Thyroid hormone enhances Ca2+ pumping activity of the cardiac sarcoplasmic reticulum by increasing Ca2+ ATPase and decreasing phospholamban expression.
Phospholamban is a putative suppressor of the Ca2+ ATPase of the cardiac sarcoplasmic reticulum. The level of mRNA encoding the Ca2+ ATPase has been shown to be increased, whereas the phospholamban mRNA level to be decreased in the ventricles obtained from hyperthyroid rabbits [Nagai R, Zarain-Herzberg A. Brandl CJ, Fujii J. Tada M. MacLennan DH, Alpert NR, Periasamy M. (1989) Proc Natl Acad Sci USA 86: 2966-2970]. The present study was designed to examine whether these effects of thyroid hormone on the expression of the Ca2+ ATPase and phospholamban are exerted directly on cardiac myocytes and whether the resultant incoordinate expression of these proteins alters Ca2+ pumping activity. We studied the levels of phospholamban and Ca2+ ATPase mRNA in primary isolated neonatal rat myocardial cells incubated with triiodothyronine (T3) for 3-48 h and the Ca2+ uptake activity of the microsomes prepared from the cells. Northern blot analysis showed that T3 decreased phospholamban mRNA levels to about a half of control in 24 h. On the other hand, Ca2+ ATPase mRNA gradually increased with time. EC50 for phospholamban mRNA expression was 2.5 x 10(-10) M which was approximately 10 times higher than that for the Ca2+ ATPase. T3 increased Vmax of Ca2+ uptake with the significant reduction of K0.5 for Ca2+ (0.40 +/- 0.02 microM for control v 0.31 +/- 0.02 microM for T3-treated vesicles), indicating that thyroid hormone stimulates Ca2+ pumping activity not only by increasing the Ca2+ ATPase but also decreasing phospholamban. These results suggested that phospholamban regulates the Ca2+ ATPase in dual modes; in short time range, by decreasing the affinity of the Ca2+ ATPase for Ca2+ by phosphorylation of phospholamban with cAMP-dependent protein kinase, and in long time range, by changing the molecular ratio between the two proteins through the regulation of gene expression.
Kimura
Y
Y
Department of Medicine and Pathophysiology, Osaka University Medical School, Japan.
Otsu
K
K
Nishida
K
K
Kuzuya
T
T
Tada
M
M
D000818:Animals; D000831:Animals, Newborn; D001483:Base Sequence; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000235:genetics / Q000378:metabolism; D000252:Calcium-Transporting ATPases / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D017931:DNA Primers / Q000235:genetics; D015870:Gene Expression / Q000187:drug effects; D006321:Heart / Q000187:drug effects*; D066298:In Vitro Techniques; D017136:Ion Transport / Q000187:drug effects; D008861:Microsomes / Q000187:drug effects / Q000378:metabolism; D008969:Molecular Sequence Data; D009206:Myocardium / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D014284:Triiodothyronine / Q000494:pharmacology*; D000099211:Phospholamban
D002118:Calcium; D002135:Calcium-Binding Proteins; D000252:Calcium-Transporting ATPases; D017931:DNA Primers; D012333:RNA, Messenger; D014284:Triiodothyronine; D000099211:Phospholamban