Wood E H, Allen D G, Jewell B R
Recent Adv Stud Cardiac Struct Metab. 1975;8:201-17.
If the frequency of stimulation of isolated kitten right ventricular papillary muscles is progressively reduced, the size of contractions decreases until a frequency is reached (rested state rate) where further reduction produces no change (rested state contraction, Koch-Weser and Blinks, 1963). At 30 degrees C and 2.25 mM Ca++, the rested state rate was about one per 2-5 min, the peak tension of 0.2-0.6 g/mm2 was about 5-15% of the tension of 20/min beats, and times to peak tension and 80% repolarization about doubled. Sudden calcium increases in the perfusion fluid, [Ca++]p, from 2.25 to 6.75 mM were produced at random during intervals between rested state contractions, and time and amplitude of peak isometric tension, max +/- dT/dt of subsequent beats were studied. The greatest positive inotropic response of the initial beats following increments in [Ca++]p resulted when [Ca++]p was increased immediately after a rested state contraction: as the postsystolic interval before the [Ca++]p increment was increased, the positive inotropic effects decreased approximately exponentially, attaining a plateau level in about 30 sec. This plateau was then maintained until the period prior to the initial test beat in high calcium was less than the approximately 2-min diffusion equilibrium time between [Ca++]p and the interior of the fiber.
如果逐渐降低对离体小猫右心室乳头肌的刺激频率，收缩幅度会减小，直到达到某一频率（静息状态频率），在此频率之下进一步降低频率不会产生变化（静息状态收缩，Koch-Weser和Blinks，1963年）。在30摄氏度和2.25毫摩尔/升钙离子浓度下，静息状态频率约为每2 - 5分钟一次，0.2 - 0.6克/平方毫米的峰值张力约为每分钟20次搏动张力的5 - 15%，达到峰值张力和80%复极化的时间约增加一倍。在静息状态收缩的间隔期间随机使灌注液中的钙离子浓度[Ca++]p从2.25毫摩尔/升突然增加到6.75毫摩尔/升，并研究随后搏动的等长张力峰值的时间和幅度、最大±dT/dt。[Ca++]p增加后最初搏动的最大正性肌力反应出现在静息状态收缩后立即增加[Ca++]p时：随着[Ca++]p增加前的收缩后期间隔增加，正性肌力作用大致呈指数下降，约30秒后达到平台期。然后维持该平台期，直到高钙状态下初始测试搏动前的时期小于[Ca++]p与纤维内部之间约2分钟的扩散平衡时间。
