Progressive enzyme changes within anatomically defined segments of rabbit nephron: demonstration with a new technique.

1988 ◽  
Vol 36 (3) ◽  
pp. 285-289 ◽  
Author(s):  
B R Cole ◽  
J G Boylan ◽  
T E Bross ◽  
H B Burch ◽  
O H Lowry
Keyword(s):  
Proximal Tubule ◽  
High Energy ◽  
Glycolytic Enzyme ◽  
Enzyme Assays ◽  
Abrupt Changes ◽  
Gluconeogenic Enzyme ◽  
A New Technique ◽  
Serial Samples ◽  
High Energy Phosphate Metabolism ◽  
Enzyme Changes

The kidney is an extremely heterogeneous organ, with morphological, physiological, and metabolic changes occurring from segment to segment along each nephron. To determine the heterogeneity that might exist within discrete anatomical segments of rabbit nephron, we developed a technique for making quantitative enzyme assays in serial samples, about 100 micron long, along identified segments of the nephron. Results for three enzymes in proximal convoluted and straight tubules show that adenylate kinase, an enzyme of high-energy phosphate metabolism, gradually decreases along the S1 and S2 segments of the proximal tubule, with no abrupt changes. Fructose bisphosphatase, a gluconeogenic enzyme, is high along the major portion of the proximal tubule but plummets along the final millimeter of S3. Conversely, phosphofructokinase, a glycolytic enzyme, is very low along the proximal tubule but increases sharply within the final millimeter. These data underscore the biochemical heterogeneity of the nephron, illustrating the enzyme levels may change markedly even within anatomically defined regions. They also suggest the importance of further studies of this type and demonstrate a practical means for such studies.

Synchronized Periodic Solutions of a Class of Periodically Driven Nonlinear Oscillators

1988 ◽  
Vol 55 (3) ◽  
pp. 721-728 ◽  
Author(s):  
Gamal M. Mahmoud ◽  
Tassos Bountis
Keyword(s):  
Periodic Solutions ◽  
Periodic Orbits ◽  
Nonlinear Oscillators ◽  
High Energy ◽  
Second Order ◽  
Multiple Time ◽  
Particle Beams ◽  
Periodically Driven ◽  
Time Scaling ◽  
A New Technique

We consider a class of parametrically driven nonlinear oscillators: x¨ + k1x + k2f(x,x˙)P(Ωt) = 0, P(Ωt + 2π) = P(Ωt)(*) which can be used to describe, e.g., a pendulum with vibrating length, or the displacements of colliding particle beams in high energy accelerators. Here we study numerically and analytically the subharmonic periodic solutions of (*), with frequency 1/m ≅ √k1, m = 1, 2, 3,…. In the cases of f(x,x˙) = x3 and f(x,x˙) = x4, with P(Ωt) = cost, all of these so called synchronized periodic orbits are obtained numerically, by a new technique, which we refer to here as the indicatrix method. The theory of generalized averaging is then applied to derive highly accurate expressions for these orbits, valid to the second order in k2. Finally, these analytical results are used, together with the perturbation methods of multiple time scaling, to obtain second order expressions for regions of instability of synchronized periodic orbits in the k1, k2 plane, which agree very well with the results of numerical experiments.

Differential energetic response of brain vs. skeletal muscle upon glycemic variations in healthy humans

2008 ◽  
Vol 294 (1) ◽  
pp. R12-R16 ◽  
Author(s):  
Kerstin M. Oltmanns ◽  
Uwe H. Melchert ◽  
Harald G. Scholand-Engler ◽  
Maria C. Howitz ◽  
Bernd Schultes ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Underlying Mechanism ◽  
High Energy ◽  
Resonance Spectroscopy ◽  
Energy Status ◽  
High Energy Phosphate ◽  
Available Energy ◽  
Healthy Humans ◽  
High Energy Phosphate Metabolism ◽  
The Brain

The brain regulates all metabolic processes within the organism, and therefore, its energy supply is preserved even during fasting. However, the underlying mechanism is unknown. Here, it is shown, using 31P-magnetic resonance spectroscopy that during short periods of hypoglycemia and hyperglycemia, the brain can rapidly increase its high-energy phosphate content, whereas there is no change in skeletal muscle. We investigated the key metabolites of high-energy phosphate metabolism as rapidly available energy stores by 31P MRS in brain and skeletal muscle of 17 healthy men. Measurements were performed at baseline and during dextrose or insulin-induced hyperglycemia and hypoglycemia. During hyperglycemia, phosphocreatine (PCr) concentrations increased significantly in the brain ( P = 0.013), while there was a similar trend in the hypopglycemic condition ( P = 0.055). Skeletal muscle content remained constant in both conditions ( P > 0.1). ANOVA analyses comparing changes from baseline to the respective glycemic plateau in brain (up to +15%) vs. muscle (up to −4%) revealed clear divergent effects in both conditions ( P < 0.05). These effects were reflected by PCr/Pi ratio ( P < 0.05). Total ATP concentrations revealed the observed divergency only during hyperglycemia ( P = 0.018). These data suggest that the brain, in contrast to peripheral organs, can activate some specific mechanisms to modulate its energy status during variations in glucose supply. A disturbance of these mechanisms may have far-reaching implications for metabolic dysregulation associated with obesity or diabetes mellitus.

Protective effects of adenosine in the perfused rat heart: changes in metabolism and intracellular ion homeostasis

1993 ◽  
Vol 264 (4) ◽  
pp. C986-C994 ◽  
Author(s):  
T. A. Fralix ◽  
E. Murphy ◽  
R. E. London ◽  
C. Steenbergen
Keyword(s):  
Cell Injury ◽  
Recovery Of Function ◽  
Ion Homeostasis ◽  
High Energy ◽  
Left Ventricular ◽  
Protective Effects ◽  
Intracellular Ca ◽  
Developed Pressure ◽  
High Energy Phosphate Metabolism ◽  
Glycolytic Rate

Increased concentrations of intracellular H+, Na+, and Ca2+ have been observed during ischemia, and these ionic alterations have been correlated with several indexes of cell injury in a number of studies. Recently, adenosine was proposed to play a role in ischemic preconditioning, since adenosine antagonists block the protective effects of these brief intermittent periods of ischemia and reflow. In this study we evaluated the protective effects of adenosine (20 microM) on high-energy phosphate metabolism, H+ and Ca2+ accumulation, and glycolytic rate during 30 min of no-flow ischemia. Adenosine was observed to slow the onset of contracture (7.0 +/- 0.9 min) and to improve left ventricular developed pressure (62 +/- 7% of initial) during reperfusion compared with untreated hearts (5.0 +/- 0.6 min and 18 +/- 5%, respectively). Intracellular Ca accumulation at the end of 30 min of ischemia was higher in the untreated (2,835 +/- 465 nM) than in the adenosine-treated (2,064 +/- 533 nM) hearts, while intracellular pH fell more in the untreated (5.85 +/- 0.17) than in the adenosine-treated hearts (6.27 +/- 0.16). Glycolytic rate and the rate of ATP decline were significantly attenuated in the adenosine-treated hearts during ischemia. Thus adenosine treatment slowed the rate of metabolism and delayed the accumulation of H+ and Ca2+ during ischemia, resulting in better recovery of function upon reflow.

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