Usune S, Katsuragi T, Sakamoto Y, Furukawa T
Can J Physiol Pharmacol. 1986 Jun;64(6):720-3. doi: 10.1139/y86-121.
The contribution of Na+ and membrane depolarization to biphasic contractions induced by adrenaline were investigated in the smooth muscle of guinea pig vas deferens. Adrenaline (5 X 10(-6) M) produced an initial small contraction (first contraction) followed by a large tonic contraction (second contraction) with subsequent rhythmic activity. The entire response to adrenaline was largely inhibited by phentolamine (5 X 10(-6) M). By adding an appropriate concentration of Mn2+ (2 X 10(-4) M) or nifedipine (3 X 10(-7) M), a Ca2+ blocker, the second contraction was strongly reduced, accompanied by abolishment of the rhythmic contraction, whereas the first contraction was virtually unaffected. However, the first contraction was markedly suppressed by a higher concentration of Mn2+. All contractions produced by adrenaline were greatly reduced in Ca2+-free solution containing 0.5 mM EGTA. By lowering external Na+ concentration, the first contraction was markedly increased without greatly affecting the second contraction. By exposure to Na+-free isotonic high K+ solution, which elicited a greater depolarization of the membrane, the first contraction produced by adrenaline was also greatly potentiated, while the second and rhythmic contractions were eliminated. These results suggest that the adrenaline-evoked first contraction may be due to an influx of membrane bound Ca2+ which is independent of membrane depolarization, while the second (rhythmic) contraction is due to an influx of extracellular Ca2+ which is dependent upon depolarization.
在豚鼠输精管平滑肌中研究了钠离子（Na⁺）和膜去极化对肾上腺素诱导的双相收缩的作用。肾上腺素（5×10⁻⁶ M）产生一个初始的小收缩（第一次收缩），随后是一个大的强直收缩（第二次收缩），并伴有随后的节律性活动。对肾上腺素的整个反应在很大程度上被酚妥拉明（5×10⁻⁶ M）抑制。通过添加适当浓度的锰离子（Mn²⁺，2×10⁻⁴ M）或钙离子阻滞剂硝苯地平（3×10⁻⁷ M），第二次收缩被强烈减弱，同时节律性收缩消失，而第一次收缩几乎不受影响。然而，较高浓度的锰离子会显著抑制第一次收缩。在含有0.5 mM乙二醇双四乙酸（EGTA）的无钙溶液中，肾上腺素产生的所有收缩都大大减弱。通过降低细胞外钠离子浓度，第一次收缩显著增强，而对第二次收缩影响不大。通过暴露于能引起更大膜去极化的无钠等渗高钾溶液中，肾上腺素产生的第一次收缩也大大增强，而第二次和节律性收缩则消失。这些结果表明，肾上腺素诱发的第一次收缩可能是由于与膜去极化无关的膜结合钙离子内流所致，而第二次（节律性）收缩是由于依赖去极化的细胞外钙离子内流所致。
