Integrity of the occluding barrier in high-resistant thyroid follicular epithelium in culture. II. Immediate protective effect of TSH on paracellular leakage induced by Ca2+ removal and cytochalasin B.
The acute influence of thyrotropin (TSH) on the Ca2+ and cytoskeleton dependence of the thyroid epithelial occluding barrier was investigated in porcine thyrocyte monolayers cultured on filter support. The barrier function was assayed by measurements of the transepithelial resistance (RTE) and the apicobasal flux (FTE) of radiotracers (125I-; [3H]inulin) as well as by morphological examination of junctions (fluorescein isothiocyanate-phalloidin labeling of F-actin; electron microscopy). Removal of extracellular Ca2+ (Ca2+e) by ethylene glycol-bis(beta-aminoethyl ether) N,N,N',N'-tetraacetic acid (EGTA) rapidly decreased RTE and increased FTE of both radiotracers. These changes were inhibited by TSH (1 mU/ml) given 6 min before Ca2+e removal. The inhibitory effect was total when Ca2+e was removed from the basal medium and partial when the cultures were totally deprived of Ca2+e. TSH added 10 min after basal depletion of Ca2+e partially reversed the changes in RTE and FTE. TSH also potentiated the recovery of RTE and FTE seen after readdition of Ca2+e. In contrast to Ca2+e-depleted cultures, the distribution of F-actin at the level of the junctional complex as well as the junctional ultrastructure were normal in cultures stimulated with TSH before depletion. TSH was also found to abolish the paracellular leakage induced by cytochalasin B (50 microM). TSH per se did not influence FTE of radiotracers. The observed effects of TSH were in all respects reproduced by forskolin (50 microM). In conclusion, acute stimulation with TSH protects the barrier function of porcine thyrocyte monolayers from the otherwise deleterious influence of Ca2+e-chelating and microfilament-disruptive agents. This effect of TSH is mediated by cyclic AMP. The data indicate that the integrity of the thyroid occluding barrier not only remains but is strengthened in TSH-stimulated cultures. The possible involvement of cell adhesion molecules in this response to TSH is discussed.
Nilsson
M
M
Department of Anatomy, University of Göteborg, Sweden.
Mölne
J
J
Ericson
L E
LE
D008841:Actin Cytoskeleton / Q000187:drug effects; D000199:Actins / Q000302:isolation & purification; D000818:Animals; D001692:Biological Transport; D002118:Calcium / Q000494:pharmacology*; D016764:Cell Polarity / Q000502:physiology; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000031:analogs & derivatives; D003571:Cytochalasin B / Q000494:pharmacology*; D004533:Egtazic Acid / Q000494:pharmacology; D004848:Epithelium / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure; D007365:Intercellular Junctions / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D008856:Microscopy, Fluorescence; D013552:Swine; D013961:Thyroid Gland / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D013972:Thyrotropin / Q000494:pharmacology*
D000199:Actins; D005576:Colforsin; D003571:Cytochalasin B; D004533:Egtazic Acid; D013972:Thyrotropin; D000242:Cyclic AMP; D002118:Calcium