Electron transfer catalyzed by manganese tetratolyl-prophyrinate across poly(γ-methyl L-glutamate) membrane

A poly(γ-methyl L -glutamate) (PMLG) membrane containing manganese tetratolylporphyrinate (MnTTP) was prepared in order to examine the transmembrane electron transfer in a redox system constructed as S₂O₄^2?/membrane/Fe(CN)₆^3?. Electron transfer was observed in 0,1 M pH 7,0 imidazole (Im) buffer but not in 0,1 M pH 7,0 phosphate buffer. The apparent transfer rate increased with MnTTP content and also with the Im concentration in the buffer, indicating that electron is transferred by MnTTP, which is coupled with proton transport by Im distributed in the membrane. The transfer catalyzed by MnTTP was more effectively accelerated with Im than with 2-methylimidazole (2-Melm) but not at all with 1-methylimidazole (1-Melm). This implies that the 1-N site on the imidazoles as the axial ligand of MnTTP is a crucial position for the mediation of electron transfer between MnTTP's. In the pH range 6,0–8,5 of Im buffer, the electron transfer rate showed a maximum at pH 7,0. This pH dependence is discussed in terms of the concentration and mobility of proton in the membrane.     

Proton secretion in the upper part of the descending limb of long-looped nephron from hamsters

 The proton transport processes in the upper part of the descending limb of the long-looped nephron (LDLu) from hamsters were studied using a fluorescent dye, 2′,7′-bis(carboxyethyl)carboxyfluorescein (BCECF) in microperfused single nephron preparations. Intracellular pH (pH_i), as assessed by the measurement of the fluorescence of BCECF trapped in the cytoplasm, was 7.23 ± 0.05 (n = 18) under nominally HCO₃ ^–-free conditions. Ouabain, when added to the bath, decreased pH_i by 0.22 units. After an NH₄Cl prepulse, the initial proton extrusion rate was 1.23 ± 0.26 (n = 9) pH units/min, and was retarded in the presence of 1 mM amiloride either in the bath or in the lumen. pH_i failed to recover when Na⁺ was eliminated from ambient solutions. These observations suggest that Na⁺/H⁺ antiporters exist both in the apical and basolateral cell membranes. By measuring tubular fluid pH (pH_t) under stopped flow conditions, we examined whether the hamster LDLu has the capacity to generate and maintain a transmural H⁺ gradient. After the tubular outflow was obstructed, the luminal fluid was rapidly acidified, reaching a steady-state pH of 6.84 ± 0.09 (n = 7). The steady-state pH was influenced by bath pH. Tubular fluid acidification was not observed in the absence of Na⁺ and was prevented by ouabain. We conclude that the hamster LDLu has the capability to generate and maintain a transmural proton gradient by proton secretion via a luminal Na⁺/H⁺ antiporter which is secondarily driven by the Na⁺-K⁺ ATPase in the basolateral membrane. Received: 18 February 1997 / Received after revision: 23 June 1997 / Accepted: 14 July 1997     

Confocal imaging of calcium release events in single smooth muscle cells

Localized [Ca²⁺]_i transients (‘sparks’) first directly detected in cardiac myocytes were considered to represent ‘elementary’ Ca²⁺-release events playing a key role during excitation–contraction coupling ( Cheng et al. 1993 ). In this study we employed confocal [Ca²⁺]_i imaging to characterize subcellular calcium signalling in fluo-3 loaded visceral and vascular smooth muscle cells. In some experiments membrane potential of the myocyte was controlled using whole-cell patch clamp technique and changes in membrane current were recorded simultaneously with [Ca²⁺]_i imaging. Some local [Ca²⁺]_i transients were very similar to ‘Ca²⁺ sparks’ observed in heart, i.e. lasting ≈200 ms with a peak fluorescence ratio of 1.75 ± 0.23 (mean ± SD, n = 33). Ca²⁺ sparks were found to occur in certain preferred locations in the cell, termed frequent discharge sites. Other events were faster and smaller, lasting only ≈40 ms with a peak normalized fluorescence of 1.36 ± 0.09 (mean ± SD, n = 28). A high correlation between spontaneous transient outward currents and spark occurrence was observed. Proliferating waves of elevated [Ca²⁺]_i initiated during membrane depolarization seem to arise from spatio-temporal recruitment of local Ca²⁺-release events. The spatial non-uniformity of sarcoplasmic reticulum and ryanodine receptor distribution within the cell may account for the existence of ‘frequent discharge sites’ and the wide variation in the Ca²⁺ wave propagation velocities observed.     

Thermoresponsive Properties of Sugar Sensitive Copolymer of N‐Isopropylacrylamide and 3‐(Acrylamido)phenylboronic Acid

Summary: The copolymer of N‐isopropylacrylamide and 3‐(acrylamido)phenylboronic acid (82:18, = 47 000 g · mol^?1) was prepared by free radical polymerization. The copolymer showed typical thermal precipitation behavior in aqueous solutions, its precipitation temperature (T_P) being increased from 23 to 32 °C by increasing the pH from 6.5 to 9.7, because of ionization of the phenylboronate units. The pK_a was evaluated as 8.9 ± 0.1 from the effect of pH on T_P. At pH > 9, i.e., in the anionic form of the copolymer, T_P was affected by a very low concentration of glucose (5.6 μM , ΔT_P = 1–1.5 °C), because of complex formation with a high binding constant. At a higher concentration of polyols (560 μM , pH > 8) the increase of T_P was maximal for the copolymer complexes with fructose (7–10 °C) and decreased in the order: fructose > glucose ≈ mannitol > pentaerythritol > galactose > Tris >glycerol. Di‐ and oligosaccharides (lactose, sucrose, and dextran) caused a slight increase of T_P at pH 7.5–8.7 while no effect was observed at pH > 9. Isothermal dissolution of the copolymer suspension in water (27 °C, pH 8.5) was possible in the presence of fructose or mannitol but required higher concentrations (1.4–3.6 × 10³ μM ) as compared to those which enabled the shift of T_P in the soluble copolymer. The dissolution rate increased with fructose concentrations.

Effect of pH on T_P of poly(NIPAAM‐co‐AAPBA) in the presence of various monosaccharides.     

Polymers containing enzymatically degradable bonds, 7. Design of oligopeptide side-chains in poly[N-(2-hydroxypropyl)methacrylamide] copolymers to promote efficient degradation by lysosomal enzymes

N-(2-Hydroxypropyl)methacrylamide copolymers are considered to be a potential drug delivery system. To fulfil this role the drug-polymer linkage must be susceptible to intralysosomal hydrolysis. Taking p-nitroanilide as a drug analogue, copolymers were synthesized bearing oligopeptidyl-p-nitroanilide side-chains designed to match known specificities of the lysosomal enzymes cathepsin L or cathepsin D. Degradation of side-chains by rat liver lysosomal enzymes (measured by monitoring terminal p-nitroaniline release) occurred only in the presence of reduced glutathione (5 mmol/l) and was effectively inhibited by leupeptin, indicating the involvement of thiol-proteinases in every case. Depending on side-chain composition, between 20 and more than 50% of the terminal p-nitroaniline residues were liberated during a 5 h incubation. It has also been shown that 1) a polymer molecule may contain side-chains of a single type that are nevertheless differentially susceptible to lysosomal hydrolysis; 2) two of the side-chains studied liberate only a p-nitroaniline residue, whereas the others also release amino-acyl-p-nitroanilides; 3) the cleavage of all side-chains displays a broad pH optimum pH 5 to pH 7; 4) the Michaelis-Menten constant K_m for side-chain cleavage varied between 26,1 and 143,2 mg/ml, depending on the amino acid sequence of the side-chain.     

Poly(propylene sulfoxide) — a first approach to a dipolar aprotic,water-soluble and reactive polymer

The oxidation of atactic poly(2-methylthiirane) (PPS, M?_w ≈ 1 – 2 · 10⁵) to its corresponding sulfoxide (PPSO) is studied under a variety of experimental conditions: m-chloroperbenzoic acid in homogeneous chloroform solution ( ? 7°C) and hydrogen peroxide or bromine in an interfacial chloroform-water system (20°C) lead to selective and quantitative oxidation under stoichiometric conditions with simultaneous chain degradation (M?_w (PPSO) ≈ 0,5 – 3 · 10⁴). The high density of sulfoxide functions affords to the PPSO chain a number of specific properties such as: (a) solubility in dipolar protic (CH₃OH, CHCHl₃ …) and aprotic (DMF, DMSO) solvents, the polymer coils being, however, strongly associated in aqueous solution, (b) strong polarity of the bulk polymer, as shown by an “apparent local dipole moment” of about 4,1 D, (c) poor thermal stability, degradation starting at about 130°C under nitrogen, with a weight loss of 50% at 160°C (apparent activation energy E_a = 100 kJ · mol^?1).     

3D Hollow Microspheres Assembled from 1D Polyaniline Nanowires through a Cooperation Reaction

Novel 3D hollow spheres (diameter ≈525 nm, thickness ≈70 nm) self‐assembled from 1D PANI nanofibers (diameter ≈17 nm) with conductivity of 1.11 × 10⁻¹ S · cm⁻¹ are synthesized template‐free by using FeCl₃ and salicylic acid as the oxidant and dopant, respectively. In this method, the reaction of aniline with FeCl₃ and SA to form conductive PANI and the reaction of SA with FeCl₃ to produce a color complex, assigned as Fe(OR)²⁺, wherein OR represents the ionized phenol, coexist. The coexistence of two reactions results in a cooperative effect of the micelle, where aniline/SA acts as as a soft template of the nanofibers and the color complex as a soft‐template of the spheres, to allow the self‐assembly of complex micro/nanostructures via hydrogen bonding as the driving force.

     

Micellar Behavior of Sugar‐Carrying Polystyrene in Aqueous Solution

The micellar behavior of poly [N‐p‐vinylbenzyl‐O‐β‐D ‐galactopyranosyl‐(1→4)‐D ‐gluconamide] (PVLA) were studied by fluorescent spectroscopy, dynamic light scattering (DLS), and fluorescence energy transfer experiments using fluorescent probes such as pyrene, carbazole, and anthracene. It was found that the amphiphilic PVLA formed polymer micelles in water due to the presence of the hydrophobic polystyrene backbone and hydrophilic sugar moieties. The particle size of PVLA micelles in aqueous solution were about 8.3 nm in number average. The critical micelle concentration (CMC) of PVLA was found to be about 1×10^–4 M when pyrene was used as a probe. The same results were observed from the fluorescence energy transfer experiments using carbazole and anthracene.     

Bisphosphonic Acid‐Functionalized Water‐Soluble Photoinitiators

The first bisphosphonic acid‐functionalized benzophenone (BP) and thioxanthone (TX) photoinitiators (PIs), BPBP and TXBP, are synthesized as a new class of water‐soluble PIs for free radical polymerization. BPBP shows excellent solubility (28 g L^?1) in water at ambient temperature, compared to TXBP (0.05 g L^?1) and also the commercial PI Irgacure 2959 (5 g L^?1). BPBP and TXBP show UV–vis absorption at ≈260 (ε = 12912) and 405 (ε = 3314) nm in water. Photopolymerization results demonstrate that they can successfully initiate the photopolymerization of poly(ethylene glycol) diacrylate (M_n = 250 D) in the presence of bis‐(4‐tert‐butylphenyl)‐iodonium hexafluorophosphate (Iod). The photochemical mechanisms are investigated by electron‐spin resonance‐spin trapping, fluorescence, and steady‐state photolysis techniques.     

High temperature behavior of poly[bis(2,2,2-trifluoroethoxy)phosphazene]

Mesomorphic features of poly[bis(2,2,2-trifluoroethoxy)phosphazene] (PBFP) with high (≈10⁷) and low (≈10⁴) molecular weights have been investigated by X-ray diffraction techniques, differential scanning calorimetry optical and electron microscopy, and small-angle X-ray scattering. Characterization measurements were made from room temperature to ≈300°C, which is well above T_m, the designated melting temperature of PBFP. The wide angle X-ray scattering (WAXS) may be interpreted in support of some kind of “nano-scale order” persisting above the isotropization temperature, T_m, of this polymer. There is other evidence to the contrary, namely the optical isotropicity between crossed-polars (depicts melting) and the absence of discrete small angle X-ray scattering (SAXS) under these same conditions. An attempt is made here to establish if these features above T_m are related to molecular weight.     

Monte Carlo simulation of tetrahedral chains, 4. Size and shape of linear and star-branched polymers

Linear and star-branched chains with F = 4 ? 12 arms and N = 125 ? 7685 segments covering points of a tetrahedral lattice were generated by use of a pivot algorithm. For large N, the acceptance fractions f? of attempted moves may be described by a power law f? = A · (N ? 1)^?α. Clearly, the factor A decreases with increasing functionality F, but the exponent α is independent of the number of arms and equal to the value obtained for linear chains, α ≈ 0,1. Due to the influence of the hard-core (centre) of the star, the acceptance fraction f? for small N is lower than predicted by the scaling law, yielding a stronger dependence on F than for large chains. Meansquare dimensions, i. e. mean-square radius of gyration, mean-square end-to-end distance and mean-square centre-to-end distance obey a power law dependence on chain-length (N ? 1), the exponent being ≈ 1,184 for 245 ≤ N ≤ 7685 in all cases; alternatively, the (quadratic) dimensions may be described by a corrected scaling law (N ? 1)^2v · (C₀ + C₁ · (N ? 1)^?Δ) with v = 0,588 and Δ ≈ 0,5 as proposed by renormalization group theory for linear chains. The shape asymmetry of star-branched polymers (with the same total number of segments each) decreases with increasing number of arms, but is still appreciable for F = 12, the highest number of arms examined.     

Water and electrolyte shifts with partial fluid replacement during exercise

In this study, we examined whether athletes, who typically replace only ≈50% of their fluid losses during moderate-duration endurance exercise, should attempt to replace their Na⁺ losses to maintain extracellular fluid volume. Six male cyclists performed three 90-min rides at 65% of peak O₂ uptake in a 32°C environment and ingested either no fluid (NF), 1.2?l of water (W), or saline (S) containing 100?mmol of NaCl?·?l^?1 to replace their electrolyte losses. Both W and S conditions decreased final heart rates by ≈10 betas?·?min^?1 (P?P?+ [Na⁺], Cl^? and protein but in the S and NF trials, plasma [Na⁺] continued to increase by ≈4?mEq?·?l^?1. Differences in plasma [Na⁺] had little effect on the ≈2.4?l fluid, ≈120?mEq Na⁺ and ≈50?mEq K⁺ losses in sweat and urine in the three trials. The main effects of W and S were on body fluid shifts. During the NF trial, PV and interstitial fluid (ISF) and intracellular fluid (ICF) volumes decreased by ≈0.1, 1.2 and 1.0?l, respectively. In the W trial, the ≈1.2?l fluid and ≈120?mEq Na⁺ losses contracted the ISF volume, and in the S trial, ISF volume was maintained by the movement of water from the ICF. Since the W and S trials were equally effective in maintaining PV, Na⁺ ingestion may not be of much advantage to athletes who typically replace only ≈50% of their fluid losses during competitive endurance exercise.     

Viscosity of aqueous and alkaline solutions of poly(ethylene oxide)

Viscosity measurements over a wide range of temperature were made on aqueous solutions of poly(ethylene oxide) samples of different molar mass and of low polydispersity. Above ca. 308 K the Mark-Houwink exponent decreases and tends to a value of 0,50 at a lower critical solution temperature of 376 ± 2 K. The same value for this θ-temperature is derived also as that at which the slope of Stockmayer-Fixman plots tends to zero. At 298 K the unperturbed dimensions [〈r²〉₀/M]^1/2 = 0,089 nm · g^?1/2 · mol^1/2 and their temperature coefficient d ln 〈r²〉₀/dT ≈ ? 1,5 (±0,5) · 10^?3 K^?1. In aq. KOH the intrinsic viscosity [η] is virtually uninfluenced by pH at low-medium pH, but at high pH, [η] falls sharply. Viscosity and phase separation measurements yield θ-conditions in 1,24 M aq. KOH at 298 K. The derived polymer-water interaction parameters χ increase from 0,449 at 276 K to 0,493 at 358 K, but the enthaplic component χ_H is incapable of yielding a meaningful value for the solubility parameter δ₂ of the polymer in such a hydrogen-bonding system. The calculated value of χ₂ was 18,9 (kJ · dm^?3)^1/2.     

Diphenylphosphoryl‐Triazole‐Tethered,AIEE‐Type Conjugated Polymer as Optical Probe for Silver Ion in Relatively High‐Water‐Fraction Medium

A type of conjugated polymer ( P3 ) with the feature of aggregation‐induced emission enhancement, and with diphenylphosphoryl‐triazole (DPPT) attachment, was successfully synthesized by Cu⁺‐catalyzed click postpolymerization. P3 displayed specific optical response toward Ag⁺ in organic/aqueous mixtures with relatively high‐water‐fraction ratio (V_THF/V_water = 2:3). With the addition of Ag⁺, absorption profile of P3 exhibited obvious redshift (≈ 30 nm), accompanied by the decrease of absorbance and fluorescence (at ≈ 500 nm). As evaluated from the detailed fluorescence alteration of P3 against incremental Ag⁺, the detection limit of Ag⁺ reached ≈ 11 × 10^?9m (3σ, S/N = 3). The presence of other common background metal ions brought insignificant interference for the Ag⁺ probing by P3 . Further investigation revealed that the presence of DPPT segment played a key role for the detection of Ag⁺ by P3 .

     

Non-covalent association of heavy and light chains of human immunoglobulin G: Studies using light chain labelled with a fluorescent probe

The fluorescent probe, 5-iodoacetamidofluorescein (5-IAF), was specifically attached to the COOH-terminal cysteine residue of the L chains of two monoclonal human IgKκ proteins. The induced circular dichroism and fluorescence properties of the bound 5-IAF probe were used to study changes in its microenvironment upon reassociation of autologous or heterologous L chains and their domains with Fd' fragments. Recombination of 5-IAF-L with Fd' at pH 5.4 was accompanied by a red-shifted visible difference spectrum, an increase in the magnitude of the induced optical activity and an enhancement of fluorescence. These results were compatible with the transfer of the 5-IAF moeity to a less polar and more asymmetric environment. Equilibrium and kinetic data obtained from difference spectroscopy and fluorescence studies indicated that 5-IAF-L bound with high affinity to Fd' in a 1:1 ratio with a second-order rate constant of 1618 M^?1 sec^?1 at 25°C. Using the same approach, it was shown that the labelled constant region fragment (5-IAF-C_κ) bound to Fd' with an association constant of 5 × 10⁶ M^?1 and a forward rate constant of 30 M^?1 sec^?1. When 5-IAF-C_κ was recombined with a preformed Fd'V_κ complex, however, the intensity of the visible difference spectrum, the fluorescence emission, the binding affinity and the forward rate constant of the reaction, were significantly increased. In contrast, no spectroscopic changes were observed when V_κ was recombined with a preformed Fd'-5-IAF-C_κ complex. These data suggest that: (1) the high affinity interaction between Fd' and L results from the summation of relatively weak interactions between paired domains; (2) the binding of Vκ to Fd' modulates the reactivity of Cγl toward Cκ, probably through conformation changes transmitted via V_H-Cγl contacts; and (3) conversely, once 5-IAF-Cκ is bound to Fd', the addition of the complementary Vκ domains does not induce any detectable change in the vicinity of the fluorescent probe.     

New super-hairy semi-rigid polymers

Living monofunctional poly(tetramethylene oxyde) (PTMO) (THF bulk polymerization initiated at 20°C by methyl triflate) was end capped by reaction with 3-(dimethylamino)propyl isocyanide. Selective and quantitative quaternization of the tertiary amine function results in the straightforward synthesis of PTMO macromonomers of the isocyanide type with a fairly good control of molecular weight and polydispersity (M̄_n ≈ 1800–4400, M̄_w/M̄_n ≈ 1.2). Their homopolymerization at 40°C in highly concentrated methanol solution (macromonomer weight fraction ≈0.80) initiated by NiCl₂ quantitatively yields the corresponding poly(macromonomers) of high degrees of polymerization (DP_w > 10³) and of very unusual and maximum branching density: one graft chain per every backbone carbon atom. According to a semi-quantitative analysis of their radius of gyration, as derived from light scattering measurements (EtOAc-iPrOH 9 : 1 by vol., Et₄N⁺CF₃SO₃⁻0.05 M), an increase of the intrinsic rigidity (persistence length) of the worm-like poly-(isonitrile) backbone induced by the PTMO branches cannot be ruled out. These super-hairy polymers may be considered as exotic comb-shaped cationic poly(amphiphiles) of potential interest as new lyotropic and thermotropic materials.     

Poly(ether urethane)s incorporating long alkyl side-chains with terminal carboxyl groups as fatty acid mimics: synthesis,structural characterization and protein adsorption

The object of this work was to produce polyurethanes with greater affinity for albumin (Alb) and improved hemocompatibility by introduction of carboxyl-terminated alkyl side-chains that better mimic fatty acids, in contrast to methyl terminated alkyl side-chains used previously. Synthesis of poly(ether urethane)s (PEUs) with long alkyl side-chains via a multi-step solution addition polymerization is described. The synthesis is based upon the polymerization of a diisocyanate pre-polymer with various chain extenders and reaction with Br-terminated compound in the final stage. The side-chains had terminal methyl or carboxylic groups, and were attached either directly to the polymer backbone or to an oligo(ethylene glycol) spacer. The bulk structure of the PEUs was confirmed by ¹H-NMR and the surface polymer structure was characterized by ToF-SIMS. The influence of the incorporated C₁₆-alkyl, C₁₆-carboxyalkyl and oxyethylene-C₁₆-carboxyalkyl side-chains attached to the polymer backbone on fibrinogen (Fg) and Alb adsorption from blood plasma, and Fg adsorption from buffer solutions and binary mixtures with Alb was measured. Incorporation of C₁₆-alkyl or C₁₆-carboxyalkyl side-chains into PEUs caused relatively small changes in Fg and Alb adsorption. PEUs with oxyethylene-C₁₆-carboxyalkyl side-chains exhibited the lowest Fg adsorption and the highest Alb adsorption among all the tested polymers.     

Multinuclear NMR investigation of methylaluminoxane

By means of ²⁷Al, ¹H, ¹⁷O and ¹³C NMR spectroscopy the structure of the methylaluminoxane (MAO) cocatalyst of Kaminsky-Sinn catalysts was investigated. We have found that the ²⁷Al NMR resonance line of MAO is extremely broad at room temperature (δ ≈ 60, Δω_1/2 50 ± 10 kHz). At elevated temperatures (40–120°C) MAO exhibits an ²⁷Al resonance at δ 110 ± 10, Δω_1/2 15–10 kHz, that is, within the range reported for the aluminoxane clusters [(t-Bu)Al(μ₃-O)]₆ and [(t-Bu)Al(μ₃-O)]₉ with cage structures. The ²⁷Al resonance at δ 149–153, usually attributed to MAO, belongs to AlMe₃ present in MAO samples. The ¹⁷O NMR resonance of MAO at 50°C (δ 67, Δω_1/2 1.7 kHz) is within the range typical for three-coordinate oxo ligands, but it can be attributed only to a minor part of MAO oligomers. It was shown that the intensity of ²⁷Al and ¹⁷O NMR resonances of MAO increases with increasing temperature, whereas the width of both resonances is almost constant. The results obtained lead to the conclusion that at ambient conditions MAO forms oligomers (MeAlO)_n with cage structure and MeAlO₃ environment. Upon increasing the temperature these oligomers reversibly break into smaller MAO units. Based on the ²⁷Al NMR data the average radius (R) of MAO oligomers is approximately 5.1 ± 0.3 Å at 120°C. This radius corresponds to (MeAlO)_n species with 9 < n < 14. At ambient conditions the predominant part of MAO forms oligomers with R = 7 ± 0.5 Å and 20 < n < 30.     

Phenyl-2,4,6-trimethylbenzoylphosphinates as water-soluble photoinitiators. Generation and reactivity of OṖ(C6H5)(O−) radical anions

Lithium- and magnesium phenyl-2,4,6-trimethylbenzoylphosphinates (TMPPL and TMPPM) are effective water-soluble photoinitiators for the free-radical polymerization of appropriate monomers such as acrylamide (AA) and methacrylamide (MAA) in aqueous solution. They are also capable of initiating the polymerization of other olefinic compounds such as styrene (St), methyl methacrylate (MMA) or acrylonitrile (AN) in water-containing solvent mixtures such as 1:1 water-acetonitrile mixtures. This is due to the fact that TMPPL and TMPPM undergo α-scission with a rather high quantum yield (?(α) ≈ 0,35) resulting in the formation of 2,4,6-trimethylbenzoyl radicals and O?? (C₆H₅)(O^?) radical anions. The latter are very reactive toward olefinic monomers. Bimolecular rate constants k_R+M/(L/(mol · s)) were determined by flash photolysis at room temperature, e. g. in neat water: 3,8 · 10⁸ (MAA), 2,2 · 10⁸ (AA), and in H₂O/CH₃CN (1:1, v/v): 1,8 · 10⁷ (St), 1,2 · 10⁸ (MMA), 8,4 · 10⁷ (AN).     

Skeletal muscle buffering capacity is higher in the superficial vastus than in the soleus of spontaneously running rats

Skeletal muscle buffering capacity (βm_titr) was determined in soleus (type I) and superficial vastus (type II) muscles of 16 Long–Evans rats with differing levels of spontaneous activity and in 11 sedentary control rats. βm_titr was 24% higher (P<0.001) in superficial vastus muscle than in soleus muscle (268±50 vs. 216±30 μmol H⁺ g muscle dry wt^-1 pH unit^-1) (mean±SD). There was no relationship between βm_titr and mean weekly running distance amongst spontaneously running rats, nor was βm_titr any greater in these rats than in a group of sedentary control rats. Protein to wet wt ratio was 31% higher (P<0.0001) in the superficial vastus muscle when compared with soleus muscle (22.04±3.74 vs. 16.77±3.00 mg protein, 100 mg wet wt muscle^-1), but there was no relationship between protein to wet wt ratio and running distance. Initial muscle homogenate pH (pH_i) was lower in superficial vastus muscle compared with soleus muscle (6.36±0.25 vs. 6.63±0.16). Running rats had a significantly lower pH_i in both soleus and superficial vastus than sedentary controls. There was an exponential relationship between weekly running distance and pH_i in both the superficial vastus muscle (r=-0.86, P<0.001) and the soleus muscle (r=-0.73, P<0.01). Citrate synthase activity correlated with weekly running distance in superficial vastus muscle (r=0.66, P<0.01) but not in soleus muscle. The results confirm a higher βm_titr in the type II superficial vastus muscle when compared with the predominantly type I soleus muscle. We suggest that this may be partly the result of a higher protein concentration in type II muscle. Future studies measuring βm_titr in mixed muscle (e.g. human vastus lateralis) should report fibre type composition.