ABSTRACT
AIM:To observe the effect of thyroxine on the expression of T-type calcium channels Cav3. 1, Cav3. 2 and Cav3. 3 in rat myocardium, and to explore the possible biological mechanism between the changes of the ex-pression of T-type calcium channels and the arrhythmia in hyperthyroid heart disease. METHODS:Healthy SD rats (n=20) were randomly divided into normal control group (n=10) and hyperthyroid heart disease group (n=10). The animal model was established by intraperitoneal injection of levothyroxine for 35 d. The contents of T3 and T4 in serum, the heart-to-body weight ratio, the diameter of cardiac myocytes and electrocardiograph were measured to evaluate hyperthyroid heart disease. Moreover, the mRNA and protein expression levels of T-type calcium channels in the myocardium were measured by RT-PCR, immunohistochemistry and Western blot. RESULTS:After intraperitoneal injection of levothyroxine for 35 d, compared with the normal control group, the serum contents of T3 and T4, the heart-to-body weight ratio and the diameter of cardiac myocytes were significantly increased in hyperthyroid heart disease group (P<0.05), and arrhythmia occurred in hyperthyroid heart disease group. By immunohistochemistry and Western blot, the protein expression of Cav3. 1 in-creased significantly (P<0.05), while the protein expression of Cav3.2 decreased significantly (P<0.01). However, no change of the Cav3. 3 protein was observed. The results of RT-PCR were the same as immunohistochemistry and Western blot. CONCLUSION:Thyroxine promotes the expression of Cav3. 1 in the myocardium but inhibits the expression of Cav3. 2 at mRNA and protein levels, which might be involved in arrhythmia in hyperthyroid heart disease.