title: Reevaluation of the electrophysiological actions of thyrotropin-releasing hormone in a rat pituitary cell line (GH3).
abstract: The electrophysiological actions of TRH were examined in the clonal pituitary cell line GH3 with the use of the perforated patch variation of the standard whole cell patch-clamp technique. The action of TRH on spontaneously spiking cells was to cause a brief hyperpolarization (first phase action), followed by a period during which action potential behavior was significantly modified (second phase action). The modifications during second phase action included a reduction in the slope of the up-stroke, a reduced peak potential, an increase in duration, and a depolarizing shift of the after-hyperpolarization. The modification of voltage- and calcium-dependent conductances that underlie these changes were investigated in voltage clamp experiments. During first phase action TRH was found to increase calcium-dependent potassium current. During second phase action TRH was found to significantly reduce the L-type calcium current (35%), with no alteration in the T-type calcium current. The second phase action of TRH on calcium-dependent potassium conductance was complex. First, a decrease was observed. This was followed by an increase that did not become fully manifest until after TRH was washed from the cell. TRH caused no change in voltage-dependent potassium current. These results indicate that the second phase action of TRH on action potential behavior in GH3 cells is mediated by a reduction in L-type calcium current and alterations in the behavior of calcium-dependent potassium currents, but not through changes in voltage-dependent potassium currents.
authors.affiliation: Department of Physiology, School of Medicine and Biomedical Sciences, State University of New York, Buffalo 14214.
authors.forename: S M
authors.initials: SM
authors.lastname: Simasko
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002460:Cell Line; D004553:Electric Conductivity; D004594:Electrophysiology; D010902:Pituitary Gland / Q000187:drug effects / Q000502:physiology*; D015221:Potassium Channels / Q000502:physiology; D051381:Rats; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology*
chemical_list: D015221:Potassium Channels; D013973:Thyrotropin-Releasing Hormone; D002118:Calcium