Changes in membrane potential of cultured porcine and human thyroid cells in response to thyrotrophin and other agents.

Thyrotrophin (TSH), cyclic AMP, cyclic GMP and 1-methyl-3-isobutyl-xanthine (MIX) promoted the reassociation of isolated porcine and human thyroid cells into follicular structures in culture and stimulated the uptake of radio-iodide. Monolayer cells were present in all cultures, but in decreasing proportions as the concentration of stimulator was increased. The resting membrane potential of porcine thyroid cells cultured for 4 days in the presence of TSH was -54 +/- 3.6 (mean +/- S.D.) mV for follicular cells and -31 +/- 2.6 mV for monolayer cells. In the absence of TSH, only monolayer cells were present and their membrane potential was -24 +/- 2.0 mV. Removal of hormone by washing resulted in hyperpolarization to -70 +/- 2.9 mV (follicular cells) or -59 +/- 3.4 mV (monolayer cells). Subsequent replacement of TSH, or addition of cyclic AMP, MIX, prostaglandin E1 (PGE1) or long-acting thyroid stimulator immunoglobulin resulted in depolarization of previously hyperpolarized cells, to approximately the membrane potential observed before washing. Incubation in MIX resulted in enhanced sensitivity to the depolarizing effect of TSH. Cells cultured in the absence of TSH were unresponsive to TSH or other stimulators. The membrane potential of human thyroid cells behaved similarly in response to TSH, to hormone removal and replacement, and to MIX and PGE1.