Mechanical characteristics of chemically skinned guinea-pig taenia coli

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Abstract
Strips of intact and chemically skinned (Triton X-100) taenia coli were mounted for isometric and quick-release experiments at 23°C. Active force increased in repeated high-K+ induced contractures in the intact muscle. Stable maximal force was 313±24 mN/mm2 (n=6). The skinned preparations activated by Ca2+, at 2 mM Mg2+, 3.2 mM MgATP and ionic strength 0.085 M, gave half maximal force atpCa=5.62±0.4 and a maximal force (63±8 mN/mm2) atpCa=4.5 (20–25 of the control K+-responses prior to skinning but about 60% of the first K+-response). Force-velocity relations were obtained from intact muscles and from the same muscles chemically skinned and activated at optimal Ca2+. Maximal shortening velocity (V max) was unaltered in the skinned preparation compared to the intact muscle (0.138±0.011 vs 0.140±0.006 L/s) indicating similar kinetics of actomyosin interaction. In the intact muscle a decrease inV max was found when the Ca2+ concentration was reduced. Calmodulin (1μM) increased Ca2+ sensitivity (by about 0.6 log units) of the skinned preparation but at optimal Ca2+ caused no alteration in isometric force orV max