Inhibition of Ca2+ accumulation in isolated sarcoplasmic reticulum by thyroid hormones

Varda Shoshan-Barmatz, Asher Shainberg

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    6 Scopus citations

    Abstract

    Thyroid hormones inhibit Ca2+ accumulation and ATPase activity of isolated sarcoplasmic reticulum vesicles. Half-maximal inhibition was obtained by about 2.5 μM. The ATP hydrolysis activity of the purified (Ca2+ + Mg2+)-ATPase or the SR vesicles, in the presence of the Ca2+ ionophore A23187, is not inhibited by T3 or T4. Modification of T3 or T4 in the ring portion, but not in the amino portion, of te molecules results in T4 and T3 analogues which are unable to inhibit Ca2+ accumulation. T3 and T4 have no significant effect on various partial reactions of the transport cycle such as: the binding of ATP and Ca2+, or ADP-ATP exchange and E-P formation from ATP, but they inhibit the E-P formation from inorganic phosphate (Pi) and ATP-Pi exchange. The inhibition of both Ca2+ accumulation and ATPaseactivity by T3 or T4 is increased in the presence of Pi. Binding sites for [125I]T3 and for [125I]T4 in SR proteins were demonstrated using either equilibrium dialysis or gel overlay techniques. The results suggest that the thyroid hormones inhibit the ATP-dependent Ca2+ accumulation, probably by inhibiting the transport of anions which act as the Ca2+ precipitating anion.

    Original languageEnglish
    Pages (from-to)82-88
    Number of pages7
    JournalBiochimica et Biophysica Acta - Biomembranes
    Volume1065
    Issue number1
    DOIs
    StatePublished - 31 May 1991

    Bibliographical note

    Funding Information:
    This researcwh ass upporteidn part by the Fund for BasicR esearcahd ministerebdy the IsraeliA cademico f Sciencea ndH umanitiesW. e thankP rof. D.H. MacLen-nan for the hospitaliteyx tendetdo us and for enabling us to perfo__rm_p_a rtof these experimeinnt sh is laboratory and Mrs. R. Shamif or here xpertt echnicaal ssis-tance.

    Keywords

    • Calcium ion accumulation
    • Sarcoplasmic reticulum
    • Thyroxine

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