Prakash Y S, van der Heijden H F, Gallant E M, Sieck G C
Departments of Anesthesiology and of Physiology and Biophysics, Mayo Clinic and Foundation, Rochester 55905, Minnesota, USA.
Am J Physiol. 1999 May;276(5):C1038-45. doi: 10.1152/ajpcell.1999.276.5.C1038.
The present study used real-time confocal microscopy to examine the effects of the beta2-adrenoceptor agonist salbutamol on regulation of intracellular Ca2+ concentration ([Ca2+]i) in myotubes derived from neonatal mouse limb muscles. Immunocytochemical staining for ryanodine receptors and skeletal muscle myosin confirmed the presence of sarcomeres. The myotubes displayed both spontaneous and ACh-induced rapid (<2-ms rise time) [Ca2+]i transients. The [Ca2+]i transients were frequency modulated by both low and high concentrations of salbutamol. Exposure to alpha-bungarotoxin and tetrodotoxin inhibited ACh-induced [Ca2+]i transients and the response to low concentrations of salbutamol but not the response to higher concentrations. Preexposure to caffeine inhibited the subsequent [Ca2+]i response to lower concentrations of salbutamol and significantly blunted the response to higher concentrations. Preexposure to salbutamol diminished the [Ca2+]i response to caffeine. Inhibition of dihydropyridine-sensitive Ca2+ channels with nifedipine or PN-200-110 did not prevent [Ca2+]i elevations induced by higher concentrations of salbutamol. The effects of salbutamol were mimicked by the membrane-permeant analog dibutyryl adenosine 3', 5'-cyclic monophosphate. These data indicate that salbutamol effects in skeletal muscle predominantly involve enhanced sarcoplasmic reticulum Ca2+ release.
本研究采用实时共聚焦显微镜检查β2-肾上腺素能受体激动剂沙丁胺醇对新生小鼠肢体肌肉来源的肌管细胞内钙离子浓度（[Ca2+]i）调节的影响。对兰尼碱受体和骨骼肌肌球蛋白进行免疫细胞化学染色，证实了肌节的存在。这些肌管显示出自发性和乙酰胆碱诱导的快速（上升时间<2毫秒）[Ca2+]i瞬变。[Ca2+]i瞬变受到低浓度和高浓度沙丁胺醇的频率调制。暴露于α-银环蛇毒素和河豚毒素可抑制乙酰胆碱诱导的[Ca2+]i瞬变以及对低浓度沙丁胺醇的反应，但不影响对高浓度沙丁胺醇的反应。预先暴露于咖啡因可抑制随后对较低浓度沙丁胺醇的[Ca2+]i反应，并显著减弱对较高浓度沙丁胺醇的反应。预先暴露于沙丁胺醇可减弱对咖啡因的[Ca2+]i反应。用硝苯地平或PN-200-110抑制二氢吡啶敏感的Ca2+通道并不能阻止高浓度沙丁胺醇诱导的[Ca2+]i升高。沙丁胺醇的作用可被膜通透性类似物二丁酰腺苷3'，5'-环磷酸模仿。这些数据表明，沙丁胺醇在骨骼肌中的作用主要涉及增强肌浆网Ca2+释放。
