Abstract

Introduction

Materials & Methods

Results

Discussion & Conclusion

References

Discussion
Board

Previous studies have shown altered SR Ca2+-ATPase and Phospholamban (PLN) gene expression in thyrotoxic cardiac hypertrophy. The present study determined the impact of L-thyroxine-induced hyperthyroidism on CaM kinase mediated SR protein phosphorylation and SR Ca2+ pump activity in cardiac and slow=twitch skeletal muscle (soleus) of rabbit. Western blotting analysis revealed a significant increase (30-50%) in the SERCA2 Ca2+ pump isoform in cardiac muscle, and SERCA1 Ca2+ pump isoform in soleus muscle, in the hyperthyroid compared to euthyroid. The relative amount of PLN was ~30% lower in both hyperthyroid tissues. Cardiac and soleus SR from hyperthyroid rabbits displayed significantly greater rates (~40%) of Ca2+ uptake and Ca2+-ATPase activities. However, endogenous CaM kinase mediated phosphorylation of Ca2+-ATPase and PLN was significantly lower (30-50%) in cardiac and soleus SR from hyperthyroid compared to euthyroid. These findings suggest that (a) overexpression of different SR Ca2+-ATPase isoforms contributes to the enhanced SR Ca2+ sequestration in hyperthyroid heart and slow-twitch soleus muscle; and (b) the expression of Ca2+-ATPase and PLN are not co-ordinately regulated in both tissues. (Supported by MRC of Canada).

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Poster Number PAmao 0393
Keywords: Thyroid hormone, SR, Ca2+ pump, PLN