Effect of thyroxine on calcium distribution in rat thymocytes in vitro.
Chlorotetracycline (CTC) was used as a fluorescent Ca2+-sensitive probe to study the redistribution of intracellular membrane-bound Ca2+ in thyroxine (T4)-treated rat thymocytes. Incubation of thymocytes in the Ca2+-supplemented medium in the presence of 1-100 nM T4 for 30 min resulted in a twofold increase in the amount of EGTA-accessible plasma membrane-bound Ca2+ as compared to that in the Ca2+-free medium. The induced decrease in CTC fluorescence was more pronounced with the occurrence of respiration and oxidative phosphorylation in inhibitors. The mitochondrial Ca2+ pool was shown to increase. The nonmitochondrial Ca2+ pool decreased after a 30-min incubation in the presence of 1 nM T4 and increased when 100 nM T4 was used under the same conditions. Without incubation, different concentrations of T4 stimulated the decrease in the Ca2+ pool of the endoplasmic reticulum (ER) compared to the control cells, which was demonstrated using inhibitors of the ER Ca2+-ATPase (vanadate, BHQ). Calmodulin blockers (triftazin and R24) caused a significant decrease (over 50%) in CTC fluorescence in the T4-treated thymocytes. This suggests that T4 can act as an in vitro stimulator of calmodulin-dependent Ca2+ accumulation in thymocyte membranes. The results of our experiments with AlF4- suggest that T4 stimulates the activity of G-proteins by a receptor-mediated mechanism.
Sukocheva
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Institute of Physiology and Biophysics, Academy of Sciences of Uzbekistan, Tashkent. pusman@biophys.apc.org
Gizatullina
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Gagelgans
A I
AI
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002478:Cells, Cultured; D004533:Egtazic Acid / Q000378:metabolism / Q000494:pharmacology; D051381:Rats; D013950:Thymus Gland / Q000166:cytology / Q000378:metabolism*; D013974:Thyroxine / Q000378:metabolism*
D004533:Egtazic Acid; D013974:Thyroxine; D002118:Calcium