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PubMed · 9406153

Thyroid hormones differentially affect sarcoplasmic reticulum function in rat atria and ventricles.

A Kaasik·A Minajeva·K Paju·M Eimre·E K Seppet
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Abstract

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.

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Actin CytoskeletonAnimalsCalciumCalcium-Transporting ATPasesCardiotonic AgentsFemaleHeartHeart AtriaHeart VentriclesHyperthyroidismHypothyroidismMaleMyocardial ContractionPapillary MusclesRatsRats, WistarRyanodineSarcoplasmic ReticulumStimulation, ChemicalThyroid HormonesJournal ArticleResearch Support, Non-U.S. Gov't

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A Kaasik, A Minajeva, K Paju, M Eimre, E K Seppet. 1997. Thyroid hormones differentially affect sarcoplasmic reticulum function in rat atria and ventricles.. https://pubmed.ncbi.nlm.nih.gov/9406153/

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