Thyroid hormone increased L-type calcium channel mRNA expression and L-type calcium current of myocytes in rabbits.

OBJECTIVES:To investigate the effects of thyroid hormone on L-type calcium channel mRNA and L-type calcium current of atrium and ventricle. METHODS:Sixteen New Zealand white rabbits were randomized into Thyroxine group (n=8) and Control group (n=8). In Throxine group, rabbits were injected intraperitoneally with L-thyroxine solution for 2 weeks (1 mg/kg·d(-1)) to induce hyperthyroidism. In Control group, rabbits were injected with the same volume of saline as for Thyroxine group. On day 15, 4 rabbits in each group were killed randomly to exam the L-type calcium current of atrium and ventricle using whole cell patch clamp; the other 4 rabbits were killed to detect the expression of L-type calcium channel mRNA using RT-PCR. RESULTS:The mean peak of L-type calcium current densities (pA/pF) at -10 mV was higher in Thyroxine group than in Control group (-8.59±0.68 vs. -6.54±0.49 in atrium, n=8, p<0.001; -9.24±0.67 vs. -7.06±0.21 in ventricle, n=8, p<0.001). L-calcium channel mRNA expression of both atrial myocytes and ventricular cells in Thyroxine group was significantly higher than those in Control group (p<0.05). CONCLUSIONS:Extrinsic thyroid hormone increased expression of L-type calcium channel mRNA and ICa,L current densities in both atrium and ventricle. These changes infer that supplement of thyroid hormone may ameliorate myocardial contraction in some special conditions such as sepsis.

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