Differential transmembrane diffusion of triiodothyronine and thyroxine in liposomes: regulation by lipid composition

CHEHÍN, R.; ISSÉ, B.; RINTOUL M.R.; FARÍAS R.N

JOURNAL OF MEMBRANE BIOLOGY

Springer-Verlag New York

Año: 1999 vol. 167 p. 251 - 256

0022-2631

How thyroid hormones move across biological or model membranes is a subject of controversy. The passage of the 3,5,3´triiodo l-thyronine and 3,5,3´,5´ tetraiodo l-thyronine across model membranes was evaluated by the addition of the hormones to liposomes containing 2, 4,6-trinitrobenzene sulfonic acid. Results indicate that hormones can react with an amino-reactive compound pre-encapsulated into phosphatidylcholine liposomes. The transversal motions of thyroid hormones were characterized by using physiological concentration levels of (125I) 3,5,3´triiodo l-thyronine and (125I) 3,5,3´,5´ tetraiodo l-thyronine. The hormone distribution between the two monolayers was time-dependent and kinetic data were fitted to a single exponential. Results obtained show that 3,5,3´ triiodo l-thyronine can permeate phospholipid membranes and the diffusion time increases in the gel and liquid-ordered phase. On the contrary, 3,5,3´, 5´ tetraiodo l-thyronine could not diffuse the liposomal membrane from dimyristoyl and dipalmitoyl phosphatidylcholine in gel phase and egg yolk phosphatidylcholine:cholesterol in the liquid-ordered phase. Our results in the liquid-ordered phase suggest that diffusion movement of thyroid hormones across cell membranes depends on the amount of cholesterol in the bilayer.