Thyrotropin releasing hormone stimulation of prolactin release. Evidence for a membrane potential-independent, Ca2+-dependent mechanism of action.
Thyrotropin releasing hormone (TRH) and high extracellular K+ induce prolactin release from rat pituitary cells (GH3 cells) in culture. TRH, as well as high K+ (50 mM), was shown to increase 45Ca2+ efflux from these cells. The effects of TRH and high K+ on membrane polarization was determined indirectly using the lipophilic cation, triphenylmethyl phosphonium ion (TPMP+). The resting membrane potential of GH3 cells was -50 +/- 1.7 mV. TRH, which induced a marked increase in 45Ca2+ efflux and stimulated prolactin release, had no effect on membrane polarization measured simultaneously. High K+, which also increased 45Ca2+ efflux and prolactin release, depolarized the GH3 cell as evidenced by a marked increase in [3H]TPMP+ efflux. These results suggest that TRH and high K+ may act via different mechanisms to increase intracellular Ca2+ and stimulate prolactin release.
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D010911:Pituitary Neoplasms; D011188:Potassium / Q000494:pharmacology; D011388:Prolactin / Q000378:metabolism*; D051381:Rats; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology*
D013973:Thyrotropin-Releasing Hormone; D011388:Prolactin; D011188:Potassium; D002118:Calcium