Gründeman R L, de Beer E L, van den Berg C, van Buuren K J, Schiereck P
Department of Medical Physiology, University of Utrecht, The Netherlands.
Am J Physiol. 1991 Mar;260(3 Pt 1):C609-17. doi: 10.1152/ajpcell.1991.260.3.C609.
Over a wide range of sarcomere lengths, force activation by Ca2+, Ba2+, and Sr2+ was studied in papillary muscle and in fast skeletal fibers of the gracilis muscle of the rabbit, both skinned by means of freeze drying. The length-tension relations of Ba2+ activation differ significantly from those of Sr2+ and Ca2+ activation with respect to both the value and the position of the maximum. At (almost) full activation, force induced in gracilis muscle by Ba2+ was 50% of the developed force induced by Ca2+. The position of the Sr2+ sensitivity curve for papillary muscle preparations is independent of sarcomere length, in contrast to the position of the Ca2+ sensitivity curves. The binding of Sr2+ to the papillary preparation proves to be very stable as observed from the long-lasting relaxation after activation. Immersion of the papillary preparation in the relaxation fluid after activation with Ba2+ results in a tension transient: a rise in tension followed by a decrease was observed. The maximal value of the tension transient was up to twice the steady tension, dependent on Ba2+ concentration. The steady-state tension was approximately 50% of the Ca2(+)-induced tension. Ba2+ sensitivity curves are not sigmoidal but show a maximum. Above [Ba2+] greater than 10(-5) to 10(-4) M (dependent on sarcomere length) tension decreased. These observations suggest that two counteracting processes govern Ba2+ contraction in papillary muscle preparations, namely activation and inhibition.
在很宽的肌节长度范围内，研究了通过冷冻干燥去皮的兔乳头肌和股薄肌的快速骨骼肌纤维中Ca2+、Ba2+和Sr2+引起的力激活情况。Ba2+激活的长度-张力关系在最大值的数值和位置方面都与Sr2+和Ca2+激活的情况有显著差异。在（几乎）完全激活时，Ba2+在股薄肌中诱导的力是Ca2+诱导的最大力的50%。与Ca2+敏感性曲线的位置不同，乳头肌制剂的Sr2+敏感性曲线的位置与肌节长度无关。从激活后的持久松弛情况观察到，Sr2+与乳头肌制剂的结合非常稳定。用Ba2+激活后将乳头肌制剂浸入松弛液中会导致张力瞬变：观察到张力先升高后降低。张力瞬变的最大值高达稳定张力的两倍，这取决于Ba2+的浓度。稳定状态下的张力约为Ca2+诱导张力的50%。Ba2+敏感性曲线不是S形的，而是有一个最大值。当[Ba2+]大于10^(-5)至10^(-4) M（取决于肌节长度）时，张力下降。这些观察结果表明，有两个相互抵消的过程控制着乳头肌制剂中的Ba2+收缩，即激活和抑制。
