Miyamota M D, Breckenridge B M
J Gen Physiol. 1974 May;63(5):609-24. doi: 10.1085/jgp.63.5.609.
The frequency of miniature endplate potentials (mepps) in rat diaphragms was markedly increased by epinephrine and norepinephrine in preparations exposed to 15 mM K(+). The effect was rapid in onset but gradually declined during continued exposure to the catecholamines. N(6), O(2')-dibutyryl adenosine 3',5'-monophosphate (dibutyryl-cAMP) also caused transient frequency increases resembling in time-course those observed with catecholamines. Contrary to previous reports, catecholamines and dibutyryl-cAMP had little effect on mepp frequency in preparations not treated with K(+). Sustained increases with theophylline and decreases with adenosine were found in both K(+)-treated and untreated preparations. Analysis of the data obtained with catecholamines showed the intensity of the response to be a function of nerve terminal polarization. The inability of catecholamines and dibutyryl-cAMP to affect mepp frequency of untreated preparations argues against an obligatory role for cAMP in the neurosecretory mechanism. The findings are consistent with an action of catecholamines and cAMP in the regulation of transmitter release at fatigued preparations.
在暴露于15 mM钾（K⁺）的大鼠膈肌标本中，肾上腺素和去甲肾上腺素显著增加了微小终板电位（mepps）的频率。这种效应起效迅速，但在持续暴露于儿茶酚胺期间逐渐下降。N⁶，O²'-二丁酰腺苷3'，5'-单磷酸（二丁酰-cAMP）也引起了类似于儿茶酚胺所观察到的时间进程的瞬时频率增加。与先前的报道相反，儿茶酚胺和二丁酰-cAMP对未用钾（K⁺）处理的标本中的mepp频率几乎没有影响。在钾（K⁺）处理和未处理的标本中均发现，茶碱可使频率持续增加，腺苷则使其降低。对儿茶酚胺获得的数据进行分析表明，反应强度是神经末梢极化的函数。儿茶酚胺和二丁酰-cAMP无法影响未处理标本的mepp频率，这与cAMP在神经分泌机制中起必要作用的观点相悖。这些发现与儿茶酚胺和cAMP在调节疲劳标本中递质释放的作用一致。
