Protein phosphatase 2A reverses inhibition of inward rectifying K+ currents by thyrotropin-releasing hormone in GH3 pituitary cells.
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 Ca2+ 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-2Ac) but not PP-1c 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 GH3 cell excitability.
Barros
F
F
Departamento de Biología Funcional, Facultad de Medicina, Universidad de Oviedo, Spain.
Mieskes
G
G
del Camino
D
D
de la Peña
P
P
D000255:Adenosine Triphosphate / Q000494:pharmacology; D000266:Adenylyl Imidodiphosphate / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002460:Cell Line; D002772:Cholera Toxin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism / Q000494:pharmacology; D004533:Egtazic Acid / Q000494:pharmacology; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D010749:Phosphoprotein Phosphatases / Q000494:pharmacology*; D010911:Pituitary Neoplasms; D026902:Potassium Channel Blockers; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology*; D054648:Protein Phosphatase 2; D051381:Rats; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology*; D013997:Time Factors
D026902:Potassium Channel Blockers; D015221:Potassium Channels; D000266:Adenylyl Imidodiphosphate; D004533:Egtazic Acid; D013973:Thyrotropin-Releasing Hormone; D000255:Adenosine Triphosphate; D002772:Cholera Toxin; D000242:Cyclic AMP; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2; D002118:Calcium