Karaki H, Weiss G B
J Pharmacol Exp Ther. 1980 Jun;213(3):450-5.
The relationships between contractile responses to stimulatory agents and changes in binding and distribution of La+++-resistant Ca++ at kinetically distinct high and low affinity sites were investigated. The magnitude of the norepinephrine (NE)-induced decrease in 45Ca retention (associated with release of high affinity Ca++) after exposure to La+++ and low temperature was similar when NE was present either for the entire 45Ca incubation period (40--120 min) or for as short an interval as the final minute of the incubation period. Under conditions favoring high affinity binding of Ca++, uptake of 45Ca was slow (T 1/2 approximately equal to 30 min) but the NE-induced decrease in 45Ca retention was rapid. Conversely, low affinity Ca++ sites load rapidly (T 1/2 less than or equal to 5 min) retain increased 45Ca in the presence of elevated (160 mM) K+ at all incubation intervals (5--120 min) and accumulate even more 45Ca in proportion to the increase in contraction obtained when NE is also present either for the entire incubation period or for only the final portion (1 min or longer). Similar effects on both high and low affinity binding of Ca++ are obtained with equipotent concentrations of NE and histamine. Simultaneous application of NE and histamine did not alter high and low affinity binding of Ca++ significantly more than did separate administration of either agent. These results indicate that NE and histamine effect similar high and low affinity Ca++ sites and that, even though equilibrium of Ca++ with high affinity sites is a much slower process than with low affinity sites, stimulatory agents can elicit rapid changes in the amount of Ca++ present at either site.
研究了对刺激剂的收缩反应与动力学上不同的高亲和力和低亲和力位点处抗镧钙（Ca++）结合及分布变化之间的关系。在暴露于镧（La+++）和低温后，当去甲肾上腺素（NE）在整个45Ca孵育期（40 - 120分钟）或仅在孵育期最后一分钟这么短的时间内存在时，NE诱导的45Ca保留量减少（与高亲和力Ca++释放相关）幅度相似。在有利于Ca++高亲和力结合的条件下，45Ca摄取缓慢（半衰期约为30分钟），但NE诱导的45Ca保留量减少迅速。相反，低亲和力Ca++位点加载迅速（半衰期小于或等于5分钟），在所有孵育间隔（5 - 120分钟）的高钾（160 mM）存在下保留增加的45Ca，并且与当NE在整个孵育期或仅在最后部分（1分钟或更长时间）存在时获得的收缩增加成比例地积累更多45Ca。用等效浓度的NE和组胺对Ca++的高亲和力和低亲和力结合都有类似影响。同时应用NE和组胺对Ca++高亲和力和低亲和力结合的改变并不比单独给予任何一种药物显著更多。这些结果表明，NE和组胺作用于类似的高亲和力和低亲和力Ca++位点，并且即使Ca++与高亲和力位点的平衡过程比与低亲和力位点的平衡过程慢得多，刺激剂仍可在任一位点引起Ca++含量的快速变化。
