Biomedical subjects

M J Avison

Publications and source records attributed to M J Avison.

42 records · Page 3Linked to original sources

PubMed1986

Postischemic ATP-MgCl2 provides precursors for resynthesis of cellular ATP in rats.

Postischemic administration of ATP-MgCl2 is known to enhance recovery of renal function and accelerate the restitution of cellular ATP levels. To differentiate between a direct and indirect effect of the exogenous nucleotide, rats were subjected to 45 min of bilateral renal ischemia and were infused with either ATP-MgCl2, AMP-MgCl2, or normal saline. The immediate recovery of the cellular ATP was similar in all three groups of animals, whereas the subsequent recovery was accelerated by the infusion of either nucleotide. Since ATP-MgCl2 and AMP-MgCl2 produced similar results, this study provides evidence that exogenous ATP may act by providing precursors for the resynthesis of the cellular adenine nucleotide pool rather than being a direct source of energy.

Adenosine Triphosphate↗

PubMed1985

1H homonuclear editing of rat brain using semiselective pulses.

We have used a semiselective Hahn spin-echo sequence of the form (1331)-tau-(2662)-tau-AQ, delivered by a surface coil to obtain high-resolution 1H NMR spectra from the brains of intact dead rats. This sequence gave suppression of the tissue water resonance by a factor of 80,000 when tau = 68 ms. Delivery of a frequency-selective Dante pulse train to the alpha-CH resonance of lactate at 4.11 ppm, simultaneously with the 2662 refocusing pulse, altered the j-modulation in the spin-coupled beta-CH3 protons. Subtraction of this spectrum from one in which the Dante was ineffective gave an edited spectrum containing only the beta-CH3 resonance of lactate at 1.31 ppm. When the position of the Dante was shifted to 3.78 ppm to selectively invert the alpha-CH protons of alanine, an edited spectrum of alanine was obtained.

Alanine↗

PubMed1985

23Na and 39K NMR studies of ion transport in human erythrocytes.

Ion transport in human erythrocytes was studied by 23Na and 39K NMR with an anionic paramagnetic shift reagent, Dy(P3O10)2(7-). The intra- and extracellular 23Na and 39K NMR signals were well separated (over 10 ppm) at 5 mM concentration of the shift reagent. The NMR visibility of the intracellular Na+ and K+ was determined to be 100% in human and duck erythrocytes. The intracellular ion concentrations were 8.1 +/- 0.8 mM Na+ (n = 7) and 110 +/- 12 mM K+ (n = 4) for fresh human erythrocytes. The ouabain-sensitive net Na+ efflux was 1.75 +/- 0.08 mmol/hr per liter of cells at 37 degrees C (n = 3). The gramicidin-induced ion transport in human erythrocytes was also studied by 23Na and 39K NMR or by simultaneous measurements of 23Na NMR and a K+-selective electrode. The time courses of the Na+ and K+ transport induced by the ionophore were biphasic. The initial rapid fluxes were due to an exchange of Na+ for K+, which were found to occur with a 1:1 stoichiometry. The subsequent slow components were the net Na+ and K+ effluxes rate-limited by the Cl- permeability and accompanied by a reduction in cell volume. The Cl- permeability determined from the NMR measurements of these slow fluxes was 3.2 +/- 0.5 X 10(-8) cm/sec at 25 degrees C (n = 4).

Biological Transport, Active↗

PubMed1985

NMR measurements of intracellular sodium in the rabbit proximal tubule.

The present study evaluated the use of nuclear magnetic resonance (NMR) spectroscopy to monitor directly and continuously intracellular sodium levels in rabbit renal cortical tubule suspensions. When the paramagnetic shift reagent dysprosium tripolyphosphate was added to the extracellular medium it was possible to resolve signals from intracellular and extracellular sodium without adversely affecting cellular viability. An efflux of intracellular sodium against a significant concentration gradient was observed when sodium-loaded cells were warmed from 4 to 37 degrees C. At 37 degrees C in steady state, inhibition of Na+-K+-ATPase activity by ouabain increased intracellular sodium content in a dose-dependent and time-dependent manner. A biphasic time course of increased intracellular sodium following ouabain (10(-3) M) suggested that the sodium permeability of the plasma membrane may decrease following pump inhibition, thus limiting sodium influx. Nystatin, an agent known to facilitate sodium entry across cell membranes, increased intracellular sodium fivefold. In another series of experiments several maneuvers were performed to ascertain the fraction of intracellular sodium that was NMR visible. Quantitative assessment of either an efflux or influx of sodium indicated that the NMR visibility of the transported sodium was 100%. Furthermore, disruption of the cell membranes with Triton X-100 showed that the entire pool of intracellular sodium was 100% NMR visible.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1983

Enhanced recovery of renal ATP with postischemic infusion of ATP-MgCl2 determined by 31P-NMR.

The postischemic infusion of ATP-MgCl2 will enhance the recovery of both glomerular and tubular function. To assess the effect of ATP-MgCl2 on tissue nucleotides, 31P nuclear magnetic resonance (31P-NMR) spectra were obtained continuously in vivo from the left kidney of rats that had been subjected to 45 min of renal ischemia and then infused with either normal saline or ATP-MgCl2. 31P-NMR spectra with distinct peaks for alpha-, beta-, and gamma-phosphate of ATP, sugar phosphate, and inorganic phosphate were collected every 7 min before, during, and after renal artery occlusion. During ischemia, the ATP beta-peak (the only peak unique to ATP) fell rapidly to 10% of control values in both groups of animals. By 120 min after the ischemic insult, the animals treated with ATP-MgCl2 had recovery of renal ATP to 89 +/- 2.6%, which is significantly greater (P less than 0.001) than 65.2 +/- 1.8% found in rats given normal saline. These data indicate that 1) 31P-NMR can be used to assess renal ATP levels continuously in vivo; 2) during renal ischemia ATP levels fall quickly to less than 10% of control values; 3) tissue ATP returns relatively slowly to control values in rats given normal saline, whereas postischemic treatment with ATP-MgCl2 results in an accelerated recovery of tissue ATP levels. These findings provide a biochemical correlate to the improvement in renal function previously described.

Adenosine Triphosphate↗

PubMedDate not supplied

Brain creatine kinase with aging in F-344 rats: analysis by saturation transfer magnetic resonance spectroscopy.

We measured in vivo forward flux of the creatine kinase reaction in rat forebrain in young (Y: 6 month, n = 13), mid-aged (M: 12 month, n = 7) and aged (O: 27 month, n = 10) animals using 31P magnetic resonance saturation transfer. Forward flux was reduced in the aged rats (Y: 0.42 +/- 0.08; M: 0.41 +/- 0.10; O: 0.31 +/- 0.03 s(-1) +/- SD; p = 0.008 O vs. Y). In vitro studies in a subset of the same rats showed a parallel decline in CK activity (Y: 2.16 +/- 0.40; M: 2.17 +/- 0.25; O: 1.56 +/- 0.06 IU +/- S.D.; p = 0.002 O vs. Y). The in vivo spectroscopic and in vitro biochemical measures were significantly correlated. Reduced creatine kinase activity could account for the observed decreased forward flux in aging brain. Intracellular pH, phosphocreatine/inorganic phosphate ratio, and phospocreatine/gamma-adenosine triphosphate ratio did not differ between groups. Forward flux may represent a better measure of brain energy function than relative phosphocreatine or adenosine triphosphate levels observable in vivo.

Aging↗