Brozovich F V, Yamakawa M
Bockus Research Institute, Graduate Hospital, Philadelphia, Pennsylvania 19146.
Am J Physiol. 1993 Jan;264(1 Pt 1):C103-8. doi: 10.1152/ajpcell.1993.264.1.C103.
To determine cross-bridge properties during agonist-stimulated contractions, steady-state force and relative steady-state stiffness were recorded at rest (pCa 9) and during both full (pCa 4) and partial (pCa 7) Ca2+ activations of isolated single alpha-toxin permeabilized vascular smooth muscle cells. For pCa 4 and pCa 7, agonist (1 microM histamine) activation resulted in significant (P < 0.05) increases in both force and stiffness. The agonist-induced increase of steady-state force was significantly (P < 0.05) greater than that of stiffness; at pCa 4, there was a 48% increase for force vs. 17% for stiffness, and, at pCa 7, there was a 160% increase for force vs. 57% for stiffness. The increase in force and stiffness after agonist prestimulation implies that the number of attached cross bridges has increased. However, after agonist prestimulation, we found that the increase of force was greater (P < 0.05) than that of stiffness, resulting in a greater force at any given level of stiffness. Thus these data indicate that agonist activation, presumably via activation of a G protein, increases the relative force per attached cross bridge, possibly by modulating the kinetics of the actomyosin adenosinetriphosphatase to increase in the relative population of cross bridges in force-producing states [actinomyosin (AM) or AM.ADP].
为了确定激动剂刺激收缩过程中的横桥特性，在静息状态（pCa 9）以及分离的单个α-毒素通透的血管平滑肌细胞完全（pCa 4）和部分（pCa 7）Ca2+激活期间记录稳态力和相对稳态刚度。对于pCa 4和pCa 7，激动剂（1 microM组胺）激活导致力和刚度均显著（P < 0.05）增加。激动剂诱导的稳态力增加显著（P < 0.05）大于刚度增加；在pCa 4时，力增加48%，而刚度增加17%，在pCa 7时，力增加160%，而刚度增加57%。激动剂预刺激后力和刚度的增加意味着附着的横桥数量增加。然而，激动剂预刺激后，我们发现力的增加大于（P < 0.05）刚度的增加，导致在任何给定刚度水平下力更大。因此，这些数据表明，激动剂激活，可能是通过激活G蛋白，增加了每个附着横桥的相对力，可能是通过调节肌动球蛋白腺苷三磷酸酶的动力学，以增加处于产生力状态的横桥（肌动球蛋白（AM）或AM.ADP）的相对比例。
