EFFECT OF HINDLIMB UNLOADING ON RAT SOLEUS FIBER FORCE, STIFFNESS, AND CALCIUM SENSITIVITY

被引:83
作者
MCDONALD, KS [1 ]
FITTS, RH [1 ]
机构
[1] MARQUETTE UNIV,DEPT BIOL,MILWAUKEE,WI 53201
关键词
MODELS OF WEIGHTLESSNESS; SINGLE-FIBER FUNCTION;
D O I
10.1152/jappl.1995.79.5.1796
中图分类号
Q4 [生理学];
学科分类号
071003 ;
摘要
The purpose of this study was to examine the time course of change in soleus muscle fiber peak force (N), tension (P-o, KN/m(2)), elastic modulus (E(o)), and force-pCa and stiffness-pCa relationships. After 1, 2, or 3 wk of hindlimb unloading (HU), single fibers were isolated and placed between a motor arm and a transducer, and fiber diameter, peak absolute force, Po-,Po- E(o), and force-pCa and stiffness-pCa relationships were characterized. One week of HU resulted in a significant reduction in fiber diameter (68 +/- 2 vs. 57 +/- 1 mu m), force (3.59 +/- 0.15 vs. 2.19 +/- 0.12 x 10(-4) N), P-o (102 +/- 4 vs. 85 +/- 2 kN/ m(2)), and E(o) (1.96 +/- 0.12 vs. 1.37 +/- 0.13 x 10(7) N/m(2)), and 2 wk of HU caused a further decline in fiber diameter (45 +/- 1 mu m), force (1.31 +/- 0.06 x 10(-4) N), and E(o) (0.96 +/- 0.09 x 10(7) N/m(2)). Although the mean fiber diameter and absolute force continued to decline through 3 wk of HU, P-o recovered to values not significantly different from control. The P-o/E(o) ratio was significantly increased after 1 (5.5 +/- 0.3 to 7.1 +/- 0.6), 2, and 3 wk of HU, and the 2-wk (9.5 +/- 0.4) and 3-wk (9.4 +/- 0.8) values were significantly greater than the 1-wk values. The force-pCa and stiffness-pCa curves were shifted rightward after 1, 2, and 3 wk of HU. At 1 wk of HU, the Ca2+ sensitivity of isometric force, assessed by Ca2+ concentration required for half-maximal force, was increased from the control value of 1.83 +/- 0.12 to 2.30 +/- 0.10 mu M. In conclusion, after HU, the decrease in soleus fiber P-o can be explained by a reduction in the number of myofibrillar cross bridges per cross-sectional area. Our working hypothesis is that the loss of contractile protein reduces the number of cross bridges per cross-sectional area and increases the filament lattice spacing. The increased spacing reduces cross-bridge force and stiffness, but P-o/E(o) increases because of a quantitatively greater effect on stiffness.
引用
收藏
页码:1796 / 1802
页数:7
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