Hong K W, Biancani P, Weiss R M
Am J Physiol. 1985 Jan;248(1 Pt 1):C165-9. doi: 10.1152/ajpcell.1985.248.1.C165.
The in vitro guinea pig ureter responds to 5-s trains of electrical stimuli with two contractions: the first, an "on" response, occurs within 0.1-0.3 s after the onset of the stimulus train; the second, an "off" response, occurs 0.2-1.0 s after the termination of the stimulus train. Force decreases between the two responses during a time when the stimulus is still being delivered. Longer duration and/or higher frequencies of stimuli within the train are required to elicit the off response than the on response. Neither the on nor the off response appears to be neurally mediated, since both responses are unchanged by tetrodotoxin, phentolamine, atropine, and pyrilamine. Decreasing temperature from 37 to 22 degrees C decreases the amplitude of the on response and increases the amplitude of the off response. Calcium-free solution, 2 mM ethylenediaminetetraacetic acid (EDTA), 1 mM Mn2+, and 1 microM verapamil abolish the on response at a time at which the off response continues to persist. Conversely, 0.5 mM caffeine and 0.1 mM theophylline abolish the off response, whereas they only slightly reduce the on response. These data suggest that the on response depends on extracellular free calcium, whereas the off response is more dependent on bound or stored calcium.
豚鼠离体输尿管对5秒的电刺激串有两种收缩反应：第一种是“开”反应，在刺激串开始后0.1 - 0.3秒内出现；第二种是“关”反应，在刺激串终止后0.2 - 1.0秒出现。在刺激仍在施加期间，两次反应之间的力量会下降。与“开”反应相比，引发“关”反应需要刺激串中更长的持续时间和/或更高的频率。“开”反应和“关”反应似乎都不是由神经介导的，因为这两种反应在使用河豚毒素、酚妥拉明、阿托品和吡苄明后都没有变化。将温度从37℃降至22℃会降低“开”反应的幅度，并增加“关”反应的幅度。无钙溶液、2 mM乙二胺四乙酸（EDTA）、1 mM Mn2 +和1 μM维拉帕米在“关”反应仍持续存在时消除了“开”反应。相反，0.5 mM咖啡因和0.1 mM茶碱消除了“关”反应，而它们仅略微降低了“开”反应。这些数据表明，“开”反应依赖于细胞外游离钙，而“关”反应更依赖于结合钙或储存钙。
