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Protein phosphatase 2A reverses inhibiton of inward rectifying K + currents by thyrotropin‐releasing hormone in GH 3 pituitary cells
Author(s) -
Barros Francisco,
Mieskes Gottfried,
del Camino Donato,
de la Peña Pilar
Publication year - 1993
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(93)80851-k
Subject(s) - pipette , chemistry , medicine , dephosphorylation , endocrinology , thyrotropin releasing hormone , cholera toxin , intracellular , anterior pituitary , phosphatase , biophysics , phosphorylation , hormone , biochemistry , biology
Thyrotropin‐releasing hormone (TRH) reduces an inwardly rectifying K + current in whole‐cell voltage‐clamped GH3 rat anterior pituitary cells. The TRH effect depends on the maintenance of a background level of Ca 2+ in the pipette buffer, and is rapidly minimized by the intracellular dialysis produced under whole‐cell conditions. Introduction of ADP‐NH‐P, a non‐hydrolizable ATP analog, in the pipettes, nearly abolishes the TRH‐evoked inhibition. The TRH‐induced reduction of the inwardly rectifying current is significantly enhanced by incubation of cells 2–4 h with cholera toxin, but not by inclusion of 1 mM cyclic AMP in the pipettes. Under control whole‐cell conditions, the reduction caused by TRH is not reversed upon washout of the neuropeptide. However, this effect is readily reversed by addition of purified catalytic subunits of protein phosphatase 2A (PP‐2A c ) but not PP‐1 c to the buffer used to fill the patch pipettes. Among previous results with PP inhibitors, these data indicate that PP2A is involved in the phosphorylation/dephosphorylation mechanism(s) that regulate the delayed TRH effects on GH 3 cell excitability.