Differences in the electrophysiological response to I − and the inhibitory anions SCN ∮- and C1O 4−, studied in FRTL-5 cells

Abstract

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 C1O 4 − indicating that C1O 4 − was either not transported into the cell, or the translocation was electroneutral. C1O 4 − addition, however, did reverse the inward currents induced by I − or SCN −. These effects of I −, SCN − and C1O 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 C1O 4 − in thyroid cells.