title: Stimulation of calcium-ATPase activity by 3,5,3'-tri-iodothyronine in rat thymocyte plasma membranes. A possible role in the modulation of cellular calcium concentration.
abstract: We have previously demonstrated that 3,5,3'-tri-iodo-L-thyronine (T3) produces a very rapid and transient increase in calcium uptake and cytoplasmic free calcium concentration in the rat thymocyte, and have postulated that Ca2+-ATPase may contribute to the overall effect of T3 on cellular calcium metabolism. In the present study, we show that in the rat thymocyte, T3 increased plasma membrane Ca2+-ATPase activity. This effect of T3 was very rapid, seen at 30 s after the addition of the hormone, and was concentration-related, evident at a physiological concentration as low as 1 pM. Evaluation of the effect of several thyronine analogues on Ca2+-ATPase activity revealed the following order of potency: D-T3 greater than or equal to 3'-isopropyl-L-T2 = L-T3 = L-T4 = D-T4 greater than L-rT3 greater than 3,5-L-T2 greater than DL-thyronine. Studies with the calmodulin antagonist trifluoperazine demonstrated that thymocyte Ca2+-ATPase activity and its stimulation by T3 are influenced by calmodulin. Other studies showed that several adrenergic agents, agonists and antagonists, had no effect on thymocyte Ca2+-ATPase activity and its stimulation by T3. From these and previous observations, we would suggest that in the rat thymocyte, the T3-induced increase in Ca2+-ATPase activity, which enhances the expulsion of calcium from the cell, plays a role in the diminution and transiency of the stimulatory effect of T3 on thymocyte calcium metabolism.
authors.affiliation: Hubert H. Humphrey Center for Experimental Medicine and Cancer Research, Hebrew University-Hadassah Medical School, Jerusalem, Israel.
authors.forename: J
authors.initials: J
authors.lastname: Segal
authors.forename: J
authors.initials: J
authors.lastname: Hardiman
authors.forename: S H
authors.initials: SH
authors.lastname: Ingbar
mesh_terms: D000818:Animals; D002118:Calcium / Q000032:analysis*; D000252:Calcium-Transporting ATPases / Q000378:metabolism*; D002147:Calmodulin / Q000037:antagonists & inhibitors; D002395:Catecholamines / Q000494:pharmacology; D002462:Cell Membrane / Q000187:drug effects / Q000201:enzymology; D005260:Female; D051381:Rats; D011919:Rats, Inbred Strains; D013950:Thymus Gland / Q000187:drug effects* / Q000201:enzymology / Q000648:ultrastructure; D014268:Trifluoperazine / Q000494:pharmacology; D014284:Triiodothyronine / Q000494:pharmacology*
chemical_list: D002147:Calmodulin; D002395:Catecholamines; D014284:Triiodothyronine; D014268:Trifluoperazine; D000252:Calcium-Transporting ATPases; D002118:Calcium