Influence of ionic composition, buffering agent, and pH on the histochemical demonstration of myofibrillar actomyosin ATPase

Menthol nanoliposomes enhanced anti-tumor immunotherapy by increasing lymph node homing of dendritic cell vaccines

Menthol, a cyclic terpene alcohol, plays a critical role in overcoming the blood-brain barrier and stratum corneum barrier. Herein, we innovatively propose a menthol nanoliposome (Men-nanoLips) that can dramatically increase lymph node accumulation of the dendritic cell (DC)-based anti-tumor vaccines. Specifically, Men-nanoLips efficiently enhanced lymphatic endothelial cell (EC) barrier permeability by reducing the expression of tight junction proteins. And interestingly, Men-nanoLips not only up-regulated the expression of CCR7 in DCs but also increased the secretion of CCL21 in lymphatic ECs. Moreover, Men-nanoLips promoted DC vaccine maturation as evidenced by increasing the expression of costimulatory molecules and up-regulating the pseudopodia-like protein. With those complementary mechanisms provided by Men-nanoLips, the number of the B16 whole-tumor cell lysate-loaded DCs that target the draining LN enhanced remarkably and significantly boosted the treatment efficacy of DC anti-tumor vaccines. Therefore, we concluded that Men-nanoLips could be instructive for increasing LN homing of DC vaccines.

Immunohistochemical fiber typing of harbor seal skeletal muscle

There is strong evidence that pinnipeds maintain a lipid-based, aerobic metabolism during diving. However, the few fiber-typing studies performed on pinniped skeletal muscles are not consistent with an aerobic physiological profile. The objective of this study was to reexamine the fiber type distribution throughout the primary locomotory muscles of the harbor seal Phoca vitulina. Results from immunohistochemical (IHC) fiber typing indicated that harbor seal swimming muscles (the epaxial muscles) are composed of 47.4% type I (slow twitch, oxidative) fibers and 52.8% IIa (fast twitch,oxidative) fibers, which are homogeneously distributed throughout the muscle. Harbor seal pectoralis, a secondary swimming muscle, was composed of 16.2%type I and 84.3% type IIa fibers. No fast twitch, glycolytic (type IIb) fibers were detected in either muscle, in contrast to published data on fiber typing of harbor seal epaxial muscles using traditional histochemical techniques. The extreme specificity inherent in the IHC fiber typing procedure leads us to conclude that harbor seal swimming muscle is entirely composed of oxidative fibers. Our results are consistent with the enzymatic analyses of pinniped skeletal muscle that support the use of lipid-derived aerobic catabolism to fuel working muscle during diving in these marine mammals.

Postmortem alterations in the pH range of myofibrillar ATPase activation/inactivation

A histochemical assay for myofibrillar adenosine triphosphatase (mATPase) activity is routinely utilized in the delineation of fiber types in healthy human skeletal muscle. Each fiber type has a specific pH range of mATPase stability (activation). Outside of this pH range, mATPase activity is labile (inactivated), no reaction product is formed, and the fibers remain unstained. The aim of the present study was to carefully investigate the pH stability/lability of mATPase in postmortem muscles. To this end, vastus lateralis muscle samples were obtained approximately 0.5, 1, 2, 3, and 4 days after death, as well as control samples from a healthy young man and woman. Serial cross sections of the muscle samples were assayed for mATPase activity throughout preincubation pH ranges of 4.15-4.7 and 10.2-10.5 in increments of 0.05 pH units. Myosin heavy chain analysis (as well as a regression analysis comparing fiber type area and relative myosin heavy chain content) verified the mATPase-based fiber types. The pH ranges of mATPase stability/lability for the control samples were as previously reported, and support the use of preincubation pH values of 4.3, 4.6, and 10.4 for the delineation of fiber types in normal human muscle. For the postmortem samples, both quantitative and qualitative changes altered the pH ranges of mATPase activation/inactivation. Quantitative changes consisted of a time-dependent loss of mATPase activity that was inhibited in all fibers outside the pH range of 4.15-10.50. In addition, qualitative changes caused "shifts to the left" in mATPase stability within the fast fiber types (IIA and IIB). As such, complete inhibition of mATPase activity did not occur until preincubation at pH 4.45 and pH 4.30 for fiber types IIA and IIB, respectively. For the postmortem vastus lateralis muscle samples, optimal preincubation pH values for mATPase-based fiber type delineation were pH 4.30, 4.45, and 10.35. The reason for these qualitative changes in mATPase stability is not known. However, postmortem changes such as increased lactate production and marked acidification may play a role.

Properties of sprouted rat motor units: effects of period of enlargement and activity level

The effects of short and prolonged partial denervation of lateral gastrocnemius muscles in sedentary and active rats (running) were examined. In PD muscles of sedentary animals the mean motor unit (MU) tetanic force after 30 days was not different than that measured after 90 days. Increased locomotor activity over the same period (voluntary running, approximately equal to 6 km/day) resulted in an increase in mean MU tetanic force of enlarged MUs (28%). The absence of a significant increase in mean muscle fiber area suggested an activity-related enhancement of motoneuron sprouting. However, the small magnitude of this increase, relative to the potential for further sprouting, indicates the activity effect is not strong and may be partly due to fiber area changes not evident with whole muscle analysis. Nonetheless, these data demonstrate that daily locomotor activity can enhance the tension-generating capacity of chronically enlarged MUs.

Myosin isoforms and muscle fiber characteristics in equine gluteus medius muscle

BACKGROUND

To date, four different myosin heavy chain (MyHC) isoforms have been identified in adult skeletal muscle of a number of species: types I, IIa, IIx or IId, and IIb. The aim of this study was to investigate the distribution of various MyHC isoforms in the equine gluteus medius and gluteus profundus muscles in relation with several morphometric variables of muscle fibers.

METHODS

Samples from different depths of the gluteus medius muscle (2, 4, 6, and 8 cm) and gluteus profundus muscle of five sedentary horses were examined by MyHC gel electrophoresis, monoclonal antibodies staining against fast, slow and neonatal MyHC isoforms, myosin adenosine triphosphatase (m-ATPase) activity, nicotinamide adenine dinucleotide tetrazolium reductase, alpha-glycerophosphate dehydrogenase, and alpha-amylase-PAS. Data about relative frequencies, sizes, and capillaries of the various histochemical fiber types were collected by morphometry.

RESULTS

Three MyHC isoforms were present in the gluteus medius muscle. Two of them comigrated with type I and IIa MyHC isoforms of rat diaphragm (used as a control). The third isoform showed an electrophoretic mobility closer to type IIx than to the IIb MyHC isoform of rat diaphragm. Only two MyHC isoforms (type I and IIa) were detected in the gluteus profundus muscle. In both muscles, type I fibers (high m-ATPase activity at pH 4.5) only reacted with the anti slow-MyHC antibody and both type IIA and IIB fibers (low and moderate m-ATPase activity at pH 4.5, respectively) only reacted with the anti fast-MyHC antibody. No cross-reactivity of fibers positive for both antibodies was found except for the scarce type IIC fibers. Fiber types and capillaries were heterogeneously distributed across the gluteus medius muscle. The deeper regions of this muscle were found to contain a higher percentage of type I fibers, a large number of capillaries and a lower proportion of type IIB fibers compared to the superficial regions of the muscle. The gluteus profundus muscle had more abundant and larger type I fibers than the deepest sampling site of the gluteus medius muscle.

CONCLUSIONS

These results show the existence of three different MyHC isoforms in the equine gluteus medius muscle and that fiber types and MyHC isoforms are heterogeneously distributed within this muscle. The distribution of slow-twitch and fast-twitch MyHCs among the fibers determined by immunohistochemistry was in agreement with histochemically identified type I and type II fibers, respectively.

Four forearm flexor muscles of the horse, Equus caballus: anatomy and histochemistry

Two of the forearm flexors of the horse, the superficial and deep digital flexor muscles, are critical to support the digital and fetlock joints, exhibit differing insertions, and are passively supported by the proximal and distal check ligaments, respectively. These two muscles differ in histochemical composition and architecture. The differences are correlated with the different stress levels transmitted through their tendons, and the different frequencies of clinical breakdown that have been reported. Both muscles contain type I and type IIa fibers. A few type IIb fibers occurred in the deep digital flexor. The superficial digital flexor contained approximately 56% type I fibers, extremely short muscle fibers, and extensive connective tissue investment. In contrast, the deep digital flexor had three muscle heads: ulnar, radial, and "long" and "short" regions of the humeral head. The "long" and "short" regions of the humeral head contained 33% and 44% type I fibers, respectively, fiber lengths three to four times as long as those in the superficial digital flexor, and relatively less connective tissue investment. Flexor carpi radialis and flexor carpi ulnaris compared most closely with the humeral head of the deep digital flexor. These data suggest a correlation of the unique architecture of superficial digital flexor with its proposed elastic storage properties during locomotion in horses, and an explanation for the frequent breakdown of the superficial digital flexor in athletic horses.

How unequivocal is the muscle fibre type concept?

Different histochemical identification methods for muscle fibre types have been introduced over the years. Most of them have been based on myosin ATPase activity after different kinds of preincubations, alone or in combination with oxidative enzymes. Comparative studies have shown, however, that the different methods result in nonidentical subgroups of type II fibres. Optical density values of individual fibres after incubation of serial sections for alkali- or copper-preincubated ATPase, NADH-TR, and fibre diameter, combined in two-dimensional plots, have for a long time been used in our laboratory to separate three subgroups of type II fibres. A cluster analysis, based on the data mentioned above, results in three subgroups of type II fibres in rat plantaris muscle. In comparison, earlier studies comparing different histochemical methods and reporting lack of correspondence between them have been based on two subgroups of type II fibres only. It is suggested that part of the lack of correspondence is due to unequal and incomplete separation by the methods used in the comparative studies, and that the three subgroups of type II fibres identified in the cluster analysis are type IIA, IIX and IIB, respectively. The need for a consensus on a common basis for histochemical identification of muscle fibre types is emphasized.

Favourable associations between the myosin heavy-chain and light-chain isoforms in human skeletal muscle

Histochemical and biochemical analyses were performed in order to examine the relationship between myosin light-chain (LC) isoforms and fibre-type distributions in whole human skeletal muscle. Muscle biopsies were obtained from the vastus lateralis muscle in six healthy men, and analysed for the relative area occupied by each fibre type (percentage of fibre type area) and the molar ratio of each LC isoform. The percentage of type I fibre area was positively correlated with the molar ratio of slow LC (LC1s and LC2s) to total LC. The regression line was located below the line of unity. Also, the ratio of percentage of type IIa fibre area to that of type II fibre area was positively correlated with the molar ratio of the fast alkali LC LC1f to fast alkali LCs LC1f and LC3f. These results support previous study, having shown that in human skeletal muscle some type I fibres express various amounts of fast LC in addition to slow LC and suggest that fast myosin heavy-chain HCIIa is favourably associated with LC1f, whereas HCIIb is favourably associated with LC3f.

To what extent is hindlimb suspension a model of disuse?

The extent to which the remaining active or passive components of muscle mechanical stress not associated with weightbearing are involved in preserving muscle morphological and functional characteristics in the rodent hindlimb suspension model is not known. Such information would be relevant to the construction of appropriate countermeasures for the disuse atrophy associated with muscle unloading. This question was addressed by superimposing 2 weeks of hindlimb suspension and neuromuscular quiescence, achieved by the chronic neural application of the sodium channel blocker tetrodotoxin. A major portion of the muscle size characteristics of the fast anti-gravity gastrocnemius and plantaris, and the functional characteristics of the plantaris, were maintained by the full range voluntary activity remaining after suspension. Muscle mass of the slow soleus was compromised regardless of this residual activity. Indeed, for fast ankle extensors, hindlimb unloading resembles more closely a model of normal usage than of disuse, but for slow extensors this condition appears to be extremely detrimental.

Distribution of microspheres in plantaris muscles of resting and exercising rats as a function of fiber type

The purpose of this study was to determine histologically the distribution of microspheres (MSs) (14 micron), and hence the relative distribution of blood flow, in rat plantaris muscle relative to the fiber types (fast-twitch-oxidative-glycolytic [FOG], fast-twitch-glycolytic [FG], and slow-twitch-oxidative [SO]). Three conditions were investigated: 1) preexercise standing; 2) treadmill locomotion at 15 m/min (fast walking); and 3) treadmill locomotion at 60 m/min (moderate galloping). The MS suspension (containing 1 x 10(6) MSs) was infused into the ascending aorta via a catheter in the carotid artery under each of the 3 conditions so that MSs were distributed to the tissues in proportion to their respective blood flows. Sections (20 micron) of the plantaris muscle were cut and assayed for reduced nicotinamide adenine dinucleotide tetrazolium reductase (NADH-TR) and myofibrillar adenosine triphosphatase (ATPase) activities so the fibers could be typed as SO, FOG, or FG. MSs were located in the NADH-TR sections, and the fibers next to the MSs were classified and counted. The observed numbers of fibers of each type in each condition that were adjacent to MSs were compared to the predicted number of adjacent fibers based on the assumption the MSs were randomly distributed in the tissue. This analysis demonstrated that MSs (and blood flows) were preferentially distributed to SO fibers during preexercise, to SO and FOG fibers during slow locomotion, and to FOG fibers during fast locomotion. The data support the contention that blood flow is distributed in muscles of conscious animals as functions of fiber type and exercise intensity.

Determination of fiber types of chicken skeletal muscles based on reaction for actomyosin, calcium+2, magnesium+2-dependent adenosine triphosphatase

Muscle fiber subtypes, determined with the actomyosin Ca+2,Mg+2-adenosine triphosphatase (ATPase) reaction in chicken anterior latissimus dorsi and posterior latissimus dorsi muscles, were demonstrated only after acid or alkaline preincubation followed by a 60-min enzyme incubation. In contrast, subtypes were demonstrated in the sartorius muscle either with or without preincubation. A single-step procedure was therefore possible with this muscle. The results were generally similar to those obtained previously with the mycosin Ca+2-ATPase procedure. Both methods revealed corresponding muscle fiber subtypes, with the exceptions noted below. The actomyosin Ca+2,Mg+2-ATPase procedure, following preincubation at pH 9.4 and 10.3, resulted in a similar reaction intensity in all fiber types. With the myosin Ca+2-ATPase procedure, the IRA (slow) type in anterior latissimus dorsi and sartorius muscles and the I (slow), IIR (fast oxidative-glycolytic), and IIW (fast glycolytic) types in posterior latissimus dorsi muscle had a higher reaction intensity following preincubation at pH 9.4 than at pH 10.3. Fiber Types IIR and IIW in sartorius muscle were easily distinguished with the actomyosin Ca+2,Mg+2-ATPase procedure.

Conversion of rat muscle fiber types. A time course study

Rats were used in this study to determine the time course of conversion of muscle fiber types. The right or left gastrocnemius muscle was removed thereby causing an overload on the ipsilateral soleus and plantaris muscles. The contralateral limb served as a control. The type II to type I fiber conversion was followed histochemically in the soleus and plantaris muscles for one to six weeks following surgery. Muscle sections were stained for myofibrillar actomyosin ATPase and NADH tetrazolium reductase. The type I population in the soleus muscle was 99.3% six weeks after synergist removal. The plantaris muscle underwent a two fold increase in the percentage of type I fibers after six weeks. Transitional fibers were prominent in the plantaris muscle and reached their peak at 4% (P less than 0.05) of the total population, four weeks after surgery.

Comparison of fiber types in skeletal muscles from ten animal species based on sensitivity of the myofibrillar actomyosin ATPase to acid or copper

Comparisons were made of the histochemical characteristics of skeletal muscle from 10 animal species. The basic comparison was made from the staining patterns for the myofibrillar actomyosin ATPase produced by preincubation of fresh frozen cross-sections of muscle at alkaline pH (10.30) or acid pH (4.60) with those produced by preincubation in media containing Cu2+ at alkaline pH (10.30), near neutral pH (7.40), or acid pH (4.60). Muscle sections were also stained for reduced nicotinamide adenine dinucleotide tetrazolium reductase and alpha-glycerophosphate dehydrogenase to provide an indication of the relative oxidative and glycolytic capacity of the different fiber types. Type II fibers in mixed fibered muscles were either very sensitive, moderately sensitive, or relatively insensitive to inactivation of the myofibrillar actomyosin ATPase after acid preincubation. These fibers were identified as type IIA1, IIA2, and IIA3, respectively. The myofibrillar actomyosin ATPase of the type I fibers of these muscles, with the exception of those in mouse muscle, was activated by pretreatment with acid. A separation of animal species was possible based on the stability of the IIA1 fibers to inclusion of Cu2+ in the preincubation medium. For one group of animals (rat, mouse, monkey, man, dog, rabbit, and cow), a reciprocal relationship existed between lability to acid and stability to Cu2+ for type IIA1 and IIA3 fibers, respectively. For the second group of animals (horse, ass, and cat) there was a parallel relationship between lability or stability of the type IIA1 and IIA3 fibers to pretreatment with either acid or Cu2+.

Identification of fiber types in rat skeletal muscle based on the sensitivity of myofibrillar actomyosin ATPase to copper

Experiments are reported demonstrating that differential rates of inactivation of the histochemical staining for myofibrillar actomyosin ATPase in rat skeletal muscle fibers exist following inclusion of low concentrations of Cu2+ in the preincubation medium. This response of rat muscle occurs at near neutral (7.40), acid (4.60), and alkaline (10.30) pH. The response to Cu2+ appears to result from a binding of Cu2+ onto the myofibrillar complex, probably on myosin itself, as it can be reversed by soaking of the pretreated muscle sections in sodium cyanide or the Cu2+ chelator diethyldithiocarbamate. The pattern of modification of the staining pattern following pretreatment with Cu2+ is the mirror image of that produced by pretreatment with acid. The results demonstrate that the inclusion of Cu2+ in the preincubation media for the myofibrillar actomyosin ATPase can be a useful tool to differentiate fiber types. They also support the earlier conclusion that three distinct types of type II fibers can be identified in rat skeletal muscle based on the histochemical staining for myofibrillar actomyosin ATPase.