Muscle capillaries in tenotomized human muscles

The capillaries were studied in tenotonized human muscles after tenotomy or spontaneous rupture of the tendon. The mean capillary area was not significantly different in the patients with tenotomy, or with spontaneous rupture of the tendon, as compared to intact muscles. The mean basement membrane area as a percentage of total capillary area was significantly larger and the size capillary lumen significantly smaller in the injured than in the intact muscles. The alterations of the capillaries were time-dependent.     

New type of snRNP containing nuclear bodies in plant cells

In larch (Larix decidua Mill.) microspores a new type of nuclear bodies has been found which are an element of the spatial organization of the splicing system in plant cell. These are bizonal bodies, ultrastructurally differentiated into a coiled part and a dense part. Using immunocytochemistry and in situ hybridization at the EM level, the coiled part of the bizonal body was found to contain snRNA including U2 snRNA, Sm proteins and nucleolar proteins of the agyrophilic type and fibrillarin. The dense part contains Sm proteins but lacks snRNA. Such a separation of macromolecules related to splicing occurring within the bizonal bodies microspore is striking by the similarity of these bodies to amphibian oocyte snurposomes. The occurrence in plant cells, beside widely known coiled bodies (CBs), also of other nuclear bodies related to splicing proves that in plants similarly as for animals the differentiation among domains containing elements of the splicing system occurs.     

Histochemical heterogeneity of intrafusal muscle fibres in slow and fast skeletal muscles of the rat

Summary Intrafusal muscle fibres of the slow soleus (Sol) and fast vastus lateralis (VL) muscles of the rat were studied histochemically. Serial transverse sections were incubated for the localization of succinate dehydrogenase (SDH), alpha glycerophosphate dehydrogenase (GPD) and adenosine triphosphatase (ATPase). The latter was examined further after preincubation in acidic solution held at either low or room temperature (R_T). The bag₂ intrafusal fibres in both muscles displayed high regular and acid stable ATPase, but low SDH and GPD activities. Bag₁ intrafusal fibres showed low to moderate regular ATPase, a regional heterogeneity after R_T acid preincubation (low activity in juxtaequatorial and high in polar zones), moderate SDH, but low GPD reactions. In both muscles the chain fibres usually exhibited high ATPase for both regular and cold acid preincubated reactions, but usually low activity after R_T acid preincubation; they had high SDH but variable GPD activities. In Sol muscle, however, approximately 25% of spindles contained chain fibres that showed high acid-stable ATPase reaction after both cold and R_T acid preincubation. In contrast, chain fibres in some VL spindles had a characteristically low ATPase reaction even after cold acid preincubation. This study, therefore, has delineated the existence of an inherent heterogeneity among chain fibres (with respect to their histochemical reactions) in muscle spindles located within slow and fast muscles and also between those found within populations of either Sol or VL muscle spindles.     

Colocalization of neuropeptides and NADPH-diaphorase in the intra-adrenal neuronal cell bodies and fibres of the rat

Colocalization of vasoactive intestinal peptide, neuropeptide Y, calcitonin gene-related peptide, substance P, and tyrosine hydroxylase, respectively, with NADPH-diaphorase staining in rat adrenal gland was investigated using the double labelling technique. All vasoactive intestinal peptide- and some neuropeptide Y-immunoreactive intrinsic neuronal cell bodies seen in the gland were double stained with NADPH-diaphorase. Double labelling also occurred in some nerve fibres immunoreactive to vasoactive intestinal peptide and neuropeptide Y in the medulla and cortex. No colocalization of calcitonin gene-related peptide, substance P or tyrosine hydroxylase immunoreactivity with NADPH-diaphorase staining was observed. However, nerve fibres with varicosities immunoreactive for all the neuropeptides examined were closely associated with some of the NADPH-diaphorase-stained neuronal cell bodies. Thus, in rat adrenal gland, nitric oxide is synthesized in all ganglion cells containing vasoactive intestinal peptide and in some containing neuropeptide Y, but not in those containing calcitonin gene-related peptide, substance P or tyrosine hydroxylase.     

Histoenzymatic characterization of sub-types of type I fibres in fast muscles of rats.

The histochemical activities of succinic dehydrogenase (SDH), myofibrillar Adenosine triphosphatase (ATPase) and alpha glycerophosphate dehydrogenase were studied in serial sections of rat vastus lateralis (red) (RVL), gastrocnemius and diaphragm muscles. Three main fibre-types were distinguished. The "Type I" fibres of RVL and gastrocnemius muscles fell into two distinct groups: one category--"Type IA" showed very low ATPase activity. The second category of "Type IB" fibres displayed moderate ATPase reaction. The "Type IA" fibres were divisible into two sub-groups when tested for SDH reaction. "Type IA1" fibres possessed a homogenous distribution of diformazan granules throughout the fibre: "Type IA2" fibres displayed characteristic "moth-eaten" pattern of diformazan localization. The diaphragm muscle did not show either "Type IB" or "Type IA2" varieties. The great majority of TypeI fibres were sub-type IA1 in the three fast muscles studied. It is also demonstrated here that an inherent heterogeneity exists between Type I filores of diaphragm and leg muscles in regard to alpha-GPD localization. This histochemical data emphasizes the fact that subdivision of TypeI striated muscle fibres of mammalian animals into two sub-types is only approximate and that a further subcategorization is possible.     

Type IIC fibres in certain muscles of the adult rat (sedentary and exercised)

Samples were taken, at fixed levels, of the vastus lateralis, the caput lateralis of the gastrocnemius muscle and the longissimus lumbaris of 72 Wistar rats which were either sedentary or subjected to various exercise schedules. The samples were analyzed using the histochemical technique of myosin ATPase (m-ATPase) after preincubation at pH 4.2, and the fibre-types I, II (IIA and IIB) and IIC were identified, calculating the percentage of type IIC fibres as well as their minimum diameter. The percentages of these IIC fibres found in the red and mixed parts of the gastrocnemius (caput lateralis) and the longissimus lumbaris were between 0.7% and 2.6%. However, their presence was not detected in the vastus lateralis or in the white part of the gastrocnemius (caput lateralis). The lack of differences in this fibre type between the males and females of the population was shown statistically. Likewise, no significant modification of the IIC fibres between sedentary and exercised animals was seen. With regard to fibrillar size, females showed a smaller minimum diameter than males, the results showing a small increase in the size of these fibres in both sexes after exercise, although in most cases this was not statistically significant.     

Fiber type and metabolic dependence of T2 increases in stimulated rat muscles.

This study examined the relationships between muscle fiber type, metabolism, and blood flow vs. the increase in skeletal muscle (1)H-NMR transverse relaxation time (T2) after stimulation. Triceps surae muscles of anesthetized rats were stimulated in situ at 1-10 Hz for 6 min, and T2 was calculated from (1)H-NMR images acquired at 4.7 T immediately after stimulation. At low-to-intermediate frequencies (1-5 Hz), the stimulation-induced T2 increase was greater in the superficial, fast-twitch white portion of the gastrocnemius muscle compared with the deeper, more aerobic muscles of the triceps surae group. Although whole triceps muscle area changed in parallel with T2 after stimulation when blood flow was intact, clamping of the femoral artery during stimulation prevented an increase in muscle area but not an increase in T2. Partial inhibition of lactic acid production with iodoacetate diminished intracellular acidification (measured by (31)P-NMR spectroscopy) during brief (1.5 min) stimulation but had no significant effect either on estimated osmolite accumulation or on muscle T2 after stimulation. Depletion of muscle phosphocreatine content by feeding rats beta-guanidinopropionate decreased both estimated osmolite accumulation and T2 after 1.5-min stimulation. The results are consistent with the hypothesis that the T2 increase in stimulated muscle is related to osmotically driven shifts of fluid into an intracellular compartment.     

Responses of muscle spindles of tenotomized and hypertrophied muscles to stretching and vibration

Responses of muscle spindles of tenotomized and hypertrophied muscles to stretching and vibration were investigated. During constant stretching of the muscles with a load of 100 g the spontaneous activity of the primary endings in the control muscle was 17±1.5 spikes/sec, in the hypertrophied muscle it was unchanged, and after tenotomy it was increased to 26±1.5 spikes/sec. The discharge frequency of the secondary endings was unchanged under these circumstances. Responses of primary and secondary endings of spindles of the tenotomized muscle during the dynamic and static phases of stretching were higher in frequency than responses of spindles of normal muscles. The discharge frequency of the primary endings in the hypertrophied muscle also was increased during both phases of stretching. Responses of secondary endings of the spindles of the hypertrophied muscle were indistinguishable under these circumstances from responses of normal muscles. Primary endings of spindles of tenotomized and hypertrophied muscles, just as normally, reproduced frequencies of vibration stimulation up to 2000 Hz, but some increase in the discharge frequency was observed in the secondary endings at this time.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 8, No. 3, pp. 311–317, September, 1976.     

Rostrocaudal variation of fiber type composition in rat intercostal muscles

Summary We used the histochemical stain for ATPase to compare the fiber-type composition of rat internal and external intercostal muscles from thoracic (T) segments 2–5, 8, and 11. At each level, type II fibers were more numerous than type I fibers, type II B fibers were more numerous than II A fibers, and type I fibers were more numerous in external than in internal intercostals. However, fiber type composition varied from segment to segment. For example, the proportion of type II A fibers increased in a rostrocaudal gradient in internal but not external intercostals, and type I fibers were more prevalent at rostral and caudal than at intermediate levels in both internal and external intercostals. These results provide a basis for interpreting previous physiological and molecular studies which have compared intercostal muscles from different segmental levels.     

Lactate dehydrogenase isozymes in type I,IIA and IIB fibres of rabbit skeletal muscles

Summary Lactate dehydrogenase (LDH) isozyme patterns were analysed by polyacrylamide (PAA) slab gel electrophoresis in extracts prepared from various rabbit skeletal muscles of defined fibre composition and by PAA microelectrophoresis of microdissected, histochemically typed single muscle fibres. The results obtained by electrophoresis of whole muscle extracts generally agreed with the data obtained from single fibre electrophoresis, i.e. the LDH isozyme pattern corresponded to that of the predominant fibre type. Type I Fibres from soleus and semitendinosus muscles were characterized by a unique pattern of all 5 LDH isozymes with a predominance of LDH-1, 2 and 3. The major fraction (80%) of the type II fibres from extensor digitorum longus and tibialis anterior muscles contained only LDH-5 (M₄). About 20% of the type II fibres contained in addition to LDH-5 small amounts of LDH-4 and LDH-3. The fraction of fibres containing LDH-5, LDH-4, and LDH-3 was similar (ca. 20%) in the histochemically defined IIA and IIB subpopulations In view of the fact that the major fractions of rabbit IIB fibres display low and of IIA fibres high aerobic oxidative capacities (Reichmann and Pette 1982), these data indicate that the expression of the H-subunit of LDH is not correlated with the aerobic-oxidative capacity of the fibre. It also appears not to be correlated with the presence of different myosin isoforms in IIA and IIB fibres.     

Rostrocaudal variation of fiber type composition in rat intercostal muscles.

We used the histochemical stain for ATPase to compare the fiber-type composition of rat internal and external intercostal muscles from thoracic (T) segments 2-5, 8, and 11. At each level, type II fibers were more numerous than type I fibers, type II B fibers were more numerous than II A fibers, and type I fibers were more numerous in external than in internal intercostals. However, fiber type composition varied from segment to segment. For example, the proportion of type II A fibers increased in a rostrocaudal gradient in internal but not external intercostals, and type I fibers were more prevalent at rostral and caudal than at intermediate levels in both internal and external intercostals. These results provide a basis for interpreting previous physiological and molecular studies which have compared intercostal muscles from different segmental levels.     

ATP inhibits the hypoxia response in type I cells of rat carotid bodies

Summary During hypoxia, ATP was released from type I (glomus) cells in the carotid bodies. We studied the action of ATP on the intracellular Ca(2+) concentration ([Ca(2+)](i)) of type I cells dissociated from rat carotid bodies using a Ca(2+) imaging technique. ATP did not affect the resting [Ca(2+)](i) but strongly suppressed the hypoxia-induced [Ca(2+)](i) elevations in type I cells. The order of purinoreceptor agonist potency in inhibiting the hypoxia response was 2-methylthioATP > ATP > ADP > alpha, beta-methylene ATP > UTP, implicating the involvement of P2Y(1) receptors. Simultaneous measurements of membrane potential and [Ca(2+)](i) show that ATP inhibited the hypoxia-induced Ca(2+) signal by reversing the hypoxia-triggered depolarization. However, ATP did not oppose the hypoxia-mediated inhibition of the oxygen-sensitive TASK-like K(+) background current. Neither the inhibition of the large-conductance Ca(2+)-activated K(+) (maxi-K) channels nor the removal of extracellular Na(+) could affect the inhibitory action of ATP. Under normoxic condition, ATP caused hyperpolarization and increase in cell input resistance. These results suggest that the inhibitory action of ATP is mediated via the closure of background conductance(s) other than the TASK-like K(+), maxi-K or Na(+) channels. In summary, ATP exerts strong negative feedback regulation on hypoxia signaling in rat carotid type I cells.     

Variation in the determinants of power of chemically skinned type I rat soleus muscle fibres

We explored to which extent maximal velocity of shortening (Vmax), force per cross-sectional area (specific tension, Po) and curvature of the force–velocity relationship (a/Po in the Hill equation) contribute to differences in peak power of single, chemically skinned rat type I fibres. Force–velocity relationships were determined from isotonic contractions of 94 maximally activated fibres. Peak power (±SD) was 3.50 ± 1.64 W L⁻¹. There was a tenfold range of peak power and five-, six- and fourfold ranges for Po, Vmax and a/Po, respectively. None of the differences between fibres was explicable by differences in myosin heavy or light chain composition. The inverse relationship between a/Po and Vmax suggests a similar underlying cause. Fitting the data to the Huxley (Progr Biophys Biophys Chem 7:255–318, 1957) cross-bridge model showed that the rate constant g ₂ and the sum of the rate constants (f + g ₁) co-varied, both being low in the slowest fibres. Approximately 16% of the variation in Po could be explained by variation in the proportion of attached cycling cross-bridges (f/(f + g ₁)), but the origin of most of the variance in Po remains unknown.     

Probabilistic model of the spatial distribution of muscle fibres in human muscles

An analytical model and computer simulation model for measuring fibre density in motor units of human skeletal muscles have been described. The model was developed for Gaussian distribution of the fibres in the motor unit territory. It has been shown that fibre density measurement using a triggering fibre was a biased estimate of the actual density of the fibres in the territory. The effects of varying the standard deviation of the spatial distribution on the estimate of fibre density has been investigated, and it has been shown that for high values of standard deviation a uniform distribution of the fibres in the territory was a good first order approximation.     

Subgrouping of fast twitch fibres in skeletal muscles of man

Summary Subgroups of fast twitch (FT) muscle fibres were identified by histochemical techniques on muscle samples of m. quadriceps femoris from six male and six female subjects, who had been assigned to three groups; untrained, active and well trained (endurance runners). Slow twitch (ST) and FT fibres were initially identified using the histochemical stain for myofibrillar ATPase, preincubated at pH 10.3 and 4.3. Three people, working independently, then identified the subgroups FTa and FTb on the basis of the staining intensity for only one of the following reactions: -glycerophosphate dehydrogenase, -GPD; NADH tetrazolium reductase, NADH-TR; and myofibrillar ATPase preincubated at pH 4.6, ATPase (4.6). FTa fibres were clearly distinguished from the darker staining FTb fibres using the ATPase (4.6) reaction. Differences in the staining within the FT fibres using the -GPD and NADH-TR reactions were more subtle, and differences between subject groups were evident. The percentage of FTa fibres was overestimated for the untrained and underestimated for the well trained subjects using NADH-TR. With the -GPD stain the percentage of FTa fibres was generally underestimated. When the data for all three stains were compared, only 27% of the FT fibres were placed in the same subgroups. These results demonstrate that the subgrouping of FT fibres in man is more reliable using the differences in pH sensitivity for the myofibrillar ATPase reaction compared to histochemical reactions for oxidative or glycolytic enzymes.