Thyroid hormones and active calcium transport of inside-out red cell membrane vesicles.

Thyroid hormones may influence the active transport of Ca2+ across the cell membrane. To test the physiologic relevance of this mechanism, we used inside-out human red cell membrane vesicles as a model of the cell membrane Ca2+ pump. We monitored by spectrophotometric methods the kinetics of the uptake of Ca2+ in the presence of 10(-5)-10(-10) M thyroid hormones or their analogues. Vesicles freed of calmodulin and protein inhibitor(s) of the Ca2+ pump were also obtained. The results are as follows: (1) Thyroxine inhibits the active Ca2+ uptake; (2) this effect antagonizes that of soluble calmodulin; and (3) triiodothyronine and other analogues of the thyroid hormones are less active than thyroxine. We conclude that the thyroid hormones may influence cell Ca2+ homeostasis by direct action on the Ca2+ pump.

[Influence of nutrition, age and vitamin D status on fasting urinary excretion of calcium in postmenopausal women]. / Influenza della nutrizione, dell'età e dell'assetto vitaminico D sull'escrezione urinaria del calcio a digiuno nelle donne in menopausa.

The purpose of the present study was to evaluate the influence of nutrition, age, and Vitamin D status on fasting urinary calcium (Ca) as a function of creatinine excretion (Ca/Cr) and of glomerular filtration rate (Ca/GFR) in postmenopausal women. Fasting urinary calcium, urinary Cr and GFR were measured in 18 women aged 54 to 91 years before and after six days of a calcium (400 mg/die) and sodium (100 mEq/die) restricted diet with a controlled content of proteins, lipids and glucides. Aged (over 64 y.) women having an adequate vitamin D status showed fasting urinary Ca/Cr and Ca/GFR after the controlled diet significantly lower than those showed before. It is concluded that fasting Ca/Cr and Ca/GFR may be nutrition-dependent. A revision of the significance of the fasting urinary Ca excretion is consequently suggested.