Leijten P A, van Breemen C
Br J Pharmacol. 1986 Dec;89(4):739-47. doi: 10.1111/j.1476-5381.1986.tb11178.x.
Cellular Ca2+ recycling in a branch of the rabbit mesenteric artery was investigated by measuring the time- and concentration-dependent effects of noradrenaline (NA) on contraction and 45Ca efflux in Ca2+-free solution. When NA was present continuously (15 min), both force development and 45Ca efflux stimulation consisted of a fast and a slow (often oscillatory) component. These components were sensitive to caffeine and are probably both related to Ca2+ release from the intracellular Ca2+ store, presumably sarcoplasmic reticulum (s.r.). When NA was applied for shorter time periods, both tension and stimulated 45Ca efflux decreased similarly. Repetitive short (30 s) NA applications resulted in repeated contractions and stimulations of 45Ca efflux. The NA-stimulated 45Ca efflux was not inhibited when external Ca2+ was present or in Na+-free medium. Loading the cell with Ca2+ (with physiological salt solution for 3 h or with a high K+ depolarizing solution) increases the number of subsequent NA-induced repeated contractions in Ca2+-free solution. The Ca2+ content of the sarcoplasmic reticulum (s.r.) in the smooth muscle cells of this small artery was estimated to be at least 50 mumol kg-1 wet weight, corresponding to an s.r. Ca2+ concentration of about 3.1 mM. These results indicate that the NA-induced increase in cytosolic free Ca2+ (as measured by force development) is accompanied by an increase in Ca2+ extrusion (as measured by stimulation of 45Ca efflux). This suggests that at least part of the activator Ca2+ cycles through the extracellular space during hormone-induced activation of vascular smooth muscle.
通过测量去甲肾上腺素（NA）在无钙溶液中对收缩和45Ca外流的时间和浓度依赖性影响，研究了兔肠系膜动脉一个分支中的细胞钙回收情况。当持续存在NA（15分钟）时，力的产生和45Ca外流刺激均由快速和缓慢（通常为振荡性）成分组成。这些成分对咖啡因敏感，可能都与细胞内钙库（推测为肌浆网，s.r.）释放钙有关。当短时间应用NA时，张力和刺激的45Ca外流均以相似的方式下降。重复短时间（30秒）应用NA会导致45Ca外流的重复收缩和刺激。当存在细胞外钙或在无钠培养基中时，NA刺激的45Ca外流不受抑制。用钙（用生理盐溶液处理3小时或用高钾去极化溶液处理）加载细胞会增加随后在无钙溶液中NA诱导的重复收缩次数。估计这条小动脉平滑肌细胞中肌浆网（s.r.）的钙含量至少为50 μmol kg-1湿重，对应于约3.1 mM的肌浆网钙浓度。这些结果表明，NA诱导的胞质游离钙增加（通过力的产生来测量）伴随着钙外流增加（通过刺激45Ca外流来测量）。这表明在激素诱导的血管平滑肌激活过程中，至少部分激活钙通过细胞外空间循环。
