Mechanical characteristics of chemically skinned guinea-pig taenia coli

Strips of intact and chemically skinned (Triton X-100) taenia coli were mounted for isometric and quick-release experiments at 23 degrees 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 at pCa = 5.62 +/- 0.4 and a maximal force (63 +/- 8 mN/mm2) at pCa = 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 (Vmax) 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 in Vmax was found when the Ca2+ concentration was reduced. Calmodulin (1 microM) increased Ca2+ sensitivity (by about 0.6 log units) of the skinned preparation but at optimal Ca2+ caused no alteration in isometric force or Vmax.