Amitriptyline inhibits the G protein and K+ channel in the cloned thyroid cell line

Abstract We have reported that thyroid K + channel is activated by extracellular application of the thyroid-stimulating hormone (TSH) using single channel recording method performed on cloned normal rat thyroid cell (FRTL-5) membrane. Treatment of dibutyryladenosine cyclic monophosphate (Bt 2 cAMP) also activated the TSH-dependent K + channel. These findings indicate that the thyroid K + channel is activated through the TSH-adenosine cyclic monophosphate (cAMP)-protein kinase A system. We examined the effects of amitriptyline on TSH-guanosine triphosphate binding protein (G protein)-adenylate cyclase-cAMP-K + channel system in the cloned normal rat thyroid cell line FRTL-5. Amitriptyline inhibited the cAMP production induced by TSH. Amitriptyline also inhibited the cAMP production induced by cholera toxin, indicating that amitriptyline inhibited the thyroid G protein. Amitriptyline had no effect on TSH-receptor binding and cAMP production by forskolin (adenylate cyclase stimulator). Amitriptyline inhibited the K + channel activation by cAMP, indicating that the suppressing mechanism is not the inhibition of TSH receptor or G protein but the direct suppression of K + channel. It was concluded that amitriptyline inhibited the thyroid G protein and K + channel.