Water Permeability of Isolated Muscle Fibers of a Marine Crab

This report deals with the diffusional and nondiffusional water fluxes of muscle fibers of the crab, Chionoecetes bairdi. Graphical analysis of the deuterium exchange indicates that two fiber compartments exist for water. The first, comprising about 60–70% of the fiber water, probably represents the sarcoplasm which is bounded externally by the plasma membrane. The second compartment might represent intracellular organelles. The ratio between the nondiffusional and diffusional fluxes is very much larger than that found earlier for erythrocytes and for the giant axon of the squid. A ratio of such size is unlikely to be caused by unstirred layers and more accurate determinations of the water flux must include study of the influence of the complex morphology of these muscle fibers.     

The Control of the Membrane Potential of Muscle Fibers by the Sodium Pump

Frog sartorius muscles were made Na-rich by immersion in K-free sulfate Ringer's solution in the cold. The muscles were then loaded with Na²⁴ and the extracellular space cleared of radioactivity. When such Na-rich muscles were transferred to lithium sulfate Ringer's solution at 20°C, Na efflux was observed to increase with time, to reach a maximum about 15 minutes after the transfer of the muscles to Li₂SO₄, and then to decline. The decline in efflux from these muscles was proportional to ([Na]_i)⁸ over a considerable range of [Na]_i. The membrane potential of Na-rich muscles was about -48 mv in K-free sulfate Ringer's at 4°C but changed to -76 mv in the same solution at 20°C and to -98 mv in Li₂SO₄ Ringer's at 20°C. By contrast, muscles with a normal [Na]_i showed a fall in membrane potential when transferred from K-free sulfate Ringer's to Li₂SO₄ Ringer's solution. The general conclusions from this study are (a) that Na extrusion is capable of generating an electrical potential, and (b) that increases in [Na]_i lead to reversible increases in P_Na of muscle fibers.     

Desensitization of Gamma Aminobutyric Acid (GABA) Receptors in Muscle Fibers of the Crab Cancer borealis

Carcinus muscle fibers respond to γ-aminobutyric acid (GABA) with a conductance increase that subsides rather rapidly. In the larger fibers which have low input resistance the decrease may disappear within 2 min. The inhibition of the excitatory postsynaptic potentials (EPSP's) by GABA nevertheless persists as long as the drug is applied. The subsidence of the increased conductance indicates that the membrane of the inhibitory synapses has become desensitized to GABA. The persistence of inhibition of the EPSP's appears to be due to an action of the drug on the presynaptic terminals of the excitatory axons which reduces or blocks the secretory activity that releases the excitatory transmitter.     

Control of Cell Volume in Skeletal Muscle

Regulation of cell volume is a fundamental property of all animal cells and is of particular importance in skeletal muscle where exercise is associated with a wide range of cellular changes that would be expected to influence cell volume. These complex electrical, metabolic and osmotic changes, however, make rigorous study of the consequences of individual factors on muscle volume difficult despite their likely importance during exercise. Recent charge-difference modelling of cell volume distinguishes three major aspects to processes underlying cell volume control: (i) determination by intracellular impermeant solute; (ii) maintenance by metabolically dependent processes directly balancing passive solute and water fluxes that would otherwise cause cell swelling under the influence of intracellular membrane-impermeant solutes; and (iii) volume regulation often involving reversible short-term transmembrane solute transport processes correcting cell volumes towards their normal baselines in response to imposed discrete perturbations. This review covers, in turn, the main predictions from such quantitative analysis and the experimental consequences of comparable alterations in extracellular pH, lactate concentration, membrane potential and extracellular tonicity. The effects of such alterations in the extracellular environment in resting amphibian muscles are then used to reproduce the intracellular changes that occur in each case in exercising muscle. The relative contributions of these various factors to the control of cell volume in resting and exercising skeletal muscle are thus described.     

Volume and Twitch Tension Changes in Single Muscle Fibers in Hypertonic Solutions

Single muscle fibers were exposed to solutions made hypertonic (approximately 460 milliosmols/kg water) by addition of either NaCl, glycerol, urea, acetamide, ethylene glycol, or propylene glycol. The changes in either the fiber twitch tension or the volume were measured. In the case of NaCl both fiber volume and twitch tension fall rapidly to 64 and 27% of the respective initial value. These two values were maintained for the duration of the exposure. In the case of the other substances, the fiber volume and twitch tension also decreased but in these cases the effect was transient and the fibers recovered their initial volume and twitch tension. The rate of recovery in the different hypertonic media increased in the order: glycerol < urea < ethylene glycol < propylene glycol < acetamide. In the cases of the last three substances, the initial twitch value was recovered in less than 5 min and even surpassed. However, on returning to normal Ringer the fibers' ability to twitch or to develop potassium contractures was lost. The return of the fibers to normal Ringer after exposure to these hypertonic solutions causes a transient swelling of the fibers. However, when fibers were swelled by exposure to hypotonic media, they did not lose their ability to twitch on return to the normal Ringer.     

Bacteriological Survey of the Blue Crab Industry

During sanitation inspections of 46 crabmeat processing plants on the Atlantic and Gulf Coasts, 487 samples of whole crabs immediately after cooking, cooked crabs after cooling, backed or washed (or both) crab bodies and whole crab claws, as well as 1,506 retail units of finished product were collected and analyzed bacteriologically. The 1,506 retail units (1-lb [373.24-g] cans) included 518 cans of regular (special) meat, 487 cans of claw meat, and 501 cans of lump meat. Statistical analyses showed that crabmeat from plants in Mississippi, Louisiana, and Texas had higher counts in 19 of 24 cases for the four bacteriological indices than crabmeat from plants located along the Atlantic Coast and the Gulf Coast of Florida. Aerobic plate counts of retail units collected from a previous day's production were significantly higher than those collected on the day of inspection. Regular crabmeat had consistently higher aerobic plate counts than claw or lump meat. When the product was handled expeditiously under good sanitary conditions, the bacteriological results were significantly better than the results from plants operating under poor sanitary conditions. Crabmeat produced in plants operating under good sanitary conditions had the following bacteriological content: (i) coliform organisms average most-probable-number values (geometric) of less than 20 per g; (ii) no Escherichia coli; (iii) coagulase-positive staphylococci average most-probable-number values (geometric) of less than 30 per g in 93% of the plants; (iv) aerobic plate count average values (geometric) of less than 100,000 per g in 93% of the plants, with the counts from 85% of these plants below 50,000 per g.     

Bdellovibrios in Callinectus sapidus, the Blue Crab

Bdellovibrios were recovered from the gill tissue of all of 31 crabs sampled and from all samples of epibiota obtained from the ventral shell surface of 15 crabs. The results suggest that the blue crab is a reservoir for bdellovibrios. The association with crabs may be an important factor in the ecology of the bdellovibrios.     

Taste the Traditions: Crabs, Crab Cakes, and the Chesapeake Bay Blue Crab Fishery

For centuries, people in the Chesapeake Bay watershed have harvested and consumed blue crabs (Callinectes sapidus). Historically, the production of the crabs was intimately connected to the work and knowledge of commercial watermen. In recent years, declining crab populations have resulted in an increased local use of pasteurized crab meat imported from Asia and South America. Also emerging is an ecological discourse that emphasizes pollution reduction to save crabs to eat. In this article, I analyze these production and consumption changes for Chesapeake Bay blue crabs within a broad-ranging framework of cultural models and environmental anthropology. Explicit textual information increasingly suggests that the cultural model of Chesapeake blue crabs as food is one of crab cakes made (with imported crab meat) in the "local tradition" and, to a lesser degree so far, is an emerging discourse presenting blue crabs as a culinary poster child for antipollution campaigns.     

Muscle Contraction during Hyperpolarizing Currents in the Crab

Isolated muscle fibers from the motor legs of the crab Trichodactilus dilocarcinus were submitted to strong hyperpolarizing currents of varied intensities which produced tension during the current pulse. Threshold for tension was obtained with intensities of about 0.2 x 10^–5 A, changing E_m to ca. –150 mV (starting from a resting potential ofca. –80 mV). At the closure of the anodic square pulse, a second phase of tension usually appeared superimposed upon the one obtained during hyperpolarization. The first phase of tension increased with the increase of Ca⁺⁺ concentration in the bath. Sr⁺⁺ produced the same type of mechanical output as Ca⁺⁺. When added to the normal Ca⁺⁺ concentration, Ba⁺⁺ and Mn⁺⁺ in low concentrations (up to 21.5 mM) also increased the tension of this phase, but at higher concentrations they blocked both phases while Mg⁺⁺ did not alter the tension. Of all the divalent cations employed, only Sr⁺⁺ is capable of developing tension as a substitute for Ca⁺⁺ in the external media. Procaine administered in a dosage (5 x 10^–3 W/V)which would suppress the contracture due to caffeine (10 mM), did not modify the tension developed during the hyperpolarization. The preceding data indicate that the Ca⁺⁺ required for tension during hyperpolarization comes from sites which would differ from those usually postulated for tension due to depolarization in the muscle fibers of other crustaceans (American crayfish). Furthermore, the external source of Ca⁺⁺ appears to be one mainly implicated in the induction of tension due to inward current pulses.     

Incidence of Clostridium botulinum in Crabmeat from the Blue Crab

The incidence of Clostridium botulinum in fresh crabmeat of blue crab was six out of 986 samples; in pasteurized crabmeat one sample out of 1,000 contained the organism.     

Muscle Fiber Types in Crabs: Studies on Single Identified Muscle Fibers

SYNOPSIS. Based on electrophysiological and histochemical data,four types of muscle fibers (types I, II, III and IV) can beidentified in the closer of the crab Eriphia. Although characteristicsused for typing vary among the fibers of a particular type,the combination of several parameters permits an assignment.Of particular significance for typing is the myosin ATPase activityand its stability after preincubation at different pH levels.The fiber types defined for the closer muscle can also be foundin the other leg muscles of riphia. Single, electrophysiologically identified fibers of each typewere quantitatively analyzed for several key enzymes of oxidativeand glycolytic energy metabolism (GAPDH, LDH, CS, IDH, HAD).Despite the variations found, different metabolic types canbe defined. The typing derived from biochemical studies correlateswell with that obtained electrophysiologically and histochemically.The variability of the biochemical properties, however, seemsto be considerably larger. The type I fibers can be regarded as slow oxidative, the typeII and III fibers as fast oxidative glycolytic, and the typeIV fibers as fast glycolytic.     

Tension in Isolated Frog Muscle Fibers Induced by Hypertonic Solutions

The effect of hypertonic solutions on the tension of isolated twitch muscle fibers of the frog has been investigated. Increased tonicity up to about 1.7 times normal (1.7 T) caused a very small, graded, maintained tension increase. Above about 1.7 T a large, transient contracture response was superimposed on the small tension. The contracture response was graded with tonicity and reached a maximum at 2.5 T of 108 ± 25 mN·mm² a third of the maximum tetanic tension in isotonic solution. Contracture tension developed with a delay which decreased with increased tonicity. The contracture threshold was lower and the delay shorter in small fibers than in large. Contractures were obtained equally well in depolarized as in polarized fibers. They were completely suppressed by 0.1–0.5 mM tetracaine. The possible mechanism responsible for the tension-inducing effect of hypertonic solutions is discussed in terms of the close similarity between the properties of these contractures and those caused by caffeine, and it is suggested that the effect is due to a release of calcium from internal stores.     

侧足厚蟹有髓鞘神经纤维的超微结构电镜观察

侧足厚蟹(Helice latimera)的有髓鞘神经纤维直径约在5—12μm之间,髓鞘厚约2μm左右。髓鞘由内外膜层和中间微管层组成。外膜层层数约20层,排列紧密,微管层厚约0．31μm,内膜层层数约20层。轴突膜形成嵴,伸进轴腔内,在轴腔内还存在维管束和膜层束结构。在髓鞘结构中观察到两种类型的高嗜锇性区域,一种是由排列规则且明暗交替的膜层结构组成,另一种是非膜层结构组成。     

Bacterial Flora of the Hemolymph of the Blue Crab, Callinectes sapidus: Numerical Taxonomy

Bacteria isolated from the hemolymph of normal blue crabs were found to be predominantly Vibrio sp., Pseudomonas sp., Acinetobacter sp., Bacillus sp., Flavobacterium sp., and coliforms. Vibrio parahaemolyticus, a cosmopolitan facultative pathogen widely implicated in outbreaks of gastroenteritis related to the consumption of improperly processed seafood, was present in crabs collected between the months of May to November and was identified in up to 21% of the hemolymphs sampled.     

Swelling of Skinned Muscle Fibers of the Frog: Experimental Observations

Frog skeletal muscle fibers, mechanically skinned under water-saturated silicone oil, swell upon transfer to aqueous relaxing medium (60 mM KCl; 3 mM MgCl₂; 3 mM ATP; 4 mM EGTA; 20 mM Tris maleate; pH = 7.0; ionic strength 0.15 M). Their cross-sectional areas, estimated with an elliptical approximation, increase 2.32-fold (±0.54 SD). Sarcomere spacing is unaffected by this swelling. Addition of 200 mM sucrose to relaxing medium had no effect on fiber dimensions, whereas decreasing pH to 5.0 caused fibers to shrink nearly to their original (oil) size. Decreasing MgCl₂ to 0.3 mM caused fibers to swell 10%, and increasing MgCl₂ to 9 mM led to an 8% shrinkage. Increasing ionic strength to 0.29 M with KCl caused a 26% increase in cross-sectional area; decreasing ionic strength to 0.09 M had no effect. Swelling pressure was estimated with long-chain polymers, which are probably excluded from the myofilament lattice. Shrinkage in dextran T10 (number average mol wt 6,200) was transient, indicating that this polymer may penetrate into the fibers. Shrinkage in dextran T40 (number average mol wt 28,000), polyvinylpyrrolidone (PVP) K30 (number average mol wt 40,000) and dextran T70 (number average mol wt 40,300) was not transient, indicating exclusion. Maximal calcium-activated tension is decreased by 21% in PVP solutions and by 31% in dextran T40 solutions. Fibers were shrunk to their original size with 8 × 10^-2 g/cm³ PVP K30, a concentration which, from osmometric data, corresponds to an osmotic pressure (II/RT) of 10.5 mM. As discussed in the text, we consider this our best estimate of the swelling pressure. We find that increasing ionic strength to 0.39 M with KCl decreases swelling pressure slightly, whereas decreasing ionic strength to 0.09 M has no effect. We feel these data are consistent with the idea that swelling arises from the negatively charged nature of the myofilaments, from either mutual filamentary repulsion or a Donnan-osmotic mechanism.     

Genetic Heterogeneity of the Blue Swimming Crab (Portunus pelagicus) in Thailand Determined by AFLP Analysis

Genetic diversity and population differentiation of the blue swimming crab (Portunus pelagicus) in Thailand, originating from Ranong and Krabi located in the Andaman Sea (west) and Chanthaburi, Prachuap Khiri Khan, and Suratthani located in the Gulf of Thailand (east), were examined by AFLP analysis. High genetic diversity of P. pelagicus in Thai waters was found (N=72). The four primer combinations generated 227 AFLP fragments, and the percentage of polymorphic bands in each geographic sample was 66.19-94.38%. The mean genetic distance between pairs of samples was 0.1151-0.2440. Geographic heterogeneity analyses using the exact test and FST-based statistics between all pairwise comparisons were statistically significant (P<0.01), indicating a fine-scale level of intraspecific population differentiation of Thai P. pelagicus. The estimated number of migrants per generation (Nem) was 0.26-0.76, suggesting restricted gene flow levels of P. pelagicus in Thai waters.     

Electrotonic Interaction between Muscle Fibers in the Rabbit Ventricle

Transmembrane potentials were recorded simultaneously from pairs of ventricular fibers in an isolated, regularly beating preparation. A double-barrelled microelectrode was used to record the potentials from, and to polarize, one fiber. A single microelectrode was used to record from a distant fiber. The existence of two systems of fibers, termed P and V, was confirmed. Histological evidence for the existence of two types of fibers is also presented. Electrotonic current spread was observed within both systems, electrotonic interaction between the two systems was rare and always weak. In the case of those pairs of fibers showing electrotonic interaction, the distance for an e-fold decrease in magnitude of the electrotonic potentials was found to be from 300 to 600 µ in P fibers and from 100 to 300 µ in V fibers. However, no electrotonic interaction could be observed in the majority of V fiber pairs. Moreover, the magnitude of the electrotonic potential did not decay monotonically with distance in any one direction. It is concluded that the rabbit ventricle cannot be regarded as a single freely interconnected syncytium.     

Bacterial Flora of the Hemolymph of the Blue Crab, Callinectes sapidus: Most Probable Numbers

The hemolymph of 290 freshly collected blue crabs from Chincoteague Bay, Va., was sampled over a 15-month period from August 1968 through November 1969 and most probable numbers of bacteria were determined by tube dilution. The hemolymph of 18% of all crabs sampled was found to be sterile, with 16% sterility in summer and 23% in winter samples. Despite individual variations, male crabs as a group had a higher bacterial hemolymph burden than females, and among both sexes summer counts were higher than winter. The hemolymph of crabs with missing appendages had significantly higher counts than uninjured crabs. The annual mean hemolymph most probable numbers per ml was 2,756 for males, 1,300 for females, and 1,876 for both sexes. The higher bacterial levels found in the hemolymph of male crabs may, in part, be explained by the fact that males, which predominated in the summer samples, had a higher incidence of injury and missing appendages than did females.     

Measurement of Maximum Isometric Force Generated by Permeabilized Skeletal Muscle Fibers

Analysis of the contractile properties of chemically skinned, or permeabilized, skeletal muscle fibers offers a powerful means by which to assess muscle function at the level of the single muscle cell. Single muscle fiber studies are useful in both basic science and clinical studies. For basic studies, single muscle fiber contractility measurements allow investigation of fundamental mechanisms of force production, and analysis of muscle function in the context of genetic manipulations. Clinically, single muscle fiber studies provide useful insight into the impact of injury and disease on muscle function, and may be used to guide the understanding of muscular pathologies. In this video article we outline the steps required to prepare and isolate an individual skeletal muscle fiber segment, attach it to force-measuring apparatus, activate it to produce maximum isometric force, and estimate its cross-sectional area for the purpose of normalizing the force produced.