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At least 19 recordsLinked to original sources

PubMed1979

The change in the load-sustaining ability and in the series elasticity in Mytilus smooth muscle during isotonic shortening.

1. The change in the ability to sustain a load and the change in the series elasticity in the anterior byssal retractor muscle (a.b.r.m.) of Mytilus edulis during isotonic shortening was studied by recording the length changes following step changes in load. 2. When a load of 0.7--0.9 P0 WAs applied after a period of isotonic shortening under a small load (0.05--0.1 P0), the muscle fibres showed continuous isotonic lengthening, indicating a reduction in the ability to sustain a load during isotonic shortening. 3. Following the application of a load of 0.3--0.6 P0 during isotonic shortening under a small load, the fibres exhibited a transient isotonic lengthening before starting to shorten isotonically, indicating some degree of restoration in the load-sustaining ability after the step increase in load. 4. No appreciable reduction in the load-sustaining ability was observed during isotonic shortening under a large load (more than 0.7 P0). 5. The load--extension curves of the series elasticity determined during isotonic shortening were found to be scaled down roughly in proportion to the isotonic load. 6. The stiffness of the muscle fibres during the isotonic shortening approached a certain finite value, when the isotonic load tended to zero. If the stiffness was measured during the development of isometric tension, the stiffness--isometric tension curve extrapolated towards the origin. 7. High-speed cinematography during the step change in load indicated a fairly uniform distribution of the series elasticity along the length of the preparation. 8. These results are discussed in relation to the sliding filament model of muscle contraction.

Animals↗

PubMed1979

Effective luminal hypotonicity: the driving force for isotonic proximal tubular fluid absorption.

This Editorial Review summarizes certain considerations relevant to the mechanism(s) of isotonic fluid absorption by the mammalian proximal nephron. Recent evidence indicates that the paracellular pathway in this epithelium has a low diffusion resistance. Therefore it is possible that lateral intercellular spaces are in diffusion equilibrium with the peritubular medium. For such a circumstance, the driving forces for isotonic fluid absorption may reside in external solutions. But since the hydraulic conductance of mammalian proximal tubules is remarkably high, the effective osmotic pressure gradient between luminal and pertibular solutions required to drive isotonic fluid transport is relatively small. In the mammalian proximal nephron, effective luminal hypotonicity may provide the driving force for isotonic fluid transport. At least two mechanisms could account for the development of effective luminal hypotonicity. First, preferential absorption of bicarbonate results in a rise of luminal Cl- concentration. And because proximal tubules are more permeable to Cl- than to HCO3-, there develops a driving force for isotonic fluid transport. Second, trivial degrees of luminal hypotonicity may develop attendant on active Na+ absorption. We provide evidence that, of these two mechanisms, axial anion asymmetry is the dominant force for isotonic fluid transport.

Absorption↗

PubMed1978

[Investigations on bloodcultures with three culture media containing Na-polyanetholsulfonate (aerobic iso- and hypertonic and anaerobic isotonic (author's transl)].

By using parallel culture techniques 330 blood specimens steming from patients of an intensive care unit were cultured simultanously in 3 media containing 0.05% Na-Poly-anetholsulfonate. Otherwise having an identical composition the media differed in the following respects : the isotonic medium A and the - by additional content of 10% sucrose - hypertonic medium B were used for aerobic culture. The anaerobic and isotonic medium C contained 2% Proteose-peptone, additionally. Without regards to the isolation of strictly anaerobic bacteria a total of 114 positive bloodcultures was obtained (tab. 1). The use of medium A resulted in 81 positive bloodcultures, that of medium B and C in 93 and 50, respectively (tab. 2). With the combined use of media A + B 103 positive bloodcultures would have been detected, with B + C 102, but with A + C 92 only (tab. 2). Of all 3 media the hypertonic medium B promotes bacterial growth most efficiently, but 13 strains grown in A did not grow in B (tab. 3), a fact that leads to the conclusion that isotonic as well as hypertonic aerobic media are employed in parallel advantageously. The effect of the hypertonic medium was expressed most distinctly with the isolation of grampositive bacteria (tab. 4). As during the period of this investigation the intensive care unit was afflicted by an outbreak of Serratia marcescens the predominance of this species among the other isolated microbes (tab. 5) is not surprising. While no difference of detection-time was observed between A and B, microbial growth in medium C seemed to be slower (fig). It was concluded that the use of 3 media, aerobic isotonic and hypertonic as well as anaerobic isotonic should be employed whenever possible.

Anaerobiosis↗

PubMed1976

Effect of cyclic nucleotides on the isotonic fluid reabsorption in the proximal convoluted tubule of rat kidney.

In order to reveal the sidedness of the cyclic AMP action on renal tubules the effect of cyclic nucleotides on isotonic fluid reabsorption was examined in proximal convoluted rat kidney tubules by using advanced micropuncture techniques. Cyclic AMP inhibited isotonic fluid reabsorption preferentially when applied on the luminal cell side. This finding coincides with a predominant distribution of a membrane bound cyclic AMP dependent protein kinase in a luminal cell membrane fraction. On the luminal cell side cyclic AMP and dibutyryl cyclic AMP inhibited isotonic fluid reabsorption in a similar dose dependent behaviour. Concentrations of both nucleotides as low as 10-10M had a definite inhibitory effect. Tested at a high concentration N6-butyryl cyclic AMP was almost as effective as cyclic AMP. Deoxy cyclic AMP, 5' AMP, cyclic GMP and dibutyryl cyclic GMP had no effect. ATP inhibited isotonic fluid reabsorption to a very small extent. The data indicate that the observed inhibition of isotonic fluid reabsorption is specific for cyclic AMP and that the interaction of cyclic AMP and the luminal cell membrane is initiated at the luminal cell surface.

Animals↗

PubMed1977

Fluid and electrolyte shifts during bed rest with isometric and isotonic exercise.

Fluid and electrolyte shifts were measured in seven men (19-21 yr) during three 2-wk bed rest (BR) periods, each of which was separated by a 3-wk ambulatory recovery period. During two of the three BR periods they performed isometric exercise and isotonic exercise. No prescribed exercise was given during the other BR period. On day 4 of BR, plasma volume decreased (P less than 0.05) 441 ml (-12.6%) with no exercise, 396 ml (-11.3%) with isometric, and 262 ml (-7.8%) with isotonic exercise; the decreases (NS) of extracellular volume were -4.4%, -2.6%, and -2.7%, respectively. By day 13 of BR, plasma volume stabilized at the lower level with isometric and isotonic exercise and continued to decline with no exercise; but the extracellular volume returned to or above control levels due to an overshoot of the interstitial volume of +320 to +430 ml (2.0-2.7%) that was about equal to the plasma volume loss. During BR there were isocontent losses from the plasma of protein, albumin, globulin, urea N2, uric acid, creatinine, Na, Cl, osmolarity, P, and glucose that were not influenced by either exercise regimen. However, the blood, red blood cell, and plasma volumes, and the Ca and K contents were stabilized during BR by both exercise regimens. The results suggest that during BR, preservation of the extracellular volume takes precedence over maintenance of the plasma volume, and this mechanism is independent of the effects of isometric or isotonic exercise.

Adult↗

PubMed1976

Isometric and isotonic length-tension relations and variaitonsin cell length in longitudinal smooth muscel from rabbit urinary bladder.

Isometric and isotonic length-tension relations of longitudinal smooth muscle from rabbit urinary bladder were studied together with muscle cell length and tissue structure as revealed histologically. In vivo strip length at a bladder volume of 10 m1 is referred to as L10. The smooth muscle was relaxed by Ca2+-free solution and contracted by K+-high solution with different Ca2+-concentrations. Maximal active force, 12.5+/-0.4 N/cm2 (S.E., n =11), for wholestrips was attained at a length of 206+/-4% (S.E., n=5) of L10. Passive tension at this length was about 15% of total tension. After correction for amount of connective tissue, maximal active tension of pure muscle bundles was 19 N/cm2. Up to about 165% of L10 isometric and isotonic length-tension relations were identical; if the muscle was stretched beyond this, it failed to shorten isotonically to the same length as when contracting from a shorter starting length. This decreased shortening capacity was reversible if the muscle was shortened passively. The extent of shortening against zero load was dependent on degree of activation suggesting an internal resistance to shortening. A linear relationship was found between bladder radius and muscle cell length, indicating that no slippage occurs between the cells when the bladder is filled. Mean cell diameter in the nuclear regionat L10 was 7.2+/-0.2 mum (S.D.,n=10). Mean macimal active tension per cell was calculated to be 2.3-10(-6) N and occurred at a cell length of 655 mum.

Animals↗

PubMed1975

Mechanism of inhibition of the proximal tubular isotonic fluid absorption by polylysine and other cationic polyamino acids.

The present study was initiated with the hope of clarifying the role of negative charges in the luminal brush border membrane in the overall process of trans-epithelial isotonic sodium and water absorption. Using micropuncture techniques, cationic polyamino acids such as polylysine (mol wt 100,000, 17,000 and 1,500-5,000, 1 mg/ml), tetralysine, polyornithine (mol wt 100,000, 1mg/ml), polyethyleneimine (2 mg/ml), polymyxin B (2 mg/ml), protamine sulfate (25 mg/ml) and histone (0.5 mg/ml) were perfused through the segments of rat kidney proximal tubule for 30 sec to 2 min. The rate of isotonic fluid absorption was measured before and after each perfusion with the Gertz's split drop method using Ringer's solution as a shrinking drop. Polylysine 100,000 and 17,000 and polyornithine were the most potent, inhibiting isotonic reabsorption by 93%. The sequence of inhibitory effect was: polylysine 100,000 congruent to polyornithine 100,000 congruent to polylysine 17,000 greater than polyethyleneimine greater than polylysine 1,500-5,000 congruent to polymyxin B greater than protamine sulfate congruent to histone. In contrast, tetralysine (2 mg/ml) showed no inhibitory effect. Electrical potential difference (p.d.) of the proximal tubular cells was destroyed within 10 sec of luminal perfusion with polylysine 100,000 (1 mg/ml). Simultaneously with the drop in p.d., electrical resistance of the luminal brush border membrane was nearly totally eliminated, whereas transepithelial input resistance remained unaltered. Furthermore, trypan blue dye was taken up by polylysine 100,000-perfused tubular cells but not by normal cells. Expanding drop analysis (mannitol solution as a split drop) was performed as a screening test to examine if the permeability for water and sodium in the lateral paracellular pathway is altered by polylysine 100,000. No significant difference was observed in the velocity of split drop expansion between untreated and polylysine-perfused tubules. A lower concentration of polylysine 100,000 (0.1 mg/ml) showed a much less inhibitory effect on fluid absorption and on cell p.d. These observations indicate that the strong inhibition on proximal tubular fluid absorption exerted by polylysine and perhaps also by other cationic polyamino acids is due not to modification of membrane negative charges but to the lysis of tubular cells by these polycations.

Animals↗

PubMed1979

Ventricular response to isometric and isotonic exercise. Echocardiographic assessment.

The effects of supine isometric handgrip and graded isotonic bicycle ergometer exercise on left ventricular performance were studied echocardiographically in 20 normal subjects, aged 18 to 36. Measurements of the left ventricular minor axis diameter were taken from recordings performed at rest, during each form of exercise, and during recovery. At the completion of isometric exercise, the pressure-rate product increased significantly. There was no significant change in percentage of fractional shortening (%deltaD), while there was a small but significant fall in peak velocity of circumferential fibre shortening (peak Vcf). Isotonic exercise resulted in a significant increase in %deltaD and peak Vcf. The pressure-rate product also increased and showed a positive correlation with peak Vcf. Isotonic exercise produced a much greater stimulus to left ventricular contractility than isometric exercise and may be a useful means of detecting latent left ventricular dysfunction echocardiographically.

Adolescent↗

PubMed1978

Volume absorption in the pars recta. III. Luminal hypotonicity as a driving force for isotonic volume absorption.

This paper examines the possibility that osmotic disequilibrium between luminal and bathing solutions may account for isotonic fluid absorption coupled to active Na+ absorption observed when superficial proximal straight tubules isolated from rabbit kidney are perfused and bathed with NaCl solutions in the absence of CO2, HCO3-, and luminal organic solutes. If luminal hypotonicity provides a driving force for isotonic fluid absorption under these conditions, the luminal fluid must be nearly isotonic; and steady-state luminal hypotonicity should develop sufficiently rapidly that the absolute rate of volume absorption ('JV, nl min-1) coupled to active Na+ transport is relatively independent of perfusion rate, so that the normalized rate of fluid absorption (JV, nl min-1 mm-1) is approximately constant. Our theoretical calculations indicate that these expectations are fulfilled. A 0.42-0.56 mM reduction in luminal NaCl concentration adequately accounts for the JV observed under such conditions, because of the high hydraulic conductivity of these tubules; and within the range of tubule lengths normally employed with isolated proximal straight tubules, JV is relatively indepedent of perfusion rate within the generally observed range of experimental error.

Absorption↗

PubMed1977

Insulin and glucose responses during bed rest with isotonic and isometric exercise.

The effects of daily intensive isotonic (68% maximum oxygen uptake (VO2 max)) and isometric (21% maximum extension force) leg exercise on plasma insulin and glucose responses to an oral glucose tolerance test (OGTT) during 14-day bed-rest (BR) periods were investigated in seven young healthy men. The OGTT was given during ambulatory control and on day 10 of the no-exercise, isotonic, and isometric exercise BR periods during the 15-wk study. The subjects were placed on a controlled diet (mean +/- SD = 344 +/- 34 g CHO/day and 3,073 +/- 155 (SD) kcal/day) starting 10 days before each BR period. During BR, basal plasma glucose concentration remained unchanged with no exercise, but increased (P less than 0.05) to 87-89 mg/100 ml with both exercise regimens on day 2, and then fell slightly below control levels on day 13. The fall of glucose content (-11 to -15%) during BR was independent of the exercise regimen and was an adjustment for the loss of plasma vol. The intensity of the response of insulin and glucose to the OGTT (integrated area under the curves) was inversely proportional to the total daily energy expenditure during BR; i.e., the largest response with no exercise, then isometric, isotonic, and ambulatory exercise. It was estimated that at least 1,020 kcal/day must be provided by supplemental exercise to restore the hyperinsulinemia to control levels.

Adult↗

PubMed1977

H+ translocation in lysozyme-treated cells of the blue-green alga Plectonema boryanum. Difference between isotonically and hypotonically treated preparations and effects of divalent cations.

Lysozyme-treated cells of a blue-green alga, Plectonema boryanum, had an internal pH of 7.3+/-0.2 under isotonic and hypotonic conditions. This value was similar to that of untreated cells. The CCCP-induced biphasic H+ change seen in the isotonic cells was not observed in the hypotonically treated cells. The biphasic time course remained in the hypotonic preparation if CaCl2 or MgCl2 was added prior to the osmotic shock. It is suggested that the cells have two compartments of H+ concentration. The outer region may be more acidic than the inner region. A light-induced H+ efflux was observed under isotonic conditions and an influx of H+ under hypotonic conditions. The H+ influx was not observed when lysozyme-treated cells were incubated with CaCl2 or MgCl2 prior to the hypotonic treatment. Two types of effects of divalent cations, one on the rigidity of the outer membrane and another on the permeability characteristics of the inner photosynthetic membrane, are indicated. Rearrangement of the photosynthetic membranes and an apparent inversion of the H+ pump by hypotonic shock are also suggested.

Biological Transport, Active↗

PubMed1978

Tissue osmolality in intestinal villi during luminal perfusion with isotonic electrolyte solutions.

A cryoscoptic technique has been developed that makes it possible to determine tissue osmolality in the core of the intestinal villi. During absorption from an isotonic electrolyte solution containing glucose an osmolality gradient was demonstrated from tip to base of the villi in both the jejunum and the ileum. The tissue osmolality at the villous tips was measured to 1 000-1 200 mOsm/kg H2O while the osmolality at the villous base was approximately isotonic with plasma. Increasing intestinal blood flow by i.a. administration of a vasodilator drug, or making the intestine ischemic by clamping the intestinal vascular supply while supplying the mucosa with oxygen, markedly decreased tissue osmolality. Substituting all sodium ions with choline in the luminal perfusate abolished almost completely the tissue hyperosmolality and the intestine became a secretory organ. These observations are consistent with the view that the observed villous tissue hyperosmolality was created by a countercurrent multiplication of sodium chloride. The physiological implications of this mechanism is discussed and it is, among other things, proposed that the hyperosmolar region represents the hyperosmotic compartment necessary for explaining intestinal water absorption.

Animals↗

PubMed1976

The effect of SO24-, NO-3, Ca2+ and temperature upon sodium-free contracture, isotonic and isometric contraction of the isolated rat right ventricle.

Sodium-free contracture was directly dependent on the presence of Ca2+ in Tyrode sulphate solution. The first phase of contracture increased in Tyrode nitrate solution more quickly than in sulphate solution, while the second phase was the same. Higher amplitude of isotonic contractions was observed on substituting nitrates for chlorides in the Tyrode solution than in sulphate substitution. In Tyrode sulphate solution, spontaneous contractions appeared in 50% of the experiments. The relationship between the duration and tension of isotonic contraction, given the same pre-loading, showed greater diminution of the contractions, at the lower temperature (22 degrees C) than at the higher temperature (35 degrees C), whereas passive stretching of the muscle was not influenced by the temperature. Isometric contrations lasted longer at the lower temperature. The amphlitude of isometric contractions was directly correlated to the frequency of electrical stimulation at a constant temperature (22 degrees C). The results showed that shifts of the calcium participating in contraction of the rat ventricle are influenced both by the anion and cation content of the medium and by its temperature.

Animals↗

PubMed1978

[Participation of Na, K-ATPase in the mechanism of isotonic fluid absorption by the epithelium of the frog gallbladder].

In experiments on the isolated frog gallbladders it was shown that addition of ouabain (1.10(-4) M) or noradrenaline 3.10(-6) M) into the incubation Ringer solution from the serous surface of the gallbladder and also replacement of K+ in the solution for the equivalent quantity of Na+ ions caused a reduction of the absorption of isotonic fluid by the epithelium and a fall of the Na,K-ATPase activity in its cells. Noradrenaline also cased a reduction of Mg-ATPase activity. A significant positive correlation was found between the transport rate of the isotonic fluid by the epithelium and the Na,K-ATPase activity in its cells.

Absorption↗

PubMed1976

Membrane studies of Streptococcus pyogenes and its L-form growing in hypertonic and physiologically isotonic media. An electron spin resonance spectroscopy approach.

Electron spin resonance spectroscopy (ESR) was used to compare the lipid organization, thermal stability and the physical state of the membrane of a human pathogen, Streptococcus pyogenes and its osmotically fragile L-form with this same L-form now adapted to grow under physiologically isotonic conditions (physiological L-form). Comparison of the hyperfine splittings of a derivative of 5-ketostearic acid spin label, I(12, 3), after incorporation into the membrane, revealed that the lipid chain rigidity of these membranes is in the order physiological L-form greater than osmotically fragile L-form greater than streptococcus. The signal intensity (of the center magnetic field line) versus temperature analysis showed two transitions for these membranes. The first with melting points of 45, 26 and 36 degrees C and second transition at 70, 63 and 60 degrees C for the physiological L-form, osmotically fragile L-form and streptococcal membranes, respectively. This same order of membrane lipid chain rigidity was seen from the cooperativities obtained for each of these systems from analysis based on the expression for an n-order reaction. The I(12, 3) and other probes with the paramagnetic group close to the methyl end of the molecule suggested that this difference in lipid chain rigidity between these organisms resides in the environment closer to the lipid head group region rather than in the hydrophobic lipid core. Another major finding was the binding of I(12, 3) at two or more different sites in each of the membranes examined. This change in lipid chain rigidity now provides an explanation to account for the survival of a previously osmotically fragile L-form in physiologically isotonic media by focusing on changes in the physical nature of its membrane. In so doing, it adds to and reinforces the speculation of the potential survival in vivo and involvement in pathogenesis of osmotically fragile aberrant forms of bacteria.

Cell Membrane↗

PubMed1978

A laterality effect in isometric and isotonic labial tracking.

Hemispheric dominance for sensorimotor control of lip activity was investigated by use of a pursuit auditory tracking task. This task involves continuous frequency matching of a computer-generated target tone and a subject-controlled cursor tone. Thirty right-handed subjects were tested under isometric lip and hand control, and 20 right-handed subjects under isotonic lip control. Subjects tracked 10 1-min trials under each laterality condition--cursor/right ear, target/left ear, and vice versa. In both experiments tracking performance was better when the lip-controlled cursor tone was presented to the right ear (hence direct contralateral route to left hemisphere). A significant (p less than 0.05) cursor/right-ear advantage was found under isometric hand-tracking. Analysis routines examined relative laterality advantages across several time intervals within each 1-min trial. Consistent lateralization scores in favor of cursor/right-ear presentations (REAs) were independent of the time interval measured. For isometric tracking, 58% of subjects having laterality advantages (p less than 0.10) revealed REAs. For isotonic tracking, 71% of subjects revealed REAs. Implications of the latter finding are discussed relative to a left hemisphere mechanism specialized to integrate movement-generated auditory feedback with dynamic kinesthetic information from the articulators.

Adolescent↗

PubMed1979

Indices of myocardial oxygen consumption for isotonic contraction.

To investigate the model-independent mechanical determinants of energy expenditure, a respirometer was constructed to study isolated feline papillary muscles. Mechanical parameters recorded were the distance of shortening (deltaL), peak velocity of shortening (Vp), mean velocity of shortening (V), tension-time index (TTI), afterload (P), and the integral of the contraction portion of the phase plane trajectory of velocity and length (integral of VdL). Oxygen consumption (Vo2) during 15-min isotonic contraction periods was monitored with a polarographic electrode. Vp, V, and delta L were inversely related to Vo2 in a curvilinear manner. P and TTI were directly related to Vo2 in a curvilinear fashion. Integral of VdL was inversely related to Vo2 in a linear manner. In several experiments the contractile state of the muscles was augmented by addition of norepinephrine (7 X 10(-8) M). The relationship between integral of VdL and Vo2 was shifted above and parallel to that for the control muscles. These experiments indicate that the index integral of VdL is linearly related to the oxygen consumed in isotonic contraction of isolated mammalian ventricular myocardium at a given level of contractile state.

Animals↗

PubMedDate not supplied

Preparation of human erythrocyte ghosts in isotonic solution: haemoglobin content and polypeptide composition.

Human red blood cell ghosts were prepared by dielectric breakdown of the cell membrane and subsequent electrical haemolysis in isotonic and isoionic solutions. Almost complete removal of haemoglobin (to about 0.1%) could be achieved by subjecting the erythrocytes suspended in isotonic solution to three consecutive electric field pulses of 16 kV/cm in the presence of 10 mM EDTA, followed by dilution with EDTA-free isoionic medium. The cup-shaped ghost cells were electrically homogeneous. The polypeptide composition of the electrically prepared ghost cells, as analyzed by polyacrylamide electrophoresis in 1% SDS, revealed a pattern similar to ghost cells prepared by osmotic haemolysis. However, the band 6, corresponding to glyceraldehyde-3-phosphate-dehydrogenase protomer, was absent from the electrically prepared ghost cells. Also the band 8, which is eluted at low ionic strength, appeared to be very prominent in the electrical preparations.

Cell Fractionation↗