A TSH/dibutyryl cAMP activated Cl-/I- channel in FRTL-5 cells.
An iodide (I) and chloride (Cl) channel has been identified in the continuously cultured FRTL-5 thyroid cell line using a cell attached patch clamp technique. The channel is activated by TSH and dibutyryladenosine cyclic monophosphate (Bt2-cAMP) but not by phorbol 12-myristate 13-acetate (TPA). Gluconate can not replace chloride or iodide and the channel is impermeable to Na+,K+ and tetraethylammonium ions. The current-voltage relationship demonstrates that the single channel current is a linear function of the clamp voltage. Single channel currents reversed at a pipette potential close to 0 mV. The mean single channel conductance was 60 pS for Cl- and 50 pS for I-. From the I-V relationship there was a strong outward rectification with Cl-, and a complete block with I-, in the single channel current above +40 mV. The feature of the channel is manifested in the single channel records by four distinct, equally spaced conductance levels. We suggest the channel is important for the transport of I and Cl ions across the apical membrane into the colloid space and is important for hormone synthesis and follicle formation.
Yoshida
A
A
First Department of Internal Medicine, Tottori University School of Medicine, Nishimachi 36-1, Yonago, 683, Japan.
Hattori
K
K
Hisatome
I
I
Taniguchi
S
S
Ueta
Y
Y
Hukui
H
H
Santo
Y
Y
Igawa
O
O
Shigemasa
C
C
Kosugi
S
S
Grollman
E F
EF
D000818:Animals; D003994:Bucladesine / Q000494:pharmacology*; D015220:Calcium Channels / Q000502:physiology*; D002478:Cells, Cultured; D007455:Iodine / Q000502:physiology*; D007473:Ion Channels / Q000502:physiology*; D018408:Patch-Clamp Techniques; D051381:Rats; D013755:Tetradecanoylphorbol Acetate / Q000378:metabolism; D013961:Thyroid Gland / Q000378:metabolism; D013972:Thyrotropin / Q000378:metabolism*
D015220:Calcium Channels; D007473:Ion Channels; D003994:Bucladesine; D013972:Thyrotropin; D007455:Iodine; D013755:Tetradecanoylphorbol Acetate