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Calcium is transported into the lumen of pig thyroid follicles by fluid phase basolateral to apical transcytosis
Author(s) -
Fonlupt Pierre,
Audebet Christine,
Gire Veronique,
BernierValentin Francoise,
Rousset Bernard
Publication year - 1997
Publication title -
journal of cellular physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.529
H-Index - 174
eISSN - 1097-4652
pISSN - 0021-9541
DOI - 10.1002/(sici)1097-4652(199704)171:1<43::aid-jcp6>3.0.co;2-h
Subject(s) - thyroglobulin , chemistry , lucifer yellow , thyroid , calcium , apical membrane , lumen (anatomy) , transcytosis , apical cell , kinetics , medicine , biophysics , endocrinology , biochemistry , biology , membrane , cell , intracellular , endocytosis , physics , organic chemistry , quantum mechanics , gap junction
The lumen of thyroid follicles contains a high concentration of thyroglobulin, the thyroid prohormone and a high concentration of calcium (Ca 2+ ). As thyroglobulin binds Ca 2+ , intraluminal Ca 2+ is expected to be in free and protein‐bound forms. In the present work, we have investigated the mechanism(s) by which Ca 2+ could enter the lumen of thyroid follicles. 45 Ca 2+ uptake studies were carried out on reconstituted pig thyroid follicles (RTF) and pig thyroid cell monolayers (TCM) in primary culture, representing experimental systems with two compartments (cells + lumina) and one compartment, respectively. 45 Ca 2+ accumulation in RTF was rapid during the first hour of incubation and then slowly increased. Analysis of the uptake data with a “two compartments” model gave two kinetic constant values: k ‐1 = 1.71 ± 0.28 hr ‐1 and k ‐2 = 0.20 ± 0.05 hr ‐1 (n = 10). The slow uptake process accounted for 20–50% of the total RTF‐associated Ca 2+ after 24 hr. 45 Ca 2+ uptake by TCM was rapid and reached a stable level within 1–2 hr. Experimental data fitted with a “single compartment” model and gave a k ‐1 value of 1.64 ± 0.15 hr ‐1 (n = 10) which was not statistically different from the k ‐1 obtained for 45 Ca 2+ uptake by RTF. We then compared the kinetics of 45 Ca 2+ uptake by RTF with the kinetics of transport of fluid phase markers: [ 14 C]‐sucrose and Lucifer Yellow from the medium to the lumen of RTF. [ 14 C]‐sucrose and Lucifer Yellow uptakes by RTF appeared as slow processes compatible with the entry in a single compartment with k ‐1 values of 0.32 ± 0.06 hr ‐1 (n = 3) and 0.23 ± 0.015 hr ‐1 (n = 3), respectively. These values were not significantly different from the k ‐2 value obtained for 45 Ca 2+ uptake by RTF. These data suggest that thyroid follicles would possess two independent Ca 2+ compartments: cells and lumen, and that the entry of Ca 2+ into the lumen of follicles probably could take place by fluid phase basolateral to apical transcytosis. J. Cell. Physiol. 171:43–51, 1997. © 1997 Wiley‐Liss, Inc.