Miniature potentials in fast and slow muscle fibers in locusts

Excitatory miniature postsynaptic potentials were studied by an intracellular recording method in fast and slow muscle fibers ofLocusta migratorioides. Statistical analysis showed that liberation of mediator in both types of fibers can be predicted by the formula for a negative binomial distribution with a probability of 85%. This correlation is evidence of some degree of interaction between consecutive liberations of quanta of mediator by nerve endings. It is shown that the fraction of miniature potentials depending on the external calcium concentration is greater in fast muscle fibers. An increase in the magnesium ion concentration from 2 to 40 mM led to a decrease in the frequency of miniature potentials, and this decrease was greater in fast fibers; an increase in the magnesium ion concentration from 1 to 10 mM in calcium-free solutions, on the other hand, led to some increase in frequency, and this also was greater in fast muscle fibers. It is concluded that nerve endings in fast and slow muscle fibers differ in their sensitivity to changes in the ionic composition of the medium.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 13, No. 2, pp. 210–217, March–April, 1981.     

Controlled differentiation of myoblast cells into fast and slow muscle fibers

Skeletal muscles are classified into fast and slow muscles, which are characterized by the expression of fast-type myosin heavy chains (fMyHCs) or slow-type myosin heavy chains (sMyHCs), respectively. However, the mechanism of subtype determination during muscle fiber regeneration is unclear. We have analyzed whether the type of muscle is determined in the myoblast cells or is controlled by the environment in which the muscle fibers are formed from myoblast cells. When myoblast cells from 7-day-old chick embryo were cultured and formed into muscle fibers, more than half of the fibers produced only fMyHCs, and the remaining fibers produced both fMyHCs and sMyHCs. However, when myoblast cells were cultured in medium supplemented with a small amount of slow muscle extract, the expression of sMyHCs in muscle fibers increased, whereas the expression of fMyHCs increased in the group supplemented with fast muscle extract compared with the control group. The same results were obtained when cloned mouse myoblast cells (C₂C₁₂ cells) were cultured and formed into muscle fibers. The data presented here thus show that the subtype differentiation of muscle fiber is controlled by the environment in which the muscle fiber forms. This work was funded by the Sasakawa Scientific Research Grant of the Japan Science Society.     

Neural regulation of mammalian fast and slow muscle myosins: an electrophoretic analysis.

Mammalian nerves to fast and slow muscles have the remarkable property of changing the speed of contraction of muscles following cross-reinnervation. The biochemical basis of speed transformation is the change in myosin in ATPase activity. This paper provides electrophoretic evidence for structural changes in myosin from cross-reinnervated muscles. A method is described for the separation of intact fast and slow muscle myosins by polyacrylamide gel electrophoresis. This method utilizes the fact that ATP and its analogs prevent the formation of myosin polymers in low ionic strength buffers. In this system, normal fast muscle myosin has a higher electrophoretic mobility than slow muscle myosin. Normal rat soleus myosin has a major slow and a minor fast component due to two populations of muscle fibers. The same muscle cross-reinnervated by a fast muscle nerve shows only the fast component, The normal, homogeneous fast extensor digitorum longus muscle has only the electrophoretically fast myosin, but following cross-reinnervation it shows both fast and slow components. These results suggest that mammalian motor nerves can induce or suppress the expression of genes that code for fast and slow skeletal muscle myosins.     

Development of ionic currents of zebrafish slow and fast skeletal muscle fibers

Voltage-gated Na+ and K+ channels play key roles in the excitability of skeletal muscle fibers. In this study we investigated the steady-state and kinetic properties of voltage-gated Na+ and K+ currents of slow and fast skeletal muscle fibers in zebrafish ranging in age from 1 day postfertilization (dpf) to 4-6 dpf. The inner white (fast) fibers possess an A-type inactivating K+ current that increases in peak current density and accelerates its rise and decay times during development. As the muscle matured, the V50s of activation and inactivation of the A-type current became more depolarized, and then hyperpolarized again in older animals. The activation kinetics of the delayed outward K+ current in red (slow) fibers accelerated within the first week of development. The tail currents of the outward K+ currents were too small to allow an accurate determination of the V50s of activation. Red fibers did not show any evidence of inward Na+ currents; however, white fibers expressed Na+ currents that increased their peak current density, accelerated their inactivation kinetics, and hyperpolarized their V50 of inactivation during development. The action potentials of white fibers exhibited significant changes in the threshold voltage and the half width. These findings indicate that there are significant differences in the ionic current profiles between the red and white fibers and that a number of changes occur in the steady-state and kinetic properties of Na+ and K+ currents of developing zebrafish skeletal muscle fibers, with the most dramatic changes occurring around the end of the first day following egg fertilization.     

How swimming fish use slow and fast muscle fibers: implications for models of vertebrate muscle recruitment

We quantified the intensity and duration of electromyograms (emgs) from the red and white axial muscles in five bluegill sunfish (Lepomis macrochirus) which performed three categories of behavior including steady swimming and burst and glide swimming at moderate and rapid speeds. Steady swimming (at 2 lengths/s) involved exclusively red muscle activity (mean posterior emg duration = 95 ms), whereas unsteady swimming utilized red and white fibers with two features of fiber type recruitment previously undescribed for any ectothermic vertebrate locomotor muscle. First, for moderate speed swimming, the timing of red and white activity differed significantly with the average onset time of white lagging behind that of red by approximately 40 ms. The durations of these white emgs were shorter than those of the red emgs (posterior mean = 82 ms) because offset times were effectively synchronous. Second, compared to steady and moderate speed unsteady swimming, the intensity of red activity during rapid unsteady swimming decreased while the intensity of white muscle activity (mean white emg duration = 33 ms) increased. Decreased red activity associated with increased white activity differs from the general pattern of vertebrate muscle recruitment in which faster fiber types are recruited in addition to, but not to the exclusion of, slower fiber types.     

Contractile proteins of fast and slow fibers during differentiation of lobster claw muscle

Contractile protein populations were determined, using gel electrophoresis, during development of the claw closer muscles of the lobster Homarus americanus. In the adult the paired claw closer muscles are asymmetric, consisting of a crusher muscle with all slow fibers and a cutter muscle with a majority of fast and a few slow fibers. The electrophoretic banding pattern of these adult fast and slow fibers shows a similarity in the major proteins including myosin, actin, and tropomyosin which are common to both fiber types. Paramyosin is slightly heavier in fast fibers than in slow. However, fast fibers have three proteins and slow fibers have four proteins which are unique to themselves. Several of these unique proteins belong to the regulatory troponin complexes. In juvenile 4th stage lobster, where the paired closer muscles are undifferentiated, the banding pattern reveals the presence of proteins common to both fiber types including myosin, actin, and tropomysin but the conspicuous absence of all unique fast fiber proteins as well as one unique slow fiber protein. By the juvenile 10th stage most of these unique proteins are present except for one unique slow fiber protein. Thus lobster fast and slow fiber differentiation entails coordinate gene activation to add unique contractile proteins.     

Distinction of fast fibers and slow fibers in frog abdominal muscle using certain choline esters]

We have registered the contractions of the frog's abdominal muscle in Ringer's solution. The contractions were produced either by acetylcholin or by succinyldicholin. The graphics showed that the succinyldicholin contractions were much slower than the acetylcholin ones. The tracings were not equalized by a preliminary addition of eserin. We conclude that acetylcholine excites the fast fibers and that succinyldicholin excites the slow fibers of the muscle.     

Substrate and enzyme profile of fast and slow skeletal muscle fibers in rhesus monkeys

Results from the Russian Cosmos program suggest that the rhesusmonkey is an excellent model for studying weightlessness-induced changes in muscle function. Consequently, the purpose of this investigation was to establish the resting levels of selected substrateand enzymes in individual slow- and fast-twitch muscle fibers of therhesus monkey. A second objective was to determine the effect of an18-day sit in the Spacelab experiment-support primate facility[Experimental System for the Orbiting Primate (ESOP)].Muscle biopsies of the soleus and medial gastrocnemius muscles wereobtained 1 mo before and immediately after an 18-day ESOP sit. Thebiopsies were freeze-dried, and individual fibers were isolated andassayed for the substrates glycogen and lactate and for the high-energyphosphates ATP and phosphocreatine. Fiber enzyme activity was alsodetermined for the glycolytic enzymes phosphofructokinase and lactatedehydrogenase (LDH) and for the oxidative markers 3-hydroxyacyl-CoAdehydrogenase (-OAC) and citrate synthase. Consistent with otherspecies, the fast type II fibers contained higher glycogen content thandid the slow type I fibers. The ESOP sit had no significant effects onthe metabolic profile of the slow fibers of either muscle or the fast fibers of the soleus. However, the fast gastrocnemius fibers showed asignificant decline in phosphocreatine and an increase in lactate. Also, similar to other species, the fast fibers contained significantly higher LDH activities and lower 3-hydroxyacyl-CoA dehydrogenase activities. For the muscle enzymes, the quantitatively most important effect of the ESOP sit occurred with LDH where activities increased inall fiber types postsit except the slow type I fiber of the medial gastrocnemius.

     

Estimation of the interplay between groups of fast and slow muscle fibers of the tibialis anterior and gastrocnemius muscle while running.

Electromyograms recorded from the lower limbs of humans while running were submitted to a time/frequency analysis using wavelets. The results of the wavelet analysis yielded intensity spectra at every time point during the swing and the stance phase. It was previously shown that more or less high frequency components get activated during different periods of the movement. The purpose of this study was to test to what extent the spectra can be reconstructed by a linear superposition of two generating spectra that were associated to groups of fast and slow muscle fibers. The terms fast and slow do not only refer to the conduction velocity but also to the shape of the motor unit action potential and are used to characterize the groups in a broader sense. The principal component analysis of the spectra confirmed that a two dimensional spectral space was appropriate. A parametric spectral decomposition was used to extract the generating spectra within the two dimensional spectral space. The generating spectra were in turn used to compute the power with which the groups of muscle fibers contribute to the measured spectra and thus to the overall muscular activity. The power that was obtained for the different time points during the movement reflects the biomechanically important interplay between the groups of muscle fibers while running.     

Effects of pH on contraction of rabbit fast and slow skeletal muscle fibers.

We have investigated (a) effects of varying proton concentration on force and shortening velocity of glycerinated muscle fibers, (b) differences between these effects on fibers from psoas (fast) and soleus (slow) muscles, possibly due to differences in the actomyosin ATPase kinetic cycles, and (c) whether changes in intracellular pH explain altered contractility typically associated with prolonged excitation of fast, glycolytic muscle. The pH range was chosen to cover the physiological pH range (6.0-7.5) as well as pH 8.0, which has often been used for in vitro measurements of myosin ATPase activity. Steady-state isometric force increased monotonically (by about threefold) as pH was increased from pH 6.0; force in soleus (slow) fibers was less affected by pH than in psoas (fast) fibers. For both fiber types, the velocity of unloaded shortening was maximum near resting intracellular pH in vivo and was decreased at acid pH (by about one-half). At pH 6.0, force increased when the pH buffer concentration was decreased from 100 mM, as predicted by inadequate pH buffering and pH heterogeneity in the fiber. This heterogeneity was modeled by net proton consumption within the fiber, due to production by the actomyosin ATPase coupled to consumption by the creatine kinase reaction, with replenishment by diffusion of protons in equilibrium with a mobile buffer. Lactate anion had little mechanical effect. Inorganic phosphate (15 mM total) had an additive effect of depressing force that was similar at pH 7.1 and 6.0. By directly affecting the actomyosin interaction, decreased pH is at least partly responsible for the observed decreases in force and velocity in stimulated muscle with sufficient glycolytic capacity to decrease pH.     

Identification of sarcolemma-associated antigens with differential distributions on fast and slow skeletal muscle fibers

We have identified three sarcolemma-associated antigens, including two antigens that are differentially distributed on skeletal muscle fibers of the fast, fast/slow, and slow types. Monoclonal antibodies were prepared using partially purified membranes of adult chicken skeletal muscles as immunogens and were used to characterize three antigens associated with the sarcolemma of muscle fibers. Immunofluorescence staining of cryosections of adult and embryonic chicken muscles showed that two of the three antigens differed in expression by fibers depending on developmental age and whether the fibers were of the fast, fast/slow, or slow type. Fiber type was assigned by determining the content of fast and slow myosin heavy chain. MSA-55 was expressed equally by fibers of all types. In contrast, MSA-slow and MSA-140 differed in their expression by muscle fibers depending on fiber type. MSA-slow was detected exclusively at the periphery of fast/slow and slow fibers, but was not detected on fast fibers. MSA-140 was detected on all fibers but fast/slow and slow fibers stained more intensely suggesting that these fiber types contain more MSA-140 than fast fibers. These sarcolemma-associated antigens were developmentally regulated in ovo and in vitro. MSA-55 and MSA-140 were detected on all primary muscle fibers by day 8 in ovo of embryonic development, whereas MSA-slow was first detected on muscle fibers just before hatching. Those antigens expressed by fast fibers (MSA-55 and MSA-140) were expressed only after myoblasts differentiated into myotubes, but were not expressed by fibroblasts in cell culture. Each antigen was also detected in one or more nonskeletal muscle cell types: MSA-55 and MSA-slow in cardiac myocytes and smooth muscle of gizzard (but not vascular structures) and MSA-140 in cardiac myocytes and smooth muscle of vascular structures. MSA-55 was identified as an Mr 55,000, nonglycosylated, detergent-soluble protein, and MSA-140 was an Mr 140,000, cell surface protein. The Mr of MSA-slow could not be determined by immunoblotting or immunoprecipitation techniques. These findings indicate that muscle fibers of different physiological function differ in the components associated with the sarcolemma. While the function of these sarcolemma-associated antigens is unknown, their regulated appearance during development in ovo and as myoblasts differentiate in culture suggests that they may be important in the formation, maturation, and function of fast, fast/slow, and slow muscle fibers.     

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.     

Highly homologous filamin polypeptides have different distributions in avian slow and fast muscle fibers

The high molecular weight actin-binding protein filamin is located at the periphery of the Z disk in the fast adult chicken pectoral muscle (Gomer, R. H., and E. Lazarides, 1981, Cell, 23: 524-532). In contrast, we have found that in the slow anterior latissimus dorsi (ALD) muscle, filamin was additionally located throughout the l band as judged by immunofluorescence with affinity-purified antibodies on myofibrils and cryosections. The Z line proteins desmin and alpha-actinin, however, had the same distribution in ALD as they do in pectoral muscle. Quantitation of filamin and actin from the two muscle types showed that there was approximately 10 times as much filamin per actin in ALD myofibrils as in pectoral myofibrils. Filamin immunoprecipitated from ALD had an electrophoretic mobility in SDS polyacrylamide gels identical to that of pectoral myofibril filamin and slightly greater than that of chicken gizzard filamin. Two-dimensional peptide maps of filamin immunoprecipitated and labeled with 125I showed that ALD myofibril filamin was virtually identical to pectoral myofibril filamin and was distinct from chicken gizzard filamin.     

Endothermic force generation in fast and slow mammalian (rabbit) muscle fibers.

Isometric tension responses to rapid temperature jumps (T-jumps) of 3-7 degrees C were examined in single skinned fibers isolated from rabbit psoas (fast) and soleus (slow) muscles. T-jumps were induced by an infrared laser pulse (wavelength 1.32 microns, pulse duration 0.2 ms) obtained from a Nd-YAG laser, which heated the fiber and bathing buffer solution in a 50-microliter trough. After a T-jump, the temperature near the fiber remained constant for approximately 0.5 s, and the temperature could be clamped for longer periods by means of Peltier units assembled on the back trough wall. A T-jump produced a step decrease in tension in both fast and slow muscle fibers in rigor, indicating thermal expansion. In maximally Ca-activated (pCa approximately 4) fibers, the increase of steady tension with heating (3-35 degrees C) was approximately sigmoidal, and a T-jump at any temperature induced a more complex tension transient than in rigor fibers. An initial (small amplitude) step decrease in tension followed by a rapid recovery (tau(1); see Davis and Harrington, 1993) was seen in some records from both fiber types, which presumably was an indirect consequence of thermal expansion. The net rise in tension after a T-jump was biexponential, and its time course was characteristically different in the two fibers. At approximately 12 degrees C the reciprocal time constants for the two exponential components (tau(2) and tau(3), respectively, were approximately 70.s(-1) and approximately 15.s(-1) in fast fibers and approximately 20.s(-1) and approximately 3.s(-1) in slow fibers. In both fibers, tau(2) ("endothermic force regeneration") became faster with an increase in temperature. Furthermore, tau(3) was temperature sensitive in slow fibers but not in fast fibers. The results are compared and contrasted with previous findings from T-jump experiments on fast fibers. It is observed that the fast/slow fiber difference in the rate of endothermic force generation (three- to fourfold) is considerably smaller than the reported differences in the "phosphate release steps" (> 30-fold).