Characterization of alpha 1-adrenergic receptor subtypes linked to iodide efflux in rat FRTL cells.
We have characterized alpha 1-adrenergic receptor subtypes in functional rat thyroid cells, FRTL, with relation to iodide efflux, and have also examined the effect of TSH on alpha 1 receptor subtypes. FRTL cells grown in a medium containing 5 mU TSH/ml (6H cells) had five times the number of alpha 1 receptors of those maintained in TSH-free medium (5H cells) (11.2 fmol/10(6) cells compared with 2.0 fmol/10(6) cells). Pretreatment with chlorethylclonidine (CEC; 10 mumols/l), which inactivates only alpha 1b receptors, caused 98.8% and 97.0% decreases in the density of specific [3H]prazosin-binding sites in 5H and 6H cells respectively. LIGAND computer program analysis of the displacement curves for 2-(2,6-dimethoxyphenoxyethyl)-aminomethyl-1,4 benzodioxane (WB4101) showed that FRTL cells contained mostly low-affinity WB4101 sites. Using the phenoxybenzamine inactivation method, we found a linear relationship between alpha 1 receptor density and the cytosolic free Ca2+ concentration response in FRTL cells. Pre-exposure of intact FRTL cells to CEC caused a 98.7% decrease in noradrenaline-stimulated maximal increase in cytosolic free Ca2+. Also, CEC and 3,4,5-trimethoxy-benzoic acid 8-(diethylamino) octyl ester (TMB-8), but not nicardipine, inhibited noradrenaline-stimulated iodine efflux. The results suggest that FRTL cells contain mostly the alpha 1b-adrenergic receptor subtype; that the alpha 1b receptors mediate cytosolic free Ca2+ and iodide efflux responses, and that TSH enhances these responses by increasing the alpha 1b receptor density without affecting the post-receptor mechanism.
Shimura
H
H
Third Department of Internal Medicine, University of Yamanashi Medical School, Japan.
Endo
T
T
Tsujimoto
G
G
Watanabe
K
K
Hashimoto
K
K
Onaya
T
T
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D003000:Clonidine / Q000031:analogs & derivatives / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D007454:Iodides / Q000378:metabolism*; D009638:Norepinephrine / Q000494:pharmacology; D010643:Phenoxybenzamine / Q000494:pharmacology; D011224:Prazosin / Q000378:metabolism; D051381:Rats; D011942:Receptors, Adrenergic, alpha / Q000032:analysis* / Q000187:drug effects / Q000378:metabolism; D013961:Thyroid Gland / Q000166:cytology / Q000378:metabolism*; D013997:Time Factors
D007454:Iodides; D011942:Receptors, Adrenergic, alpha; D010643:Phenoxybenzamine; C051731:chlorethylclonidine; D003000:Clonidine; D002118:Calcium; D009638:Norepinephrine; D011224:Prazosin