Triiodothyronine affects the electrical properties of GH3 cells.

Electrophysiological experiments show that T3 has a direct effect on the cell membrane of GH3 cells, a transformed line from the rat pituitary. Slope conductance versus membrane potential, resting membrane resistance, potential, capacity and action potentials were measured in this study. Using a current clamp technique, the effects of tetrodotoxin, tetraethylammonium, apamin, and nifedipine were measured and compared with those directly evoked by T3. T3 increased the slope conductance: 1. at around -60 mV, as did tetrodotoxin (Na+ channel blocker); 2. at about -40 mV, as did nifedipine (Ca2+ channel blocker), but decreased this conductance strongly between -20 and -30 mV, as did both nifedipine and apamin (Ca2(+)-sensitive K+ channel blocker). Action potentials were inhibited by T3 and by nifedipine. Action potentials in these cells are primarily related to Ca2+ ions. It seems that T3 inhibits the Ca2+ current and, as a consequence, the Ca2(+)-sensitive K+ current.