Differences in the electrophysiological response to I- and the inhibitory anions SCN- and ClO-4, studied in FRTL-5 cells.
The electrophysiological properties of the Na+/I- symporter (NIS) were examined in a cloned rat thyroid cell line (FRTL-5) using the whole-cell patch-clamp technique. When the holding potential was between -40 mV and -80 mV, 1 mM NaI and NaSCN induced an immediate inward current which was greater with SCN- than with I-. The reversal potential for I- and SCN- induced membrane currents was +50 mV. This is close to the value of +55 mV calculated by the Nernst equation for Na+. These results are consistent with I- and SCN- translocation via the NIS that is energized by the electrochemical gradient of Na+ and coupled to the transport of two or more Na+. There was no change in the membrane current recording with ClO-4 indicating that ClO-4 was either not transported into the cell, or the translocation was electroneutral. ClO-4 addition, however, did reverse the inward currents induced by I- or SCN-. These effects of I-, SCN- and ClO-4 on membrane currents reflect endogenous NIS activity since the responses duplicated those seen in CHO cells transfected with NIS. There were additional currents elicited by SCN- in FRTL-5 cells under certain conditions. For example at holding potentials of 0 and +30 mV, 1 mM SCN- produced an increasingly greater outward current. This outward current was transient. In addition, when SCN- was washed off the cells a transient inward current was detected. Unlike SCN-, 1-10 mM I- had no observable effect on the membrane current at holding potentials of 0 and +30 mV. The results indicate FRTL-5 cells may have a specific SCN- translocation system in addition to the SCN- translocation by the I- porter. Differences demonstrated in current response may explain some of the complicated influx and efflux properties of I-, SCN- and ClO-4 in thyroid cells.
Yoshida
A
A
First Department of Internal Medicine, Tottori University School of Medicine, Yonago 683, Japan. ayoshida@grape.med.tottori-u.ac.jp
Sasaki
N
N
Mori
A
A
Taniguchi
S
S
Ueta
Y
Y
Hattori
K
K
Tanaka
Y
Y
Igawa
O
O
Tsuboi
M
M
Sugawa
H
H
Sato
R
R
Hisatome
I
I
Shigemasa
C
C
Grollman
E F
EF
Kosugi
S
S
D000818:Animals; D016466:CHO Cells; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D002704:Chlorates / Q000378:metabolism; D006224:Cricetinae; D007455:Iodine / Q000378:metabolism*; D008564:Membrane Potentials; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D051381:Rats; D027981:Symporters; D013861:Thiocyanates / Q000378:metabolism*; D013961:Thyroid Gland; D014162:Transfection; D000099209:Sodium-Iodide Symporters
D002352:Carrier Proteins; D002704:Chlorates; D007455:Iodine; D008565:Membrane Proteins; D027981:Symporters; D013861:Thiocyanates; D000099209:Sodium-Iodide Symporters; C024553:sodium thiocyanate; C032706:sodium chlorate