Kaasik A, Minajeva A, Paju K, Eimre M, Seppet E K
Department of Pathophysiology, University of Tartu, Estonia.
Mol Cell Biochem. 1997 Nov;176(1-2):119-26.
The present study was undertaken to compare the effects of hypothyroidism and hyperthyroidism on sarcoplasmic reticulum (SR) Ca(2+)-pump activity, together with assessment of the functional role of SR in providing activator Ca2+ under these altered thyroid states. In response to a shift from hypothyroid to hyperthyroid state, a 10 fold and 2 fold increase in SR Ca(2+)-pump activity in atria and ventricles, respectively, were observed. This was associated with the 8-9 fold increases in atrial contractility (+dT/dt) and relaxation (-dT/dt), but only with a 3-4 fold increase in their ventricular counterparts. Also, the recirculation fraction of activator Ca2+ (RFA) increased to a far greater extent in atria (4 fold) than in papillary muscles, and the relative increment in inhibition of developed tension by ryanodine became 3 times larger in atria than in papillary muscles. A positive force-frequency relationship (FFR) was observed in hypothyroid atria, whereas the hyperthyroid atria, hypothyroid and hyperthyroid papillary muscles showed a negative FFR. These results suggest the greater role of transsarcolemmal (SL) Ca2+ and smaller role of SR Ca2+ in activating contraction in hypothyroid atria compared to other preparations. Thyroid hormones decrease the contribution of SL and increase that of SR in providing activator Ca2+ to the greater extent in atria than in ventricles. This effect of thyroid hormones is based on larger stimulation of SR Ca(2+)-pump in atria compared to ventricles.
本研究旨在比较甲状腺功能减退和甲状腺功能亢进对肌浆网（SR）Ca²⁺泵活性的影响，并评估在这些甲状腺状态改变的情况下SR在提供激活剂Ca²⁺方面的功能作用。从甲状腺功能减退状态转变为甲状腺功能亢进状态时，观察到心房和心室中SR Ca²⁺泵活性分别增加了10倍和2倍。这与心房收缩性（+dT/dt）和舒张（-dT/dt）增加8 - 9倍相关，但心室的相应增加仅为3 - 4倍。此外，激活剂Ca²⁺的再循环分数（RFA）在心房中的增加程度（4倍）远大于乳头肌，并且ryanodine对发达张力的抑制作用的相对增量在心房中比在乳头肌中大三倍。在甲状腺功能减退的心房中观察到正力 - 频率关系（FFR），而甲状腺功能亢进的心房、甲状腺功能减退和甲状腺功能亢进乳头肌表现出负FFR。这些结果表明，与其他制剂相比，在甲状腺功能减退的心房中，跨肌膜（SL）Ca²⁺在激活收缩中的作用更大，而SR Ca²⁺的作用较小。甲状腺激素在心房中比在心室中更大程度地降低了SL的贡献并增加了SR在提供激活剂Ca²⁺方面的贡献。甲状腺激素的这种作用是基于与心室相比，对心房中SR Ca²⁺泵的更大刺激。
