Simultaneous assay of Calcium antagonistic and other antispsmodic activities of smooth muscle relaxants by "Ca reversal" phenomenon.

众所周知，钙离子是一种生理反应的触发者，在大鼠子宫平滑肌中，它也可能在较低浓度的情况下作为一种反应的抑制因子。加入静息水平的钙离子(-lt；10^(-8)&gt；-lt；10^(-7)&gt；M)，可逆转无钙溶液中催产素引起的子宫平滑肌收缩。这种钙离子的松弛称为“钙逆转”。这一发现表明，低浓度的钙离子具有抑制作用。钙拮抗剂的存在使细胞内钙离子发生逆转。因此，我们测试了这一现象用于测定钙拮抗活性的可行性。结果发现，该系统非常简单，判断要么全有要么全无，而且由于可以同时确定其他解痉性动作，因此非常有用。各种药物逆转钙的&lt；ED_(50)和Gt；值反映了它们的钙拮抗活性。~lt；10^(-4)&gt；M Ca离子和3x&lt；10^(-4)&gt；M Ca离子的~lt；ED_(50)&gt；值之比代表药物对钙通道的选择性。此外，在高&lt；K^+&gt；溶液中的比率清楚地表明了钙拮抗剂对电压操作的钙通道的选择性。因此，该系统对钙拮抗活性的测定是非常有用的，而钙拮抗活性对药物治疗非常重要。

Ca ion, which is well known as a trigger of physiological responses may also act as an inhibitor of responses in lower concentrations than those act as triggers in rat uterine smooth muscle. Addition of resting level of Ca ion ( <10^(-8)> - <10^(-7)> M) reversed the contraction by oxytocin of uterine smooth muscle in Ca free solution after preincubation with 3mM EGTA for 1hr. This relaxation by Ca ion was named "Calcium reversal". This finding suggests that Ca ion at low concentrations has an inhibitory action. Ca reversal is manifested in the presence of Ca antagonists. So we tested availability of this phenomenon for the assay of Ca antagonistic activity. It was found that the system is very simple as the judgement is all or none and it is very useful because other antispasmodic actions can be determined simultaneously. <ED_(50)> values for Ca reversal of various drugs show their Ca antagonistic activity. The ratios of <ED_(50)> values for <10^(-4)> M Ca ion and for 3x <10^(-4)> M Ca ions represent selectivity of a drug for Ca channels. Further, the ratio in high <K^+> solution clearly shows the selectivity of a Ca antagonist for voltage-operated Ca channels. Thus this system is very useful for the assay of Ca antagonistic activities, which are very important for drug therapy.