Ito Y, Itoh T
Br J Pharmacol. 1984 Nov;83(3):667-76. doi: 10.1111/j.1476-5381.1984.tb16220.x.
Effects of direct or indirect (nerve-mediated) muscle stimulation, acetylcholine (ACh), caffeine and procaine on the membrane and mechanical properties of smooth muscle cells of the cat trachea were investigated by means of double sucrose-gap and isometric tension recording methods. Outward current pulses (2 s in duration) applied to the muscle tissue in the presence of tetrodotoxin (10(-7)M), atropine (10(-6)M) and propranolol (10(-6)M) evoked no action potential (spike); however, when the depolarization exceeded 9 mV, a contraction was evoked. The spike and contraction evoked by outward current pulses in the presence of tetraethylammonium (TEA, 10 mM) were suppressed by treatment of the tissue with either Ca2+-free EGTA (2 mM) containing solution or Mn2+ (5 mM). In the presence of procaine (10 mM), outward current pulses evoked an action potential but no contraction. Field stimulation of short duration (50 microseconds) applied to the whole tissue produced an excitation of the intrinsic nerves and evoked excitatory junction potentials (e.j.ps), and when the amplitude of e.j.ps exceeded 4 mV, a twitch contraction occurred. E.j.p. was more effective in producing a contraction than was the membrane depolarization evoked by outward current pulses. Amplitudes of contractions evoked by exogenous ACh (10(-5)M) were much larger than those evoked by 128 mM-[K]0 or caffeine (10 mM), in normal Krebs solution. When the amplitudes of the contractions produced by 128 mM [K]0 were defined as a relative amplitude of 1.0, the mean amplitudes of contraction produced by ACh (10(-5)M) or caffeine were 2.5 +/- 0.20 or 1.2 +/- 0.26, respectively. In Ca2+-free EGTA (2 mM)-containing solution, the contraction induced by 128 mM-[K]0 was rapidly abolished, whereas the contractions evoked by caffeine (10 mM) or the initial phasic contraction produced by ACh (10(-5)M) were largely unaffected. When the amount of Ca2+ stored in the muscle cell was estimated from the amplitude of caffeine-induced contraction evoked in Ca2+-free solution, procaine (10 mM) applied simultaneously with Ca2+, after depletion of Ca2+ from the cells by means of caffeine, increased the amount of Ca2+ stored to 1.31 +/- 0.14 (n = 6) times the control value. However, ACh (10(-7)M) or excess concentrations of [K]0 applied with Ca2+ did not increase the amount of Ca2+ stored in the caffeine-sensitive intracellular compartment. 8 These results indicate that the amount of Ca2 + stored in the smooth muscle cells of the cat trachea may be larger than other visceral smooth muscle and plays an important role in the initiation of contraction, in response to endogenous or exogenous ACh.
采用双蔗糖间隙和等长张力记录方法，研究了直接或间接（神经介导）的肌肉刺激、乙酰胆碱（ACh）、咖啡因和普鲁卡因对猫气管平滑肌细胞膜及力学特性的影响。在存在河豚毒素（10⁻⁷M）、阿托品（10⁻⁶M）和普萘洛尔（10⁻⁶M）的情况下，施加于肌肉组织的外向电流脉冲（持续时间2秒）未诱发动作电位（尖峰）；然而，当去极化超过9mV时，会诱发收缩。在存在四乙铵（TEA，10mM）的情况下，外向电流脉冲诱发的尖峰和收缩可通过用含无钙EGTA（2mM）的溶液或Mn²⁺（5mM）处理组织来抑制。在存在普鲁卡因（10mM）的情况下，外向电流脉冲诱发动作电位但不诱发收缩。对整个组织施加短持续时间（50微秒）的场刺激可激发内在神经并诱发兴奋性接头电位（e.j.ps），当e.j.ps的幅度超过4mV时，会发生抽搐收缩。E.j.p.在产生收缩方面比外向电流脉冲诱发的膜去极化更有效。在正常Krebs溶液中，外源性ACh（10⁻⁵M）诱发的收缩幅度远大于128mM-[K]₀或咖啡因（10mM）诱发的收缩幅度。当将128mM [K]₀产生的收缩幅度定义为相对幅度1.0时，ACh（10⁻⁵M）或咖啡因产生的收缩平均幅度分别为2.5±0.20或1.2±0.26。在含无钙EGTA（2mM）的溶液中，128mM-[K]₀诱发的收缩迅速消失，而咖啡因（10mM）诱发的收缩或ACh（10⁻⁵M）产生的初始相收缩基本不受影响。当根据无钙溶液中咖啡因诱发的收缩幅度估计肌肉细胞中储存的Ca²⁺量时，在通过咖啡因使细胞内Ca²⁺耗尽后，与Ca²⁺同时施加的普鲁卡因（10mM）可将储存的Ca²⁺量增加至对照值的1.31±0.14（n = 6）倍。然而，与Ca²⁺同时施加的ACh（10⁻⁷M）或过量浓度的[K]₀并未增加咖啡因敏感细胞内区室中储存的Ca²⁺量。这些结果表明，猫气管平滑肌细胞中储存的Ca²⁺量可能比其他内脏平滑肌细胞中的更大，并且在响应内源性或外源性ACh时在收缩的起始中起重要作用。
