Cell Biology Poster Session
Njanoor, Narayanan (Department of Physiology, The University of Western Ontario, Canada)
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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|Mao, Jiang; Njanoor, Narayanan; (1998). Thyroid Hormone-induced Alterations in Sarcoplasmic Reticulum (SR) Protein Phosphorylation and Ca2+ Pump Activity. Presented at INABIS '98 - 5th Internet World Congress on Biomedical Sciences at McMaster University, Canada, Dec 7-16th. Available at URL http://www.mcmaster.ca/inabis98/cellbio/mao0393/index.html|
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