Membrane Effects of Thyrotropin-Releasing Hormone and Estrogen Shown by Intracellular Recording from Pituitary Cells

The effects of thyrotropin-releasing hormone and 17 β-estradiol on the electrical membrane properties of a prolactin-secreting pituitary cell line (GH 3 /B6) were studied with intracellular microelectrode recordings. Of the cells tested, 50 percent were excitable and displayed calcium-dependent action potentials when depolarized. When injected directly on the membrane of an excitable cell, thyrotropin-releasing hormone and 17 β-estradiol induced action potentials within 1 minute. The spiking activity was preceded by a progressive increase of the input resistance without any detectable change in the resting membrane polarization. The results reveal a rapid effect of both substances on the membrane of GH 3 /B6 cells. In the case of thyrotropin-releasing hormone, which has both a short-term effect on release of prolactin and a long-term effect on its synthesis, the induced electrical activity may be associated with the stimulation of prolactin production. The physiological implication of 17 β-estradiol-induced, calcium-dependent spiking activity remains to be elucidated.