In vitro effects of thyroid hormones on red blood cell Ca++ -dependent ATPase activity

Thyroid hormones (TH) have been shown to exert a direct stimulatory effect on the Ca++-dependent ATPase from human and other mammalian erythrdcytes. In this in vitro system, T4 has been shown to be more effective than T3. In the present study, TH effects on Ca++-dependent ATPase were investigated, using rabbit and human erythrocyte membranes, after preincubation with 10−10M T4, in the presence or in the absence of exogenous calmodulin (CaM) (5.10−12M to 5.10−9 M). Ca++-dependent ATPase activity was measured as inorganic phosphate (Pi) release from 1 mM ATP. The results showed that basal Ca++-dependent ATPase activity in rabbits was moderately increased by T4 (1.44 ± 0.05 vs 1.32 ± 0.04 μmol Pi/mg protein/90 min, mean ± SE; p