THE POTASSIUM EQUILIBRIUM IN MUSCLE

1. Analyses were made of the K and HCO₃ content, the irritability, and weight change of isolated frog sartorius muscles after immersion for 5 hours in Ringer''s solutions modified as to pH and potassium content. 2. At each pH a concentration of potassium in the solution was found which was in diffusion equilibrium with the potassium in the muscle. In greater concentrations potassium moved into the muscle against the concentration gradient and vice versa. 3. The greater the alkalinity of the solution the smaller the concentration of the potassium at equilibrium so that the product of the concentrations of OH and K in the solution at equilibrium tends to remain approximately constant. 4. The pH inside the muscle is approximately equal to that outside when first dissected but it tends to change during immersion so as to follow the changes in the pH of the solution. This finding is in direct conflict with the theory according to which the high potassium concentration inside should be accompanied by an equally high hydrogen ion concentration in relation to that outside. 5. The diffusion of potassium into the muscle makes its contents more alkaline but the increase in alkalinity is not always, nor usually, equivalent to the amount of potassium which has diffused and conversely, the pH inside can change in either direction according to the pH outside without there being any diffusion of potassium. Hence potassium is not the only penetrating ion. 6. The irritability of the muscles is at a maximum in concentrations of potassium which are greater than that in normal Ringer''s solution, or about 20 mg. per cent potassium. This optimum does not seem to be a function of pH and is therefore not dependent upon the direction of movement of the potassium but probably on the ratio of potassium outside to that inside. 7. Swelling of the muscles occurs in solutions which injure the muscle so as to permit both cations and anions to enter without permitting the organic protein anions to escape. Anion impermeability is necessary to prevent this same osmotic swelling under normal conditions. 8. An increase in the CO₂ tension in muscle and solution causes a greater increase in acidity in the solution than in the muscle and leads to a loss of potassium. One expects therefore a potassium shift from tissues to blood comparable to the chlorine shift from plasma to corpuscles.     

Changes in ATPase and SDH reactions of the rat extrafusal and intrafusal muscle fibres after preincubations at different pH.

The dependence of adenosine-triphosphatase (ATPase) and succinic dehydrogenase (SDH) histochemical reactions on the pH of the preincubation medium was studied in serial cross sections of 1- to 6-month-old rat extensor digitorum longus (EDL) and soleus (SOL) muscles. The use of a wide spectrum of pH values confirmed the previous results showing that: (1) according to their ATPase and SDH reactions 3 types of extrafusal muscle fibres, i.e., fast-twitch glycolytic (FG), fast-twitch oxidative-glycolytic (FOG) and slow-twitch oxidative (SO) and 3 types of intrafusal muscle fibres, i.e. typical and intermediate nuclear bag fibres and nuclear chain fibres were observed; (2) only acid preincubation (pH 4.35) is necessary to demonstrate the reversal of the ATPase reaction; while (3) alkali preincubation (pH 10.4) does not provide any new important information as compared with ATPase without preincubation. Furthermore, it was shown that: (4) fast-twitch muscle fibres exhibited high ATPase activity on preincubations at pH 4.9 to 10.4, slow-twitch fibres had very high ATPase activity on preincubation at pH 4.3 and 4.5; (5) after preincubation at pH 4.5 two types of FOG fibres were observed, differing in their ATPase activity; (6) in both muscles there were fibres with intermediate ATPase activity both after acid and/or alkali preincubations; (7) the intrafusal muscle fibres exhibited some specific characteristics when compared with extrafusal fibres. In contrast to the ATPase reactions, SDH activity was decreased equally, in both extra- and intrafusal fibres, with increasing acidity and alkality of the preincubation medium.     

Changes in ATPase and SDH reactions of the rat extrafusal and intrafusal muscle fibres after preincubations at different pH

Summary The dependence of adenosine-triphosphatase (ATPase) and succinic dehydrogenase (SDH) histochemical reactions on the pH of the preincubation medium was studied in serial cross sections of 1- to 6-month-old rat extensor digitorum longus (EDL) and soleus (SOL) muscles.The use of a wide spectrum of pH values confirmed the previous results showing that: (1) according to their ATPase and SDH reactions 3 types of extrafusal muscle fibres, i.e., fast-twitch glycolytic (FG), fast-twitch oxidative-glycolytic (FOG) and slow-twitch oxidative (SO) and 3 types of intrafusal muscle fibres, i.e. typical and intermediate nuclear bag fibres and nuclear chain fibres were observed; (2) only acid preincubation (pH 4.35) is necessary to demonstrate the reversal of the ATPase reaction; while (3) alkali preincubation (pH 10.4) does not provide any new important information as compared with ATPase without preincubation. Furthermore, it was shown that: (4) fast-twitch muscle fibres exhibited high ATPase activity on preincubations at pH 4.9 to 10.4, slow-twitch fibres had very high ATPase activity on preincubation at pH 4.3 and 4.5; (5) after preincubation at pH 4.5 two types of FOG fibres were observed, differing in their ATPase activity; (6) in both muscles there were fibres with intermediate ATPase activity both after acid and/or alkali preincubations; (7) the intrafusal muscle fibres exhibited some specific characteristics when compared with extrafusal fibres.In contrast to the ATPase reactions, SDH activity was decreased equally, in both extra- and intrafusal fibres, with increasing acidity and alkality of the preincubation medium.     

Lack of ''acid reversal'' of myofibrillar adenosine triphosphatase in masticatory muscle fibres of rhesus monkeys

Summary Myofibrillar adenosine triphosphatase (ATPase) activity was demonstrated in sections of masseter and temporalis muscles and of selected limb muscles of adult rhesus monkeys. Incubations were performed either with no pre-treatment or after prior incubation in alkaline media (pH 10.2–10.4) or acidic media (pH 3.8–4.6). Without pre-treatment, fibres having high or low ATPase activity were observed in limb and masticatory muscles. Following alkaline pre-incubation the difference between high and low ATPase of limb muscle fibres is accentuated, whereas pre-incubation in acidic media (pH 4.3) results in inhibition of high and potentiation of low ATPase activities (acid reversal). While pre-incubation of masticatory muscle sections at pH 10.2 accentuates differences in ATPase activity, pre-incubation at pH 10.4 abolishes ATPase activity. In contrast, masticatory muscle fibres showed no reversal of ATPase activity following acidic pre-incubation (pH 4.3). Pre-incubation at pH 3.8 abolished the ATPase activity of both limb and masticatory muscle fibres. The biochemical basis for the differences in ATPase histochemistry between masticatory and limb muscles is not known.     

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.     

Muscle fibre composition of the eye muscles of the carp (Cyprinus carpio L.) defined on the base of histochemical observations

A histochemical study has been carried out on the eye muscles of the carp. On the base of the ATP-ase and SDH activity and with regard to the localization and diameter of muscle fibres six types of muscle fibres situated in the defined zones can be distinguished. The type 1 and 2 fibres display a moderately high ATP-ase activity at pH 9.4 and rather low activity after alkaline and acid preincubation. Type 1 shows a high SDH activity in contrast to type 2 with a low SDH activity. The other four types of fibres have the high ATP-ase activity at pH 9.4. Type 3 contains fibres with a moderately high ATP-ase activity after alkaline preincubation with a rather low activity after acid preincubation and with a low SDH activity. The fibres of type 4 characterized by the high ATP-ase activity after alkaline and acid preincubation and by the high SDH activity. The fibres of type 5 display high ATP-ase activity after alkaline and acid preincubation and the low SDH activity. They are situated in the white and intermediate fibre zones. The fibres of type 6 are comparable to the fibres of type 5, however they differ diameter and localization, i.e. they are situated in small diameter fibre zone. Using the electron microscope four types of fibres (A, B, C, and D) are found. They vary in the localization of T system, the organization of Z-line and in M-line appearance. In the type B of muscle fibres two different localizations of T system have been discerned.     

Myosin light chain patterns of individual fast and slow-twitch fibres of rabbit muscles

Summary Single muscle fibres were isolated by microdissection from freeze-dried samples of rabbit psoas and soleus muscles. The individual fibres were typed according to qualitative histochemical reactions for succinate dehydrogenase or NADH-tetrazolium reductase and for alkaline Ca²⁺-activated myofibrillar myosin ATPase after acid or alkaline preincubation. Methods are described for electrophoretic analysis by means of polyacrylamide disc electrophoresis in the presence of SDS of total myofibrillar proteins in single fibres after pre-extraction of soluble proteins. Fast-twitch white fibres revealed a myosin light chain pattern characteristic of fast-type myosin with three light chains of apparent molecular weights of 22,300 (LC₁), 18,400 (LC₂) and 16,000 (LC₃). Fast-twitch red fibres were indistinguishable in this respect from fast-twitch white fibres and showed an identical pattern of myosin light chains. Slow-twitch fibres could be characterized by a myosin light chain pattern typical of myosin of slow-twitch muscles with peptides of the apparent molecular weights of 23,500 (LC_1Sa), 23,000 (LC_1Sb) and 18,500 (LS_2S). Slow-twitch fibres isolated from soleus as well as from psoas muscle were indistinguishable with regard to their myosin light chain patterns, thus suggesting that fibres of the same histochemical type correspond in their myosin light chain patterns irrespective of their origin from different muscles.Dedicated to the memory of Ernest Gutmann who has contributed so much to our knowledge on differentiation of muscle and who died on August 6, 1977     

Activation of rat masticatory muscle afferent fibres by acidic pH

Abstract

Previous research findings have suggested an important role for acid sensing ion channels (ASICs) in muscle pain mechanisms. This study was conducted to determine if masticatory muscle afferent fibres express ASICs, if there are sex differences in this expression, and to compare the effects of low pH and hypertonic saline on afferent fibres that innervate the masticatory muscle in vivo. Immunohistochemistry methods were applied to examine the expression of ASICs in trigeminal ganglion neurons, while in vivo electrophysiology techniques were employed to examine changes in masticatory muscle afferent fibre excitability. Both ASIC₁ and ASIC₃ were expressed by predominantly larger masticatory muscle ganglion neurons, but the frequency of ASIC₃ expression (56%) was significantly greater than ASIC₁ (35%). No sex-related differences in expression were identified. Injection of pH 5.8, but not pH 6.8, phosphate buffered saline evoked afferent discharges that were significantly greater than those evoked by pH 7.4 buffer (control). Since ASIC₃ channels are not activated until the pH is around 6, these results indicate that activation of both channels contributes to excitation of masticatory muscle afferent fibres. The results further show that many masticatory muscle afferent fibres, which respond to low pH, are low threshold mechanoreceptors. These findings may explain why injection of low pH solutions into the masticatory muscles of healthy humans is not associated with significant muscle pain.     

A histoenzymatic study of rat intrafusal muscle fibres

Summary The histochemical activities of myofibrillar adenosine triphosphatase (ATPase), succinic dehydrogenase (SDH) and alpha glycerophosphate dehydrogenase (-GPD) were studied in intrafusal muscle fibres of rat fast and slow muscles. The ATPase reaction was carried out after the three standard acid preincubations. The cold K₂-EDTA preincubated ATPase reaction product was similar to that seen following the regular or alkalipreincubated ATPase reaction, except that the intermediate bag fibres exhibited much higher activity after cold K₂-EDTA preincubation. Following either acetic acid solution or cold and room temperature K₂-EDTA-preincubation, followed by the ATPase reaction, chain fibres of the fast muscles vastus lateralis and extensor digitorum longus exhibited a very low amount of reaction product as compared with those of the slow soleus. Veronal acetate and K₂-EDTA preincubations (and equally preincubation in acetic acid solution) resulted in acid stable ATPase activity along the entire length of the typical bag fibres but only in the polar regions of the intermediate bag fibres. On the basis of differing -GPD reaction, two sub populations of nuclear chain fibres were discovered in one spindle. It is a matter of conjecture, to what extent the histochemical differences of intrafusal fibres from fast and slow muscles reflects functional distinctions in the response to stretch of muscle spindles from fast and slow muscles.     

Borate complexes of amphotericin B: Polymeric species and aggregates in aqueous solutions

Amphotericin B, a polyene macrolide antibiotic, exists in aqueous solution as a poorly soluble, high-molecular-weight aggregate. A borate complex of this polyene was prepared that has greater solubility and is less aggregated. In aqueous solution this borate complex exists as a mixture of several molecular species differing in borate content, molecular weight, and molecular conformation. The solubility varied with pH and was minimal at neutrality. Throughout the pH range it was one to two orders of magnitude higher than that of the parent compound. The molecular size distribution, as determined by differential ultrafiltration, showed a progressive increase in the weight fraction of aggregates going from acid to alkaline solutions. The sizes of aggregates ranged from under 25 to over 100 molecules. The borate content of the complexes increased with increasing pH. No borate was complexed in acid solutions. This indicated that amphotericin B and borate ions can complex to form copolymer chains of varying length in which these species alternate, since both are bifunctional. The complexation equilibrium is favored by high pH. Absorption and CD spectra indicated that the polyene molecules can stack reversibly to form dimers. Dimerization constants calculated from the spectra were highest in neutral solution and declined with increasing acidity or alkalinity. In alkaline solutions the polymer chains are long and extended, with minimal stacking. In neutral solution the chains are shorter and extensively stacked. In acid solutions no borate complexes are formed, and the polyenes are stacked to an intermediate degree. The very different effects of pH and concentration on the degree of complexation with borate and on the degree of dimerization of the polyenes shows that these equilibria are independent of each other.     

Renal response to secretin.

The effect of Jorpes secretin on the urinary volume, pH, and excretion of sodium, potassium, chloride, bicarbonate, titratable acidity, ammonia and phosphate was studied in five healthy male volunteers with and without simultaneous aspiration of duodenal fluids. A three- to fourfold increase in urinary volume and sodium excretion occurred within the first 30 min after secretin injection and this was accompanied by a significant rise in urinary pH in each instance. Urinary bicarbonate excretion increased from 55 plus or minus 13 to 395 plus or minus 33 mueq/30 min after secretin injection. Aspiration of alkaline duodenal contents was accompanied by an even greater postsecretin increase in urinary bicarbonate excretion. No significant changes in arterial pH or blood gases were detected throughout the study. These observations are compatible with a direct effect of secretin upon the renal tubular reabsorption of water, bicarbonate, and other ions, and could account for the transient alterations in urinary pH occurring in response to a meal.     

THE EFFECT OF PURE PROTEIN SOLUTIONS AND OF BLOOD SERUM ON THE DIFFUSIBILITY OF CALCIUM

1. A comparative study has been made of the diffusibility of calcium in solutions of crystalline egg albumin, serum globulin, and human blood serum. 2. In all three of these solutions, at pH 7.4, molal Ca concentrations within the membrane are greater than the calcium concentrations in the outside solutions, quite in accordance with the Donnan theory. 3. At pH 7.4, the ratio of See PDF for Structure varies directly with the protein concentration whether the solution be one of egg albumin, serum globulin, or blood serum. This is also in accordance with the Donnan theory. 4. On the acid side of the isoelectric point of the proteins, the concentration of Ca outside becomes greater than the concentration in the solution of blood serum or pure protein, as is demanded by the Donnan theory. 5. The magnitude of the Ca ratios on the alkaline and acid sides of the isoelectric points is probably the resultant of the Donnan equilibrium and the formation of complex Ca-protein ions. Northrop and Kunitz have shown the probability of the existence of such ions in the case of Zn⁺⁺, K⁺, and Li⁺, where satisfactory electrodes have been developed for E.M.F. measurements.     

THE PENETRATION OF AMMONIA INTO FROG MUSCLE

1. A study was made of the electrolyte changes which occur when frog muscles are immersed in a Ringer solution with 1/5 of the Na replaced by NH₄Cl. Analyses were made in the solution and in the muscles for K and NH₃, and the muscles were also analyzed for Cl, HCO₃, and Na. Control muscles were immersed in normal Ringer''s solution and similarly analyzed. 2. The amount of ammonia taken up was about equal to the K and Na lost. There was also a small increase in chloride content. The bicarbonate content was the same in both experimental and control muscles, indicating no change in the muscle pH due to the NH₃ which penetrated. An increased loss of K due to the penetration of NH₃ was also demonstrated by the use of radioactive K. 3. After 5 hours, the concentration of ammonia per gram of muscle is about the same as the concentration in the solution. After 4 or 5 days, the concentration in the muscle is about 1.5 times that in the solution. The inside to outside NH₃ ratio is about equal to the corresponding H ion ratio, but is much less than the K ratio. 4. The rate of penetration of the NH₃ is increased by a rise of temperature, by stirring the solution, and by decrease in the concentration of Na, K, Ca, or Mg in the solution; it is decreased by increasing the size of the muscles or by killing them with chloroform or boiling. 5. Liver, smooth muscle, skin, and kidney, in a few experiments, behaved much like muscle except that there was a formation of urea in the case of liver. 6. The injection of NH₄Cl into anesthetized cats causes an increase in the level of K in the blood plasma.     

Analysis of phosphate metabolites, the intracellular pH, and the state of adenosine triphosphate in intact muscle by phosphorus nuclear magnetic resonance.

31P nuclear magnetic resonance spectra recorded from intact muophosphate, and the sugar phosphates. Quantitation of these metabolites by 31P nuclear magnetic resonance was in good agreement with values obtained by chemical analyses. The spectra obtained from various muscles showed considerable variation in their phosphorus profile. Thus, differences could be detected between (a) normal and diseased muscle; (b) vertebrates and invertebrates; (c) different species of the same animal. The time course of change in phosphate metabolites in frog muscle showed that ATP level remains unchanged until phosphocreatine is nearly depleted. Comparative studies revealed that under anaerobic conditions the Northern frog maintains its ATP content for 7 hours, while other types of amphibian, bird, and mammalian muscles begin to show an appreciable decay in ATP after 2 hours. Several lines of evidence indicated that ATP forms a complex with magnesium in the muscle water: (a) the phosphate resonances of ATP in the muscle were shifted downfield as compared to those in the alkaline earth metal-free perchloric acid extract of the muscle; (b) the coupling constants of ATP measured in various live muscles closely corresponded to those for MgATP in a solution resembling the composition of the muscle water; (c) in the muscle the gamma-phosphate group of ATP exhibited no shift change over a period of 10 hours under conditions where resonances of other phosphate compounds could be titrated. This behavior is similar to that of MgATP in model solutions in the physiological pH range, and it is different from that of CaATP. The chemical shifts of the phosphate metabolites were determined in several relevant solutions as a function of pH. Under all conditions only inorganic orthophosphate showed an invariant titration curve. From the chemical shift of inorganic phosphate observed during aging of intact muscle the intracellular pH of frog muscle was estimated to be 7.2.     

INACTIVATION OF CRYSTALLINE TRYPSIN

1. The rate of inactivation of crystalline trypsin solutions and the nature of the products formed during the inactivation at various pH at temperatures below 37°C. have been studied. 2. The inactivation may be reversible or irreversible. Reversible inactivation is accompanied by the formation of reversibly denatured protein. This denatured protein exists in equilibrium with the native active protein and the equilibrium is shifted towards the denatured form by raising the temperature or by increasing the alkalinity. The decrease in the fraction of active enzyme present (due to the formation of this reversibly denatured protein) as the pH is increased from 8.0 to 12.0 accounts for the decrease in the rate of digestion of proteins by trypsin in this range of pH. 3. The loss of activity at high temperatures or in alkaline solutions, just described, is very rapid and is completely reversible for a short time only. If the solutions are allowed to stand the loss in activity becomes gradually irreversible and is accompanied by the appearance of various reaction products the nature of which depends upon the temperature and pH of the solution. 4. On the acid side of pH 2.0 the trypsin protein is changed to an inactive form which is irreversibly denatured by heat. The course of the reaction in this range is monomolecular and its velocity increases as the acidity increases. 5. From pH 2.0 to 9.0 trypsin protein is slowly hydrolyzed. The course of the inactivation in this range of pH is bimolecular and its velocity increases as the alkalinity increases to pH 10.0 and then decreases. As a result of these two reactions there is a point of maximum stability at about pH 2.3. 6. On the alkaline side of pH 13.0 the reaction is similar to that in strong acid solution and consists in the formation of inactive protein. The course of the reaction is monomolecular and the velocity increases with increasing alkalinity. From pH 9.0 to 12.0 some hydrolysis takes place and some inactive protein is formed and the course of the reaction is represented by the sum of a bi- and monomolecular reaction. The rate of hydrolysis decreases as the solution becomes more alkaline than pH 10.0 while the rate of formation of inactive protein increases so that there is a second point at about pH 13.0 at which the rate of inactivation is a minimum. In general the decrease in activity under all these conditions is proportional to the decrease in the concentration of the trypsin protein. Equations have been derived which agree quantitatively with the various inactivation experiments.     

A histoenzymatic study of rat intrafusal muscle fibres.

The histochemical activities of myofibrillar adenosine triphosphatase (ATPase), succinic dehydrogenase (SDH) and alpha glycerophosphate dehydrogenase (alpha-GPD) were studied in intrafusal muscle fibres of rat fast and slow muscles. The ATPase reaction was carried out after the three standard acid preincubations. The cold K2-EDTA preincubated ATPase reaction product was similar to that seen following the regular or alkali-preincubated ATPase reaction, except that the intermediate bag fibres exhibited much higher activity after cold K2-EDTA preincubation. Following either acetic acid solution or cold and room temperature K2-EDTA-preincubation, followed by the ATPase reaction, chain fibres of the fast muscles vastus lateralis and extensor digitorum longus exhibited a very low amount of reaction product as compared with those of the slow soleus. Veronal acetate and K2-EDTA preincubations (and equally preincubation in acetic acid solution) resulted in acid stable ATPase activity along the entire length of the typical bag fibres but only in the polar regions of the intermediate bag fibres. On the basis of differing alpha-GPD reaction, two sub populations of nuclear chain fibres were discovered in one spindle. It is a matter of conjecture, to what extent the histochemical differences of intrafusal fibres from fast and slow muscles reflects functional distinctions in the response to stretch of muscle spindles from fast and slow muscles.     

Proton fluxes associated with erythrocyte membrane anion exchange

Summary Transient extracellular pH changes accompany the exchange of chloride for sulfate across the erythrocyte membrane. The direction of the extracellular pH change during chloride efflux and sulfate influx depends on experimental conditions. When bicarbonate is present, the extracellular pH drops sharply at the outset of the anion exchange and tends to follow the partial ionic equilibrium described by Wilbrandt (W. Wilbrandt, 1942.Pfluegers Arch. 246:291). When bicarbonate is absent, however, the anion exchange causes the pH to rise, indicating that protons are cotransported with sulfate during chloridesulfate exchange. The pH rise can be reversed by the addition of HCO ₃ ^– (4 m) or 2,4-dinitrophenol (90 m). This demonstrates that the proton-sulfate cotransport can drive proton transport uphill. The stoichiometry of the transport is that one chloríde exchanges for one sulfate plus one proton. These results support the titratable carrier model proposed by Gunn (Gunn, R.B. 1972.In: Oxygen Affinity of Hemoglobin and Red Cell Acid-Base Status. M. Roth and P. Astrup, editors. p. 823. Munksgaard, Copenhagen) for erythrocyte membrane anion exchange.     

On the heterogeneity of capillaries of pigeon pectoralis muscle: a histoenzymatic and ultrastructural study

Synopsis Earlier studies had failed to show the presence of capillaries between the white fibres of pigeon pectoralis muscle. In this paper, data are reported for the first time documenting that these capillaries occur in both intra- and inter-fasicular areas of the muscle. Fresh frozen sections of pigeon pectoralis major muscle were incubated for alkaline ATPase reaction following pretreatment with different EDTA solutions (4.3 mM, pH 4.3). The results showed the existence of an inherent heterogeneity of capillaries. The capillaries of white fibres stained intensely for K^–/Mg^2–-EDTA or Mg²⁺-EDTA pre-incubated ATPase; the capillaries of red fibres stained poorly. Both white fibre and red fibre capillaries were examined ultrastructurally in the non-perfused pigeon pectoralis muscle. It is suggested that a possible correlation exists between the distinctive metabolic and mechanical characteristics of the Type II white, glycolytic, fast-twitch fast-fatigue muscle fibres and the high ATPase activity of their capillaries.     

The claw closer muscle of two estuarine crab species,Cyrtograpsus angulatus and Neohelice granulata (Grapsoidea,Varunidae): histochemical fibre type composition

Longo, M.V. and Díaz, A.O. (2011). The claw closer muscle of two estuarine crab species, Cyrtograpsus angulatus and Neohelice granulata (Grapsoidea, Varunidae): histochemical fibre type composition. —Acta Zoologica (Stockholm) 00 : 1–7. This study permitted the characterization of four types of muscle fibres in the claw closer muscles of Cyrtograpsus angulatus and Neohelice granulata. Succinic dehydrogenase (SDH) for mitochondria, periodic acid Schiff (PAS) for glycogen, Sudan Black B for lipids and myosin‐adenosine triphosphatase (m‐ATPase) preincubated at alkaline and acid pHs were used for that purpose. The mean fibre diameters, the relative areas and frequencies of each muscle fibre type were calculated. Types I and IV would be considered ‘extreme’ groups with type I fibres large, weak and acid/alkaline‐labile m‐ATPase, weak SDH, PAS and Sudan, and type IV fibres small, very strong and acid/alkaline‐resistant m‐ATPase, strong SDH and PAS, and moderate Sudan. Types II and III would belong to a predominant ‘intermediate’ group. Type IV fibres were scarce in C. angulatus but represented 25% of the total fibre population in N. granulata. In C. angulatus, the relative area occupied by type I fibres was bigger than its relative proportion, whereas in N. granulata, types I and II had similar patterns. Concluding, variations in fibre type composition in the claw closer muscles of C. angulatus and N. granulata would be linked to different habitats and feeding behaviours.     

THE COLLOIDAL BEHAVIOR OF PROTEINS

1. It is well known that neutral salts depress the osmotic pressure, swelling, and viscosity of protein-acid salts. Measurements of the P.D. between gelatin chloride solutions contained in a collodion bag and an outside aqueous solution show that the salt depresses the P.D. in the same proportion as it depresses the osmotic pressure of the gelatin chloride solution. 2. Measurements of the hydrogen ion concentration inside the gelatin chloride solution and in the outside aqueous solution show that the difference in pH of the two solutions allows us to calculate the P.D. quantitatively on the basis of the Nernst formula See PDF for Equation if we assume that the P.D. is due to a difference in the hydrogen ion concentration on the two sides of the membrane. 3. This difference in pH inside minus pH outside solution seems to be the consequence of the Donnan membrane equilibrium, which only supposes that one of the ions in solution cannot diffuse through the membrane. It is immaterial for this equilibrium whether the non-diffusible ion is a crystalloid or a colloid. 4. When acid is added to isoelectric gelatin the osmotic pressure rises at first with increasing hydrogen ion concentration, reaches a maximum at pH 3.5, and then falls again with further fall of the pH. It is shown that the P.D. of the gelatin chloride solution shows the same variation with the pH (except that it reaches its maximum at pH of about 3.9) and that the P.D. can be calculated from the difference of pH inside minus pH outside on the basis of Nernst''s formula. 5. It was found in preceding papers that the osmotic pressure of gelatin sulfate solutions is only about one-half of that of gelatin chloride or gelatin phosphate solutions of the same pH and the same concentration of originally isoelectric gelatin; and that the osmotic pressure of gelatin oxalate solutions is almost but not quite the same as that of the gelatin chloride solutions of the same pH and concentration of originally isoelectric gelatin. It was found that the curves for the values for P.D. of these four gelatin salts are parallel to the curves of their osmotic pressure and that the values for pH inside minus pH outside multiplied by 58 give approximately the millivolts of these P.D. In this preliminary note only the influence of the concentration of the hydrogen ions on the P.D. has been taken into consideration. In the fuller paper, which is to follow, the possible influence of the concentration of the anions on this quantity will have to be discussed.