Enzymatic activities in slow and fast denervated old rat muscles

The activities of five enzymes have been studied quantitatively in denervated extensor digitorum longus, gastrocnemius and soleus muscles of 24-month-old rats. The results have been compared with those obtained from normal muscles of a similar age group of rats. Three weeks after denervation, the activity of hexokinase was increased in gastrocnemius and extensor digitorum longus. Phosphofructokinase, lactate dehydrogenase, malate dehydrogenase and 3-hydroxyacyl-CoA-dehydrogenase showed decreased activities. These results suggest that enzyme which represents glucose uptake increased its activity in fast muscles and that enzymes for anaerobic glycolysis, lactate fermentation, citric acid cycle and beta-oxidation had a decreased activity in slow and fast muscles.     

Comparison of enzyme activities on glycogen metabolism in rabbit slow and fast muscles

Activities of glycogen synthase (total) and branching enzyme in slow (soleus) muscle are higher than those in fast (vastus lateralis) muscle, while those of phosphorylase kinase (total), phosphorylase (total) and debranching enzyme are reversed. The active form ratio of glycogen synthase is higher in fast muscle, while those of phosphorylase kinase and phosphorylase are higher in slow muscle. Activities of cAMP-dependent protein kinase and protein phosphatase in slow muscle are higher than those in fast muscle. These results suggest that glycogen metabolizing enzymes in slow muscle, distinct from those in fast muscle, are regulated more strongly by cAMP-dependent protein kinase rather than by protein phosphatase.     

Cytoplasm-to-myonucleus ratios and succinate dehydrogenase activities in adult rat slow and fast muscle fibers

The relationship between myonuclear number, cellular size, succinate dehydrogenase activity, and myosin type was examined in single fiber segments (n = 54; 9 ± 3 mm long) mechanically dissected from soleus and plantaris muscles of adult rats. One end of each fiber segment was stained for DNA before quantitative photometric analysis of succinate dehydrogenase activity; the other end was double immunolabelled with fast and slow myosin heavy chain monoclonal antibodies. Mean ± S.D. cytoplasmic volume/myonucleus ratio was higher in fast and slow plantaris fibers (112 ± 69 vs. 34 ± 21 x 10 ³µm ³) than fast and slow soleus fibers (40 ± 20 vs. 30 ± 14 x 10 ³µm ³), respectively. Slow fibers always had small volumes/myonucleus, regardless of fiber diameter, succinate dehydrogenase activity, or muscle of origin. In contrast, smaller diameter (<70 µm) fast soleus and plantaris fibers with high succinate dehydrogenase activity appeared to have low volumes/myonucleus while larger diameter (>70 µm) fast fibers with low succinate dehydrogenase activity always had large volume/myonucleus. Slow soleus fibers had significantly greater numbers of myonuclei/mm than did either fast soleus or fast plantaris fibers (116 ± 51 vs. 55 ± 22 and 44 ± 23), respectively. These data suggest that the myonuclear domain is more limited in slow than fast fibers and in the fibers with a high, compared to a low, oxidative metabolic capability.     

Evaluation of RNA polymerase activities in nuclei isolated from slow and fast skeletal muscles

The optimal incubation conditions were determined for the assay of the α-amanitin-resistant, DNA-dependent RNA polymerase A and the α-amanitin-sensitive, DNA-dependent RNA polymerase B in nuclei isolated from rat skeletal muscles. Significantly higher levels of activity of RNA polymerase B were found in the nuclei isolated from the slow-twitch soleus compared with nuclei from the fast-twitch extensor digitorum longus.     

Learning,fast and slow

Animals can learn efficiently from a single experience and change their future behavior in response. However, in other instances, animals learn very slowly, requiring thousands of experiences. Here, I survey tasks involving fast and slow learning and consider some hypotheses for what differentiates the underlying neural mechanisms. It has been proposed that fast learning relies on neural representations that favor efficient Hebbian modification of synapses. These efficient representations may be encoded in the genome, resulting in a repertoire of fast learning that differs across species. Alternatively, the required neural representations may be acquired from experience through a slow process of unsupervised learning from the environment.     

Optimal specificity and function for flexible biomolecular recognition

Biomolecular associations often accompanied by large conformational changes, sometimes folding and unfolding. By exploring an exactly solvable model, we constructed the free energy landscape and established a general framework for studying the biomolecular flexible binding process. We derived an optimal criterion for the specificity and function for flexible biomolecular binding where the binding and conformational folding are coupled.     

Quantifying the kinetic paths of flexible biomolecular recognition

Biomolecular recognition often involves large conformational changes, sometimes even local unfolding. The identification of kinetic pathways has become a central issue in understanding the nature of binding. A new approach is proposed here to study the dynamics of this binding-folding process through the establishment of a path-integral framework on the underlying energy landscape. The dominant kinetic paths of binding and folding can be determined and quantified. The significant coupling between the binding and folding of biomolecules often exists in many important cellular processes. In this case, the corresponding kinetic paths of binding are shown to be intimately correlated with those of folding and the dynamics becomes quite cooperative. This implies that binding and folding happen concurrently. When the coupling between binding and folding is weak (strong), the kinetic process usually starts with significant folding (binding) first, with the binding (folding) later proceeding to the end. The kinetic rate can be obtained through the contributions from the dominant paths. The rate is shown to have a bell-shaped dependence on temperature in the concentration-saturated regime consistent with experiment. The changes of the kinetics that occur upon changing the parameters of the underlying binding-folding energy landscape are studied.     

Enzymatic activities and ATP-induced fluorescence enhancement of myosin from fast and slow skeletal and cardiac muscles.

The maximal ATP-induced enhancement of fluorescence and the dependence of this enhancement on ATP concentration were determined for myosins from fast and slow skeletal and cardiac muscle of the rabbit. With myosins from slow and cardiac muscle modifications in the preparative procedure and chromatography on DEAE-Sephadex were required to obtain preprations which were free of actin, which exhibited the maximal fluorescence enhancement and which bound two moles of ATP per mole of myosin. Since the fluorescence enhancement of cardiac and slow muscle myosins is labile at slightly alkaline pH, it was also necessary to minimize incubation at pH greater than 7 in order to attain the maximal enhancement. With fast muscle myosin the changes in preparative procedure, together with chromatography, led to a 50 to 100% increase in the steady-state rate of ATP hydrolysis and fluorescence enhancement, without changing the maximal binding of ATP. From a comparison of the rate of steady-state hydrolysis of ATP with the rate of decay of the enhanced fluorescence, it appears that for all three myosins, both ATP binding sites have the same enzymatic activity, the steady-state rate per site being slower for cardiac and slow muscle myosins than for fast muscle myosin.     

The effect of torbafylline on enzyme activities in fast and slow muscles with limited blood supply.

1. Activities of a glycolytic enzyme--lactate dehydrogenase, LDH, and two oxidative enzymes--citrate synthase (CS), a marker for TCA cycle entry, and 3-hydroxyacyl-CoA dehydrogenase (HAD), which indicates the capacity for beta-oxidation of endogenous lipids, were measured in fast (tibialis anterior, TA, and extensor digitorum longus, EDL) and slow (soleus, SOL) muscles of Sprague-Dawley rats with intact and limited blood supply, and following treatment with the xanthine derivative torbafylline (Hoechst, Werk Albert, Wiesbaden). 2. Limitation of blood supply by unilateral ligation of the common iliac artery increased activity of LDH in fast muscles, and activity of CS and HAD in soleus. 3. Torbafylline treatment caused an increased LDH activity in intact fast muscles and decreased it in soleus, although the relative capacity for anaerobic and aerobic metabolism (indicated by the ratio of LDH and CS activities) remained unchanged in all cases. 4. Whilst having little effect on oxidative enzyme activity of fast muscles, torbafylline decreased the activity of CS but increased activity of HAD in soleus, suggesting a greater reliance on lipid metabolism. 5. The effect of arterial ligation on enzyme activity was ameliorated by treatment with torbafylline, possibly due to its effect on the microcirculation.     

Analysis of genetic variation affecting the relative activities of fast and slow ADH dimers in Drosophila melanogaster heterozygotes

When Adh ^F /Adh ^S heterozygote homogenates are stained after electrophoresis, considerable variation is observed in the activity ratio of the FF dimer to the SS dimer. Two Adh ^S strains showed a sharp, consistent difference when crossed to a common Adh ^F strain. Optical scanning and genetic analysis confirmed that this difference originates close to the Adh locus. Since the morphs varied concordantly in their activities on numerous alcohols, and since aging and heat-treatment experiments failed to reveal a stability difference, it is proposed that the difference is regulatory in nature, affecting ADH synthesis and primarily cis-acting. A survey of wild flies revealed additional variation in the FF/SS activity ratio. Further genetic analysis showed that the basis of this variation is not restricted to the second chromosome. Furthermore, modification of the activity ratio implies some degree of allelespecificity on the part of the modifiers.This work was supported in part by money collected by Jewish Community of Iowa City, Iowa, and by NSF Grant 76-01903 to Roger Milkman.     

Differentiation of slow and fast muscles in chickens

1. The development of the characteristic histochemical appearance of the slow anterior latissimus dorsi (ALD) and fast posterior latissimus dorsi (PLD) was studied in chickens during embryonic development as well as during regeneration of minced muscle. 2. During embryonic development the activity of the oxidative enzyme succinic dehydrogenase (SDH) is higher in the slow ALD muscle already at 16 days of incubation. At this time the fast PLD has a higher activity of the glycolytic enzyme, phosphorylase. Although the histochemical appearance of the two types of muscle is already different at 16 days, their contractile speeds are still similar. No difference in myosin ATP-ase was found in the two muscles in young embryos but in 20-day old embryos the two muscles became distinctly different when stained for this enzyme. 3. When PLD muscles in hatched chickens redeveloped during regeneration in place of ALD the histochemical characteristics of the regenerated muscle resembled ALD, and when ALD regenerated in place of PLD it resembled PLD. 4. It is concluded that the histochemical characteristics of slow and fast muscles become determined during early development, even before any difference in contractile properties can be detected and that they are determined by the nerve.     

Effects of taxol on slow and fast axonal transport

Axonal transport of tubulin in the rat sciatic nerve is almost completely inhibited by a single subepineural injection of taxol, without affecting that of neurofilament proteins. Actin and a large number of polypeptides cotransported with actin as minor components are also blocked by taxol, although to a lesser extent. Fast axonal transport is essentially free from the inhibitory effect of this drug. Although previous models have suggested that slow axonal transport involves the bulk movement of cytoskeletal structures, these results suggest that such transport may involve an equilibrium between polymerised and depolymerised forms of the axonal cytoskeleton.     

Disopyramide phosphate effects on slow and depressed fast responses

We studied the effects of disopyramide phosphate on explanted neonatal rat ventricle cells exhibiting depressed fast responses or naturally occurring slow response action potentials together with automatic activity. Disopyramide suppressed the spontaneous activity at a concentration of 2.5 micrograms/mL with a half-maximal value of 10 micrograms/mL. Before spontaneous activity was lost, there was an increase in beating rate possibly related to membrane depolarization. In depressed fast and slow response action potentials there was an increase in action potential duration (APD) which was consistently found both at the level of the plateau and at 90% repolarization. Comparison of the APD increase observed after disopyramide treatment and that after exposure to 20 mM tetraethylammonium suggested a block of a potassium conductance as a possible cause underlying the change in APD. The Vmax values of the depressed fast response decreased at constant membrane potential and this was attributed to the local anesthetic effect of the drug. In addition, we report two novel findings: (i) a decrease of Vmax of the slow response action potentials which may be secondary to membrane depolarization, and (ii) an increase in the duration of slow action potentials, possibly caused by inhibition of a potassium conductance.