Sodium influxes in renal epithelial LLC-PK1/Cl4 cells monitored by 23Na NMR

Effect of gossypol on cultured TM3 Leydig and TM4 Sertoli cells: 31P and 23Na NMR study

The effects of gossypol on glucose metabolism, ATP levels and intracellular sodium levels in murine TM3 Leydig and TM4 Sertoli cell lines were investigated, and their response compared. Relative ATP levels and sodium ion levels in the two cell lines were determined by 31P and 23Na NMR spectroscopy. Short-term effect of gossypol on phosphate metabolism in immobilized and perfused cells was apparent in 31P NMR spectra only with relatively high concentrations of gossypol, corresponding to about 40 times IC50. However, incubation with low gossypol concentrations markedly affected the energetic status of the cells, especially of the TM3 cells. Although inhibition of proliferation by gossypol was stronger with the TM4 cells, the decrease of intracellular ATP level and increase of sodium ion concentration were more pronounced in the TM3 cells. The growth-inhibitory effect of (-)-gossypol was stronger than that of (+)-gossypol, with the eudesmic ratio of 2-2.5. The enantioselectivity of the effect of gossypol on the energy metabolism of TM3 and TM4 cells was low, in contrast to the in vivo antispermatogenic effect, which was reported to be solely associated with (-)-gossypol. Inhibition of energy production in somatic testicular tissue is thus unlikely to be major cause of the antispermatogenic effect of gossypol.

In vivo Na-23 MR imaging and spectroscopy of rat brain during TmDOTP5- infusion

In vivo sodium-23 and hydrogen-1 magnetic resonance (MR) imaging and spectroscopy of the rat brain during infusion of the shift reagent thulium DOTP5- (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetra[methylene phosphonate] was performed to assign the various peaks observed during infusion and to evaluate the shift reagent in discriminating tissue compartments. Na-23 spectra collected during the infusion showed two shifted peaks that were assigned to intravascular Na+ and extracellular muscle Na+, respectively, and one unshifted peak assigned to intra- and extracellular brain Na+ and cerebrospinal fluid Na+. These assignments were validated with H-1 and Na-23 MR imaging and Na-23 chemical shift imaging (CSI). The H-1 and Na-23 images showed that a surface coil placed on a rat head can detect a substantial amount of signal from muscle surrounding the skull. Na-23 CSI spectra from successive 1-mm-thick coronal sections indicated that the shift reagent did not cross the blood-brain barrier. The study also showed that bulk susceptibility shifts are quite small with Tm-DOTP5-. This reagent may be useful in determining compartmental Na+ concentrations and blood flow kinetics in brain and in examining the integrity of the blood-brain barrier.

Variable NMR visibility of intracellular sodium induced by Na(+)-substrate cotransport in dog cortical tubules

The intracellular sodium concentration [( Na+]i) of dog kidney cortical tubules was monitored by flame photometry and 23Na NMR using dysprosium tripolyphosphate as shift reagent. Upon addition of substrates cotransported with sodium, flame photometry showed an increase in [Na+]i while no change (glutamine, glucose) or even a decrease (lactate) in the Na+i NMR signal was observed. This discrepancy could not be explained by a lack of ATP prior to the addition of substrates or by a decrease of NMR visibility of Nai+ induced by binding of substrate to membrane transporters (and pump). We propose that a variation of the "apparent visibility" of Nai+ may occur, arising from either a compartmentation of Nai+ in dog cortical tubules or an inhomogeneous extracellular distribution of the shift reagent.

A review of 23Na nuclear magnetic resonance spectroscopy for the in vitro study of cellular sodium metabolism

Changes in intracellular sodium have been associated with a number of different diseases. Consequently, various methods have been used to quantify the level of intracellular sodium concentrations. Traditional methods like flame photometry and ion-selective electrodes are destructive or invasive, thereby potentially altering the intracellular sodium levels. There has been an increasing interest in evaluating the method of 23Na nuclear magnetic resonance in recent years, since this method allows for non-invasive continuous monitoring of intracellular sodium in cell suspensions and tissues. A phenomenological approach to basic theory, review of methodology, applications to the in vitro study of cellular sodium metabolism, and difficulties of interpretation of this analytical modality is presented.

Erythrocyte Na+/K+ ATPase activity measured with 23Na NMR

A 23Na NMR assay for measurement of erythrocyte Na+/K+ ATPase activity is presented. Using the nonpermeant shift reagent dysprosium tripolyphosphate the signals of intra- and extracellular sodium are separated, enabling measurement of sodium fluxes nondestructively, without the need to physically separate the cells from their environment. By increasing membrane permeability with nystatin we have shown that the assay allows the detection of differences in membrane permeability. With low doses of nystatin the ouabain-sensitive sodium flux increased more than twofold. With high doses of nystatin the Na+/K+ pump could not prevent an almost total equilibration of intra- and extracellular sodium. All sodium that entered the cells remained NMR visible, proving that sodium influx can be measured quantitatively. 31P NMR spectra taken before and after the assay revealed a slight acidification of the cells and no significant change in ATP concentration. No evidence of Dy3+ entering the cell was observed.