Parker I, Ito Y, Kuriyama H, Miledi R
Proc R Soc Lond B Biol Sci. 1987 Mar 23;230(1259):207-14. doi: 10.1098/rspb.1987.0016.
Intracellular free-calcium levels were measured in strips of longitudinal smooth muscle from guinea-pig ileum; fura-2 was used as a calcium monitor. At rest the calcium concentration was about 180 nM, and this rose to 300-400 nM following electrical stimulation and during spontaneous calcium transients (all measurements at 23-25 degrees C). Isoprenaline suppressed the spontaneous calcium transients, and reduced the resting calcium level to about 130 nM. This fall in resting calcium concentration was seen even in muscle strips which did not have spontaneous activity. Elevation of intracellular cyclic AMP levels, produced by forskolin or dibutyryl cyclic AMP, mimicked the actions of isoprenaline. We conclude that the relaxant effects of beta-adrenergic agonists of visceral smooth muscle may be explained partly by a fall in intracellular resting free-calcium level, mediated via an increase in cyclic AMP.
在豚鼠回肠纵行平滑肌条中测量细胞内游离钙水平；使用fura-2作为钙监测器。静息时钙浓度约为180 nM，电刺激后以及在自发钙瞬变期间（所有测量均在23 - 25摄氏度下进行），该浓度升至300 - 400 nM。异丙肾上腺素抑制自发钙瞬变，并将静息钙水平降至约130 nM。即使在没有自发活动的肌肉条中也能观察到静息钙浓度的这种下降。由福斯可林或二丁酰环磷酸腺苷引起的细胞内环磷酸腺苷水平升高，模拟了异丙肾上腺素的作用。我们得出结论，内脏平滑肌β - 肾上腺素能激动剂的舒张作用可能部分归因于细胞内静息游离钙水平的下降，这是通过环磷酸腺苷的增加介导的。
