Okadaic acid and calyculin A enhance the effect of thyrotropin-releasing hormone on GH3 rat anterior pituitary cells excitability.
Thyrotropin-releasing hormone (TRH) causes a transient hyperpolarization followed by several minutes of increased action potential frequency in patch-perforated current-clamped GH3 cells. Treatment of cells for 5 min with either 2 or 100 nM of the protein phosphatase inhibitor okadaic acid does not affect electrical activity of the cells, but potentiates the enhancement of action potential frequency elicited by a subsequent addition of TRH. Alternatively, 100 nM (but not 2 nM) of okadaic acid added during the second phase of TRH action, further increases the frequency of firing above that produced by the hormone. Similar effects to those of 2 nM okadaic acid are observed with 20 nM calyculin A. These data suggest that a protein phosphatase plays a major role in regulating the delayed effects of TRH on cell excitability in GH3 cells.
Delgado
L M
LM
Departamento de Biología Funcional, Facultad de Medicina, Universidad de Oviedo, Spain.
de la Peña
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P
del Camino
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D
Barros
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F
D000200:Action Potentials / Q000187:drug effects*; D000818:Animals; D002478:Cells, Cultured; D004988:Ethers, Cyclic / Q000494:pharmacology*; D007476:Ionophores / Q000494:pharmacology; D008387:Marine Toxins; D008839:Microelectrodes; D019319:Okadaic Acid; D009991:Oscillometry; D010080:Oxazoles / Q000494:pharmacology*; D010903:Pituitary Gland, Anterior / Q000187:drug effects*; D051381:Rats; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology*
D004988:Ethers, Cyclic; D007476:Ionophores; D008387:Marine Toxins; D010080:Oxazoles; D019319:Okadaic Acid; D013973:Thyrotropin-Releasing Hormone; C059041:calyculin A