BETA-ADRENERGIC MODULATION OF CARDIAC FUNCTION

β-肾上腺素能激动剂增加心肌收缩幅度和 加强放松。我们的研究考察了自主性神经调节 钙-肌钙蛋白的相互作用以确定它是否可以解释 增强的抽搐放松。在单个心肌细胞中，我们发现对于 细胞内钙离子收缩的给定幅度较小。 异丙肾上腺素(Iso)水平明显高于对照组。在肌细胞悬液中 去甲肾上腺素(NE，10um)使肌钙蛋白I磷酸化增加四倍 在相似的条件下，个体的抽动松弛时间缩短 肌细胞数增加20%。普奈洛尔(1.0微米)后肌钙蛋白缓慢 去磷酸化(半场16.9±1.7分钟)，但完全松弛时间 在5分钟内恢复控制。因此，肌钙蛋白-I的-范围 去甲肾上腺素的磷酸化并不与其影响成正比 放松时间。 在离体雪貂心肌中注射水飞蓟素引起的钙张力 根据峰的Aequorin发光与峰之间的关系 在存在的大范围沐浴钙上测量的张力 不含乙酰胆碱(ACh，1um)和/或Iso(1um)。ACH 将峰值张力的关系左移到光的(峰值)平衡， 提示肌钙敏感性增加，但没有 改变抽动松弛(tl/2r)。ISO移动了峰的关系 向右张力达峰值，tl/2R降低。ACH添加到 国际标准化组织取消了峰值张力-等效光关系中的等效应 但不能逆转Iso降低tl/2R的作用。因此， 心肌细胞表观肌丝钙相互作用的扰动 完整的肌肉并不一定与抽搐放松时间有关。

Beta-adrenergic agonists increase the myocardial contraction amplitude and enhance relaxation. 0ur studies examine the autonomic modulation of the calcium-myofila-ment interaction to determine whether it could account for enhanced twitch relaxation. In single cardiac myocytes we found that for a given amplitude of-cytosolic calcium twitch amplitude was less in isoproterenol (Iso) than in control. In myocytes suspensions norepinephrine (NE, 10 uM) increased troponin-I phosphorylation fourfold and under similar conditions decreased twitch relaxation time in individual myocytes by 20%. After propranolol (1.0 uM) troponin slowly dephosphorylated (half time 16.9+1.7 min) but relaxation time fully returned to control within 5 min. Thus, the -extent of troponin-I phosphorylation by NE is not directly proportional to its effect on relaxation time. In isolated, aequorin-injected ferret cardiac muscle the calcium tension relation was determined from the peak aequorin luminescence and peak tension measured across a broad range of bathing calcium in the presence and absence of acetyl-choline (ACh, I uM) or Iso (1 uM) or both drugs. Ach shifted the relationship of peak tension to (peak) aequorin light leftward, suggesting an increase in myofila-ment calcium sensitivity, but did not alter twitch relaxation (tl/2R). Iso shifted the relationship of peak tension to peak aequorin light rightward and decreased tl/2R. Ach added to Iso abolished the Iso effect on peak tension-aequorin light relationship but did not reverse the effect of Iso to decrease tl/2R. Thus per-turbations of the apparent myofilament calcium interaction in the intact muscle do not necessarily relate to twitch relaxation time.