Comparison of calcium release from sarcoplasmic reticulum of slow and fast twitch muscles

Summary It is shown that equations developed to analyze the contributions of secondary active transport processes to symmetrical cells (Gordon, L. G. M., Macknight, A. D. C., 1991,J. Membrane Biol. 120: 139–152) can be used, with minor modifications, to analyze the steady-state membrane potential in epithelia under the unique situation of short circuiting. Only under such conditions is there a single intracellular potential relative to both the mucosal and serosal media. The equations are investigated in relation to a model tight epithelium—the toad urinary bladder. It is shown that the properties of the membrane transport pathways are such that the intracellular potential under short-circuit conditions must be more negative than often reported. Given measurements of membrane potential and of voltage-divider ratio, it is possible to use the equations to estimate the absolute values of the membrane permeabilities and conductances under shortcircuit conditions.     

Some characteristics of myotubes cultured from slow and fast chick muscles

Explant cultures were prepared from the slow anterior latissimus dorsi muscle and the fast posterior latissimus dorsi muscle of 15 day chick embryos. The morphology and growth pattern of myotubes from the two types of muscle were very similar. Intracellular microelectrode studies did not reveal consistent differences between the myotube types in regard to resting potential, input resistance, input time constant, or ability to produce active electrogenic responses. It is suggested that specific differentiation of the two muscles is determined by their innervation.     

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.     

The fine structure of fast and slow crustacean muscles

Known phasic and tonic muscle fibers of the crab Cancer magister were studied by electron microscopy. Phasic fibers have sarcomeres about 4.5 µ long, small polygonal myofibrils, and a well-developed sarcoplasmic reticulum. The thick myofilaments, disposed in hexagonal array, are each surrounded by six thin filaments. The tonic fibers have a sarcomere length of about 12 µ, larger myofibrils, a poorly developed sarcoplasmic reticulum, and a disorderly array of myofilaments. Each thick myofilament is surrounded by 10–12 thin filaments. The same morphological type of slow muscle has been found in the crustaceans, Macrocyclops albidus, Cypridopsis vidua, and Balanus cariosus, in each case in an anatomical location consistent with tonic action. A search of the literature indicates that this type of muscle is found in all classes of arthropods and is confined to visceral and postural muscles or specializations of these.     

Motor and sensory reinnervation of fast and slow mammalian muscles

Summary 1. The formation of endplates outside the original endplate region of a muscle fibre was studied in slow and fast rat muscles. It was found that such new endplates are readily formed on the soleus muscle, whereas hardly at all in the fast extensor digitorum longus. Most new endplates appear to be morphologically normal within 2 months after nerve implantation.2. The time course of recovery of slow and fast cat muscles was followed after crushing the sciatic nerve. It was found that the slow soleus muscle recovers more rapidly than the fast flexor hallucis longus muscle.3. The endplates of reinnervated cat muscles are more complicated than those of the control muscles, but have nevertheless fewer nerve terminals per endplate. Reinnervated muscles are more sensitive to curare and it is suggested that this is due to a decrease in transmitter release, for it was found that less acetylcholine is released from reinnervated rat hemidiaphragms than from control ones.4. Motor and sensory reinnervation of spindles and tendon organs was studied. At the time when motor reinnervation is almost completed the sensory endings from spindles and tendon organs are highly abnormal. Thus sensory reinnervation proceeds much more slowly than motor.     

A comparative study of muscle spindles in slow and fast neonatal muscles of normal and dystrophic mice

Muscle spindles from the slow-twitch soleus and the fast-twitch extensor digitorum longus (EDL) muscles of genetically dystrophic mice of the dy2J/dy2J strain were compared with age-matched normal animals at neonatal ages of 1-3 weeks according to histochemical, quantitative, and ultrastructural parameters. Intrafusal fibers in both the soleus and EDL exhibited similar regional differences in myosin ATPase activity, and conformed to those noted previously in various adult species. In distal polar regions, all nuclear bag fibers resembled extrafusal fibers of the type 1 variety, whereas in capsular zones they could be divided into two subtypes. Nuclear chain fibers possessed a staining pattern similar to type 2 extrafusal fibers, and in contrast to the bag fibers they exhibited no regional variations. These features were consistently observed in both the normal and dystrophic muscles at all ages. Spindles varied only slightly in their number and distribution in the two types of muscle, and their location followed the neurovascular branching pattern in each. Irrespective of age or genotype, spindles in the soleus were more homogeneously dispersed, but those in the EDL were concentrated along the dorsal aspect of the muscle. No significant differences were noted in the total number of spindles between normal and dystrophic muscles. In addition, no dramatic differences were observed in the muscle spindle index for soleus and EDL. The first obvious disease-related changes were noted in extrafusal fibers of the soleus of 3-week-old mice, and spindles were often located close to these areas of fiber degeneration. Despite alterations in the surrounding tissue, however, spindles appeared morphologically unaltered in dystrophy. These observations indicate that intrafusal fibers of spindles in neonatal mice appear enzymatically and histologically unaffected in incipient stages of progressive muscular dystrophy.     

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.     

Activity of some enzymes of energy metabolism during denervation and reflex atrophy in rat slow and fast muscles

The loss of muscle weight in the soleus (SOL) and extensor digitorum longus (EDL) muscles was compared after denervation and in the course of reflex muscle atrophy induced by unilateral fracture of metatarsal bones of the paw and local injection of 0.02 ml turpentine oil subcutaneously. This so-called reflex atrophy is significantly greater after 3 days than that after denervation. Seven days after the nociceptive stimulus, reflex and denervation atrophy are grossly similar in both muscles. This also applies in case that the nociceptive stimulus had been repeated on the third day. The EDL:SOL enzyme activities of energy supply metabolism reflect the differences between a glycolytic-aerobic (EDL) and predominantly aerobic type (SOL) of muscle. No consistent changes were found in either type of atrophy after 3 days. In 7 days' denervation, the activity of hydroxyacetyl-CoA-dehydrogenase (HOADH) and citrate synthase (CS) was decreased in the SOL, while glycerolphosphate:NAD dehydrogenase (GPDH) was enhanced. In the EDL, the activity of triosephosphate dehydrogenase (TPDH), GPDH, malate dehydrogenase (MDH), CS and HOADH was decreased. Acid phosphatase (AcP) was greatly increased in both muscles. Seven days after application of the nociceptive stimulus, all enzyme activities were altered in a grossly analogous manner as after denervation.     

Effects of clofibrate on basal and insulin-activated glucose uptake in fast and slow skeletal muscles of rats.

1. The basal uptake of glucose was increased significantly in the extensor digitorum longus muscle (EDL) of rats by clofibrate administration. 2. The insulin-activated uptake of glucose was increased in the soleus muscle (Sol) by clofibrate. 3. The insulin-induced increment of glucose uptake was increased significantly in Sol and decreased significantly in EDL by clofibrate.     

Effects of adenosine 3':5'-monophosphate-dependent protein kinase on sarcoplasmic reticulum isolated from cardiac and slow and fast contracting skeletal muscles.

Effects of cyclic adenosine 3':5'-monophosphate (cyclic AMP)-dependent protein kinase were studied in sarcoplasmic reticulum prepared from cardiac and slow and fast (white) skeletal muscle. Cyclic AMP-dependent protein kinase failed to catalyze phosphorylation of fast skeletal muscle microsomes as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Cyclic AMP-dependent protein kinase was without effect on calcium uptake by these microsomes. Treatment of cardiac microsomes obtained from dog, cat, rabbit, and guinea pig with cyclic AMP-dependent protein kinase and ATP resulted in phosphorylation of a 22,000-dalton protein component in the amounts of 0.75, 0.25, 0.30, and 0.14 nmol of phosphorus/mg of microsomal protein, respectively. Calcium uptake by cardiac microsomes was stimulated 1.8- to 2.5-fold when microsomes were treated with cyclic AMP-dependent protein kinase. Protein kinases partially purified from bovine heart and rabbit skeletal muscle were both effective in mediating these effects on phosphorylation and calcium transport in dog cardiac sarcoplasmic reticulum. Slow skeletal muscle sarcoplasmic reticulum also contains a protein with a molecular weight of approximately 22,000 that can be phosphorylated by protein kinase. Phosphorylation of this component ranged from 0.005 to 0.016 nmol of phosphorous/mg of microsomal protein in dog biceps femoris. A statistically significant increase in calcium uptake by these membranes was produced by the protein kinase. Increases in protein kinase-catalyzed phosphorylation of a low molecular weight microsomal component and in calcium transport by sarcoplasmic reticulum of cardiac and slow skeletal muscle may be related to the relaxation-promoting effects of epinephrine seen in these types of muscle. Conversely, the absence of a relaxation-promoting effect of epinephrine in fast skeletal muscle may be associated with the lack of effect of cyclic AMP and protein kinase on calcium transport by the sarcoplasmic reticulum of this type of muscle.     

Myosin from fast and slow skeletal and cardiac muscles of mammals of different size.

The ATPase activity of myosin and contraction time in extensor digitorum longus muscle, soleus muscle and cardiac muscle was compared in mammals differing in size. It was shown that the myosin ATPase activity of homologous muscles decreases and contraction time increases with increasing size of animals. The rate of tryptic digestion of myosin, the electrophoretic pattern of light chains of myosin and the effect of p-chloromercuribenzoate on ATPase activity of myosin were also studied. All these three myosin properties are very characteristic when the myosin from a fast muscle is compared with the myosin from a slow muscle of the same animal, but no relationship between these three myosin properties and ATPase activity of myosin was found, when homologous muscles of various mammals were compared.     

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.     

Nutrition and muscle potassium: differential effect in rat slow and fast muscles

The effects of malnutrition on intracellular K+ activity, (alpha K)i, and membrane potential, Em, were measured by means of double-barrelled K+-selective microlectrodes in the soleus and gastrocnemius muscles of the rat. (alpha K)i and Em were measured in vivo in normal anaesthetized animals and in rats subjected to one of two diet restrictions: a 2-day fast or a long-term hypocaloric diet. In the soleus muscle, (alpha K)i fell by similar amounts in both 2-day fasted and long-term hypocalorically fed rats, while Em depolarized significantly only in hypocalorically fed rats. In the gastrocnemius muscle, neither the 2-day fast nor the hypocaloric diet affected (alpha K)i or Em. It is suggested that the selective loss of K+ from the soleus muscle may be related to its activity pattern.     

Regulation of glucose uptake in rat slow and fast skeletal muscles

1. Regulation of glucose uptake was compared between extensor digitorum longus (EDL) and soleus (Sol) muscles in rats. 2. Insulin stimulated glucose uptake more in EDL than in Sol. 3. Under high concentrations of insulin, the glucose uptake was higher in EDL than Sol. 4. Inhibition of oxidative phosphorylation by anoxia or an uncoupler stimulated glucose uptake more in EDL than in Sol. 5. Anoxia abolished the effect of insulin on glucose uptake in both EDL and Sol. 6. The blocker to glucose transport system reduced glucose uptake more in Sol than in EDL.     

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.     

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.