scholarly journals Nonparallel isometric tension response of rabbit soleus skinned muscle fibers to magnesium adenosine triphosphate and magnesium inosine triphosphate.

1979 ◽  
Vol 74 (2) ◽  
pp. 261-274 ◽  
Author(s):  
B Krasner
Keyword(s):  
Steady State ◽  
Ionic Strength ◽  
Adenosine Triphosphate ◽  
Soleus Muscle ◽  
Muscle Fibers ◽  
Isometric Tension ◽  
Maximum Tension ◽  
Skinned Muscle ◽  
Tension Response ◽  
Skinned Muscle Fibers

The isometric tension response of single "skinned' rabbit soleus muscle fibers to MgATP and McITP in the absence of calcium was studied. [MgATP] or [MgITP] was varied in solutions of ionic strength 0.30 and temperature 20 degrees C. Steady-state tension that developed in MgATP or MgITP solutions was a biphasic bell-shaped function of log [MgATP] or log [MgITP] which increased from zero to maximum tension and then declined again to zero. Analysis of the data showed that, under comparable ionic conditions, percent tension vs. log [MgATP] and percent tension vs. log [MgITP] curves are not parallel. Instead, the percent tension vs. log [MgITP] curve is much broader. Additionally, under comparable ionic conditions maximum tension in MgITP solutions was higher than in MgATP solutions. In addition, in MgATP solutions, pH, [K+], and excess ATP were varied. Raising pH from 7 to 8, [K+] from 46 mM to 200 mM, or decreasing excess ATP from 2 to 0.5 mM all increased maximum tension. None of these factors, however, influenced the shape or position of the percent tension vs. log [MgATP] curve.

scholarly journals Tension in Skinned Frog Muscle Fibers in Solutions of Varying Ionic Strength and Neutral Salt Composition

1973 ◽  
Vol 62 (5) ◽  
pp. 550-574 ◽  
Author(s):  
A. M. Gordon ◽  
R. E. Godt ◽  
S. K. B. Donaldson ◽  
C. E. Harris
Keyword(s):  
Ionic Strength ◽  
Muscle Fiber ◽  
Muscle Fibers ◽  
Isometric Tension ◽  
High Ionic Strength ◽  
Frog Muscle ◽  
Hypertonic Solution ◽  
Base Line ◽  
Neutral Salt ◽  
Skinned Muscle

The maximal calcium-activated isometric tension produced by a skinned frog single muscle fiber falls off as the ionic strength of the solution bathing this fiber is elevated declining to zero near 0.5 M as the ionic strength is varied using KCl. When other neutral salts are used, the tension always declines at high ionic strength, but there is some difference between the various neutral salts used. The anions and cations can be ordered in terms of their ability to inhibit the maximal calcium-activated tension. The order of increasing inhibition of tension (decreasing tension) at high ionic strength for anions is propionate- ≃ SO4-- < Cl- < Br-. The order of increasing inhibition of calcium-activated tension for cations is K+ ≃ Na+ ≃ TMA+ < TEA+ < TPrA+ < TBuA+. The decline of maximal calcium-activated isometric tension with elevated salt concentration (ionic strength) can quantitatively explain the decline of isometric tetanic tension of a frog muscle fiber bathed in a hypertonic solution if one assumes that the internal ionic strength of a muscle fiber in normal Ringer's solution is 0.14–0.17 M. There is an increase in the base-line tension of a skinned muscle fiber bathed in a relaxing solution (no added calcium and 3 mM EGTA) of low ionic strength. This tension, which has no correlate in the intact fiber in hypotonic solutions, appears to be a noncalcium-activated tension and correlates more with a declining ionic strength than with small changes in [MgATP], [Mg], pH buffer, or [EGTA]. It is dependent upon the specific neutral salts used with cations being ordered in increasing inhibition of this noncalcium-activated tension (decreasing tension) as TPrA+ < TMA+ < K+ ≃ Na+. Measurements of potentials inside these skinned muscle fibers bathed in relaxing solutions produced occasional small positive values (<6 mV) which were not significantly different from zero.

scholarly journals Excitation of skinned muscle fibers by imposed ion gradients. I. Stimulation of 45Ca efflux at constant [K][Cl] product.

1985 ◽  
Vol 86 (6) ◽  
pp. 813-832 ◽  
Author(s):  
E W Stephenson
Keyword(s):  
Isometric Force ◽  
Muscle Fibers ◽  
Water Flux ◽  
Skinned Muscle ◽  
Skinned Muscle Fibers ◽  
Diffusion Potentials ◽  
45Ca Efflux ◽  
Osmotic Effects ◽  
45Ca Release ◽  
And Diffusion

45Ca efflux from skinned muscle fibers is stimulated transiently, by a highly Ca2+-dependent mechanism, by KCl replacement of K propionate. In the present studies, Cl replaced the much less permeant anion methanesulfonate (Mes) either (a) at constant [K], in which increased [K][Cl] permits net KCl and water flux across internal membranes, or (b) at constant [K][Cl] (choline substitution), in which the imposed gradients and diffusion potentials should dissipate slowly. 45Ca efflux and isometric force were measured simultaneously on segments of frog semitendinosus fibers skinned by microdissection. EGTA was applied to chelate released 45Ca either (a) shortly after high [Cl] (interrupted response), to minimize reaccumulation, (b) before high [Cl] (pretreated response), to evaluate Ca2+ dependence, or (c) under control conditions in KMes. KCl replacement of KMes stimulated release of 65% fiber 45Ca within 1 min in interrupted responses; EGTA pretreatment was only moderately inhibitory with substantial residual stimulation. In contrast, choline Cl replacement of KMes induced release of 26-35% fiber 45Ca in interrupted responses; EGTA pretreatment was strongly inhibitory, but release significantly exceeded control with a small, sustained increase in Ca2+-insensitive efflux. These differences in 45Ca release and EGTA inhibition suggest that Cl replacement of Mes at constant [K] stimulates efflux by osmotic effects as well as imposed diffusion potentials; at least half the stimulated 45Ca loss (above control) in interrupted KCl responses is attributable to an osmotic component with low Ca2+ sensitivity. In the highly Ca2+-sensitive stimulation at constant [K][Cl], 45Ca release (above control) in interrupted responses correlated well with that in the pretreated responses of segments from the same fiber, with a slope of 8.4. This relationship suggests that imposed diffusion potentials stimulate a small Ca2+-insensitive component that gradates a much larger Ca2+-dependent efflux. The Ca2+-insensitive component apparently reflects intermediate steps in the excitation-contraction coupling that require positive feedback to result in sufficient Ca release for contraction.

Enhancement of Ca2+-induced Ca2+ release in calpain treated rabbit skinned muscle fibers

1992 ◽  
Vol 185 (2) ◽  
pp. 713-718 ◽  
Author(s):  
Masamitsu Iino ◽  
Hiromi Takano-Ohmuro ◽  
Yoko Kawana ◽  
Makoto Endo
Keyword(s):  
Muscle Fibers ◽  
Skinned Muscle ◽  
Skinned Muscle Fibers
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