Gunst S J, Pisoni J M
J Appl Physiol (1985). 1986 Aug;61(2):706-11. doi: 10.1152/jappl.1986.61.2.706.
Strips of canine tracheal smooth muscle were studied in vitro to determine the effects of changes in the extracellular calcium (Cao) concentration on tonic contractions induced by acetylcholine and 5-hydroxytryptamine. Strips were contracted with graded concentrations of the above agents in 2.4 mM Ca, after which CaCl2 was administered to achieve final concentrations of 5.0, 10.0, and 20.0 mM. Increases in Cao to 5 mM or above caused significant relaxation of muscles contracted with 5-hydroxytryptamine but did not significantly relax muscles contracted with acetylcholine. Increases in Cao also caused significant relaxation of muscles contracted with low concentrations of K+ (20 or 30 mM). However, in 60 or 120 mM K+, increases in Cao resulted predominantly in muscle contraction. Inhibition of the Na+-K+-ATPase by ouabain (10(-5) M) or K+ depletion reversed the effects of Cao from relaxation to contraction in tissues contracted with 5-hydroxytryptamine. Increases in Cao also caused contraction rather than relaxation in the presence of verapamil (10(-6) M). We conclude that calcium has both excitatory and inhibitory effects on the contractile responses of canine tracheal smooth muscle. The inhibitory effects of Ca2+ appear to be linked to the activity of the membrane Na+-K+-ATPase.
对犬气管平滑肌条进行体外研究，以确定细胞外钙（CaO）浓度变化对乙酰胆碱和5-羟色胺诱导的强直性收缩的影响。在2.4 mM钙的条件下，用上述药物的分级浓度使肌条收缩，之后给予氯化钙以达到5.0、10.0和20.0 mM的终浓度。将CaO增加到5 mM或更高会导致用5-羟色胺收缩的肌肉显著松弛，但不会使用乙酰胆碱收缩的肌肉显著松弛。CaO增加也会导致用低浓度钾（20或30 mM）收缩的肌肉显著松弛。然而，在60或120 mM钾的情况下，CaO增加主要导致肌肉收缩。哇巴因（10⁻⁵ M）抑制钠钾ATP酶或钾耗竭会使在用5-羟色胺收缩的组织中，CaO的作用从松弛转变为收缩。在维拉帕米（10⁻⁶ M）存在的情况下，CaO增加也会导致收缩而非松弛。我们得出结论，钙对犬气管平滑肌的收缩反应既有兴奋作用又有抑制作用。Ca²⁺的抑制作用似乎与膜钠钾ATP酶的活性有关。
