R. Shenoy et al., Differential regulation of SR calcium transporters by thyroid hormone in rat atria and ventricles, AM J P-HEAR, 281(4), 2001, pp. H1690-H1696
Citations number
33
Categorie Soggetti
Cardiovascular & Hematology Research
Journal title
AMERICAN JOURNAL OF PHYSIOLOGY-HEART AND CIRCULATORY PHYSIOLOGY
Thyroid hormone exerts positive inotropic effects on the heart mediated in
part by its regulation of calcium transporter proteins, including sarco(end
o)plasmic reticulum Ca2+-ATPase (SERCA2), phospholamban (PLB), and Na+/Ca2 exchanger (NCX). To further understand the potential cardiac chamber-speci
fic effects of thyroid hormone action, we compared the triiodo-L-thyronine
(T-3) responsiveness of calcium transporter proteins in atrial versus ventr
icular tissues. Rats were rendered hypothyroid by ingestion of propylthiour
acil, and a subgroup of animals was treated with T-3 for 7 days (7 mug/day
by constant infusion). Atrial and left ventricular (LV) tissue homogenates
were analyzed for expression of SERCA2, PLB, and NCX proteins by Western bl
ot analysis. SERCA2 protein significantly decreased by 50% in hypothyroid L
V and was normalized by T-3 treatment. In contrast, SERCA2 protein in atria
was unaltered in the hypothyroid state. PLB protein expression significant
ly increased by 1.6- and 5-fold in the hypothyroid LV and atria, respective
ly, and returned to euthyroid levels with T-3 treatment. Expression of NCX
protein showed a greater response to T-3 treatment in atria tissue than in
ventricular tissue. Sarcoplasmic reticulum calcium cycling is determined in
part by the ratio of SERCA2 to PLB. This ratio was sixfold higher in the a
tria compared with LV, suggesting that PLB may play a minor role in the reg
ulation of SERCA2 function in normal atria. We conclude that calcium transp
orter proteins are responsive to thyroid hormone in a chamber-specific mann
er, with atria showing a greater change in protein content in response to T
-3. The differential effect on atria may account for the occurrence of atri
al rather than ventricular arrhythmias in response to even mild degrees of
thyrotoxicosis.