double-quantum-filtered (DQF) 23Na NMR spectra to monitor intracellular Na (Nain) content in isolated rat hearts perfused in the absence of a chemical-shift reagent (SR) was investigated. This necessitated characterization of the following: first, the pool of Nain represented by the intracellular TQF (TQFin) spectrum; second, the maximum extent to which altered transverse relaxation times affect TQFin spectral amplitudes; and finally, the situations for which the SR-free method can reliably be applied. The rates of increase in peak amplitudes of both intracellular TQF spectra, adjusted for changes in both fast (T2f) and slow (T2s) transverse relaxation times, and intracellular single-quantum (SQin) spectra were identical during no-flow ischemia, indicating that TQFin and SQin spectra represent the same Nain population. Addition of an Na/K ATPase inhibitor, ouabain (>/=500 microM), and no-flow ischemia induced similar rates of increase of Nain content. However, the Nain level for which the T2 values started to increase was lower for ischemic (<140% of preischemic values) than for ouabain-exposed (>165%) hearts, which is consistent with the known earlier onset of intracellular swelling in ischemic hearts. Exposure of hearts to hyperosmotic perfusate (200 mM sucrose) increased [Nain], due to a decreased cell volume and an unchanged Nain content, but caused a decrease in T2 values, a trend opposite to that observed with exposure of hearts to ouabain or ischemia. T2 values therefore consistently correlated only with cell volume, not with Nain content or concentration, indicating an important role for intracellular macromolecule concentration in modulating transverse relaxation behavior. The combined effect of ischemia-induced increases in T2 values and their inhomogeneous broadened forms was an approximately 6% overestimation of Nain content from amplitudes of SR-aided TQFin spectra, indicating negligible effect of transverse relaxation-dependent alterations on TQFin spectral amplitudes. Thus, Nain content may be reliably determined from SR-free TQF spectra when the contribution from extracellular Na does not appreciably vary, such as during constant pressure perfusion. Following complete reduction in perfusion pressure, both SR-free TQF and DQF spectra respond to increases in Nain content. However, SR-free DQF NMR provides an estimate of Nain content much closer to that provided by the SR-aided method, due to the appreciable decrease of the extracellular DQF signal resulting from destructive interference between second- and third-rank tensors.