Frequency‐dependent lipid raft uptake at rat diaphragm muscle axon terminals

Van Balkom, Roland H. H., Wen-Zhi Zhan, Y. S. Prakash, P. N. Richard Dekhuijzen, and Gary C. Sieck. Corticosteroid effects on isotonic contractile properties of rat diaphragm muscle. J. Appl. Physiol. 83(4): 1062–1067, 1997.—The effects of corticosteroids (CS) on diaphragm muscle (Diam) fiber morphology and contractile properties were evaluated in three groups of rats: controls (Ctl), surgical sham and weight-matched controls (Sham), and CS-treated (6 mg ⋅ kg−1 ⋅ day−1prednisolone at 2.5 ml/h for 3 wk). In the CS-treated Diam, there was a selective atrophy of type IIx and IIb fibers, compared with a generalized atrophy of all fibers in the Sham group. Maximum isometric force was reduced by 20% in the CS group compared with both Ctl and Sham. Maximum shortening velocity in the CS Diamwas slowed by ∼20% compared with Ctl and Sham. Peak power output of the CS Diam was only 60% of Ctl and 70% of Sham. Endurance to repeated isotonic contractions improved in the CS-treated Diam compared with Ctl. We conclude that the atrophy of type IIx and IIb fibers in the Diam can only partially account for the CS-induced changes in isotonic contractile properties. Other factors such as reduced myofibrillar density or altered cross-bridge cycling kinetics are also likely to contribute to the effects of CS treatment.

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Interstitial space and collagen alterations of the developing rat diaphragm

Journal of Applied Physiology ◽

10.1152/jappl.1993.74.5.2450 ◽

1993 ◽

Vol 74 (5) ◽

pp. 2450-2455 ◽

Cited By ~ 10

Author(s):

L. E. Gosselin ◽

D. A. Martinez ◽

A. C. Vailas ◽

G. C. Sieck

Keyword(s):

Postnatal Growth ◽

Interstitial Space ◽

Collagen Content ◽

Diaphragm Muscle ◽

Adult Males ◽

Rat Diaphragm ◽

Collagen Concentration ◽

Cross Sectional ◽

Hydroxyproline Concentration ◽

Total Muscle

The effect of growth on the relative interstitial space [%total cross-sectional area (CSA)] and collagen content of the rat diaphragm muscle was examined at postnatal ages of 0, 7, 14, and 21 days as well as in adult males. The proportion of interstitial space relative to total muscle CSA was determined by computerized image analysis of lectin-stained cross sections of diaphragm muscle. To assess collagen content and extent of collagen maturation (i.e., cross-linking), high-pressure liquid chromatography analysis was used to measure hydroxyproline concentration and the nonreducible collagen cross-link hydroxylysylpyridinoline (HP), respectively. At birth, interstitial space accounted for approximately 47% of total diaphragm muscle CSA. During postnatal growth, the relative contribution of interstitial space decreased such that by adulthood the interstitial space accounted for approximately 18% of total muscle CSA. The change in relative interstitial space occurred without a concomitant change in hydroxyproline concentration. However, the concentration of HP markedly increased with age such that the adult diaphragm contained approximately 17 times more HP than at birth. These results indicate that during development the relative CSA occupied by interstitial space decreases as muscle fiber size increases. However, the reduction in relative interstitial space is not associated with a change in collagen concentration. Thus collagen density in the interstitial space may increase with age. It is possible that the observed changes in relative interstitial space and collagen influence the passive length-force properties of the diaphragm.

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Intracellular pH transients in rat diaphragm muscle measured with DMO

AJP Cell Physiology ◽

10.1152/ajpcell.1978.235.1.c49 ◽

1978 ◽

Vol 235 (1) ◽

pp. C49-C54 ◽

Cited By ~ 16

Author(s):

A. Roos ◽

W. F. Boron

Keyword(s):

Intracellular Ph ◽

Weak Acid ◽

Diaphragm Muscle ◽

Disulfonic Acid ◽

Free Solution ◽

Rat Diaphragm ◽

Control Value ◽

Acid Load ◽

Acid Extrusion ◽

Acid Loading

Changes of the intracellular pH of rat diaphragm muscle were monitored at 30-min intervals with the weak acid DMO (5,5-dimethyl-2,4-oxazolidinedione). Transferring the muscle from a CO2-containing to a CO2-free solution caused intracellular pH (pHi) to rise by an average of 0.18 during the first 30 min and then to level off at a slightly lower value over the next 60-90 min. Transferring the muscle from a CO2-free to a CO2-containing solution caused pHi to fall by 0.18 during the first 30 min and then to recover by 0.05 over the next 90 min. Subsequent return to the CO2-free solution caused pHi to overshoot the control value by 0.10. Both the recovery and the overshoot can be accounted for by an acid-extruding pump. Intracellular acid loading with 118 mM DMO similarly caused pHi to fall initially, to recover slowly during the acid loading, and then to overshoot the control pHi on removal of the acid load. In the absence of HCO3-/CO2, acid extrusion was reduced by about a fifth. SITS (4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid) had no effect. The absence of either Na+ or Cl- from HCO3-/CO2- free solution reduced acid extrusion by about a half.

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Chlormadinone acetate, a progesterone derivative that binds to the digitalis receptor, inhibits the sodium pump in the isolated rat diaphragm

Canadian Journal of Physiology and Pharmacology ◽

10.1139/y85-007 ◽

1985 ◽

Vol 63 (1) ◽

pp. 44-47 ◽

Cited By ~ 3

Author(s):

Ivan Bihler ◽

Frank S. LaBella ◽

P. C. Sawh

Keyword(s):

Sodium Pump ◽

Sugar Transport ◽

Diaphragm Muscle ◽

Rat Diaphragm ◽

Bathing Medium ◽

Chlormadinone Acetate ◽

Muscle Tissues ◽

Pump Activity ◽

Intact Muscle ◽

Resting Muscle

Rb+ uptake, intracellular Na+ and K+ levels, and the tissue–medium distribution of the nonmetabolized glucose analog, 3-O-methyl-D-glucose (3-MG) were measured in rat diaphragms incubated with chiormadinone acetate, 6-chloro-4,6-pregnadien-17-ol-3,20-dione 17-acetate (CMA), in the presence and absence of ouabain. CMA in concentrations of 5 × 10−7 M or higher significantly depressed 86Rb uptake, and promoted an increase in internal Na+ and a decrease in internal K+, indicating inhibition of the sodium pump. Sugar transport in resting muscle parallels the changes in internal Na+ levels and is an additional indicator of sodium pump activity. Equilibration of 3-MG between tissue and medium was accelerated by CMA, in parallel to the rise in internal Na+ level. Effects of CMA on Na+ levels and sugar transport, but not on Rb+ uptake, were additive to those of various concentrations of ouabain, suggesting interaction with sites not affected by ouabain. These results on diaphragm muscle confirm our previous studies on isolated cardiac muscle preparations showing that CMA, added to the aqueous bathing medium, inhibits the sodium pump in intact muscle tissues.

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Effect of unilateral denervation on maximum specific force in rat diaphragm muscle fibers

Journal of Applied Physiology ◽

10.1152/jappl.2001.90.4.1196 ◽

2001 ◽

Vol 90 (4) ◽

pp. 1196-1204 ◽

Cited By ~ 48

Author(s):

Paige C. Geiger ◽

Mark J. Cody ◽

Rebecca L. Macken ◽

Megan E. Bayrd ◽

Gary C. Sieck

Keyword(s):

Diaphragm Muscle ◽

Specific Force ◽

Rat Diaphragm ◽

Standard Curve ◽

Fast Myosin ◽

Sds Page ◽

Fast Myosin Heavy Chain ◽

Cross Bridges ◽

Triton X ◽

Permeabilized Fibers

We hypothesize that 1) the effect of denervation (DNV) is more pronounced in fibers expressing fast myosin heavy chain (MHC) isoforms and 2) the effect of DNV on maximum specific force reflects a reduction in MHC content per half sarcomere or the number of cross bridges in parallel. Studies were performed on single Triton X-100-permeabilized fibers activated at a pCa (−log Ca2+ concentration) of 4.0. MHC content per half sarcomere was determined by densitometric analysis of SDS-PAGE gels and comparison to a standard curve of known MHC concentrations. After 2 of wk DNV, the maximum specific force of fibers expressing MHC2X was reduced by ∼40% (MHC2Bexpression was absent), whereas the maximum specific force of fibers expressing MHC2A and MHCslow decreased by only ∼20%. DNV also reduced the MHC content in fibers expressing MHC2X, with no effect on fibers expressing MHC2A and MHCslow. When normalized for MHC content per half sarcomere, force generated by DNV fibers expressing MHC2X and MHC2A was decreased compared with control fibers. These results suggest the force per cross bridge is also affected by DNV.

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Power fatigue of the rat diaphragm muscle

Journal of Applied Physiology ◽

10.1152/jappl.2000.89.6.2215 ◽

2000 ◽

Vol 89 (6) ◽

pp. 2215-2219 ◽

Cited By ~ 23

Author(s):

Bill T. Ameredes ◽

Wen-Zhi Zhan ◽

Y. S. Prakash ◽

Rene Vandenboom ◽

Gary C. Sieck

Keyword(s):

Diaphragm Muscle ◽

Fiber Types ◽

Rat Diaphragm ◽

Shortening Velocity ◽

Reduction In Force ◽

Novel Technique ◽

Velocity Relationship ◽

Stimulus Train ◽

Force Velocity

We hypothesized that decrements in maximum power output (W˙max) of the rat diaphragm (Dia) muscle with repetitive activation are due to a disproportionate reduction in force (force fatigue) compared with a slowing of shortening velocity (velocity fatigue). Segments of midcostal Dia muscle were mounted in vitro (26°C) and stimulated directly at 75 Hz in 400-ms-duration trains repeated each second (duty cycle = 0.4) for 120 s. A novel technique was used to monitor instantaneous reductions in maximum specific force (Po) andW˙max during fatigue. During each stimulus train, activation was isometric for the initial 360 ms during which Po was measured; the muscle was then allowed to shorten at a constant velocity (30% V max) for the final 40 ms, and W˙max was determined. Compared with initial values, after 120 s of repetitive activation, Po andW˙max decreased by 75 and 73%, respectively. Maximum shortening velocity was measured in two ways: by extrapolation of the force-velocity relationship ( V max) and using the slack test [maximum unloaded shortening velocity ( V o)]. After 120 s of repetitive activation, V max slowed by 44%, whereas V o slowed by 22%. Thus the decrease inW˙max with repetitive activation was dominated by force fatigue, with velocity fatigue playing a secondary role. On the basis of a greater slowing of V max vs. V o, we also conclude that force and power fatigue cannot be attributed simply to the total inactivation of the most fatigable fiber types.

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THE WATER AND ELECTROLYTE METABOLISM OF RAT DIAPHRAGM IN VITRO

Canadian Journal of Biochemistry and Physiology ◽

10.1139/y56-110 ◽

1956 ◽

Vol 34 (1) ◽

pp. 1069-1083 ◽

Cited By ~ 1

Author(s):

R. H. Rixon ◽

J. A. F. Stevenson

Keyword(s):

Intracellular Water ◽

Diaphragm Muscle ◽

Optimal Conditions ◽

Rat Diaphragm ◽

Concentration Gradients ◽

Hypoxic Conditions ◽

Diaphragm In Vitro ◽

Sodium And Potassium

The distribution of water and of sodium and potassium between the cell and synthetic environments has been studied in rat diaphragm muscle. It has been found that: (1) the amount of intracellular water is markedly increased at 0 °C. in oxygen and at 37 °C. in nitrogen compared to that of tissue at 37 °C. in oxygen, in media up to 0.75 osmolar; (2) optimal conditions of temperature and oxygen are necessary to prevent or reduce the uptake of water; (3) swelling at reduced temperatures and under hypoxic conditions is related to the oxygen uptake; (4) the loss of tissue solids during incubation does not have any significant effect on the calculation of the total tissue and intracellular water; (5) the concentration of total sodium and potassium in the tissue, in vivo and in vitro at optimal conditions is slightly in excess of that in the plasma water or incubating medium—this is believed not to represent an active hypertonicity; (6) concomitant with the uptake of water there are marked redistributions of sodium and potassium, the gain of sodium being greater than the loss of potassium. It is concluded that the swelling of tissue cells under conditions that inhibit oxidative metabolism is primarily due to the redistribution of electrolytes and that the natural distribution of water in muscle is determined by active maintenance of the concentration gradients of sodium and potassium across the cell membrane.

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Isotonic contractile and fatigue properties of developing rat diaphragm muscle

Journal of Applied Physiology ◽

10.1152/jappl.1998.84.4.1260 ◽

1998 ◽

Vol 84 (4) ◽

pp. 1260-1268 ◽

Cited By ~ 37

Author(s):

Wen-Zhi Zhan ◽

Jon F. Watchko ◽

Y. S. Prakash ◽

Gary C. Sieck

Keyword(s):

Power Output ◽

Supply And Demand ◽

Maximum Power ◽

Diaphragm Muscle ◽

Fatigue Properties ◽

Rat Diaphragm ◽

Shortening Velocity ◽

Endurance Time ◽

Early Postnatal Development ◽

Maximum Power Output

Postnatal transitions in myosin heavy chain (MHC) isoform expression were found to be associated with changes in both isometric and isotonic contractile properties of rat diaphragm muscle (Diam). Expression of MHCneo predominated in neonatal Diam fibers but was usually coexpressed with MHCslow or MHC2A isoforms. Expression of MHCneo disappeared by day 28. Expression of MHC2X and MHC2B emerged at day 14 and increased thereafter. Associated with these MHC transitions in the Diam, maximum isometric tetanic force (Po), maximum shortening velocity, and maximum power output progressively increased during early postnatal development. Maximum power output of the Diam occurred at ∼40% Po at days 0 and 7 and at ∼30% Po in older animals. Susceptibility to isometric and isotonic fatigue, defined as a decline in force and power output during repetitive activation, respectively, increased with maturation. Isotonic endurance time, defined as the time for maximum power output to decline to zero, progressively decreased with maturation. In contrast, isometric endurance time, defined as the time for force to decline to 30–40% Po, remained >300 s until after day 28. We speculate that with the postnatal transition to MHC2X and MHC2Bexpression energy requirements for contraction increase, especially during isotonic shortening, leading to a greater imbalance between energy supply and demand.

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