Inhibitors of 1,2-diacylglycerol kinase potentiate the TRH-induced stimulation of Ca2+-activated K+ current.
Transient activation of the outward K+ current caused by a rise in the cytosolic free Ca2+ concentration, [Ca2+]i was the predominant change in plasma membrane ion flux during the first phase of thyrotropin-releasing hormone (TRH) action on pituitary cells. Following the intracellular application of inhibitors of 1,2-diacylglycerol (DG) kinase, R59022 and 1-oleyl-2-acetyl glycerol (OAG) the outward K+ current response to TRH in cells of the pituitary line GH3B6 was potentiated. This potentiation was analyzed further with the combination of microfluorimetric and electrophysiological recording techniques. Receptor-induced changes in [Ca2+]i and ion channel activation were monitored simultaneously in the same cell. It was found that R59022 and OAG altered in parallel the TRH-induced transient rise in [Ca2+]i and outward K+ current. This resulted in a significant correlation between the kinetic parameters (speed of onset, duration) of the [Ca2+]i and the K+ current responses to TRH. Intracellular application of vanadate abolished the rapid start of the TRH response presumably by its block of Ca2+ uptake into the endoplasmic reticulum, leading to depletion of a Ca2+ pool mobilizable by inositol 1,4,5-trisphosphate (Ins(1,4,5)P3). The use of vanadate unmasked a slowly developing response to TRH, which was still potentiated by OAG and R59022. Together, these observations suggest that Ca2+ mobilization during the first phase of TRH action is mediated by two distinct processes, one of which is linked to receptor stimulation of DG production.
Mollard
P
P
Laboratoire de Neurophysiologie, UA CNRS 1200, Bordeaux, France.
Vacher
P
P
Dufy
B
B
Winiger
B P
BP
Schlegel
W
W
D002118:Calcium / Q000494:pharmacology*; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism; D002999:Clone Cells / Q000187:drug effects / Q000378:metabolism; D019852:Diacylglycerol Kinase; D010770:Phosphotransferases / Q000037:antagonists & inhibitors*; D010972:Platelet Activating Factor / Q000037:antagonists & inhibitors; D015221:Potassium Channels / Q000187:drug effects*; D011744:Pyrimidinones / Q000494:pharmacology; D013844:Thiazoles / Q000494:pharmacology; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology*; D014638:Vanadates / Q000494:pharmacology
D015220:Calcium Channels; D010972:Platelet Activating Factor; D015221:Potassium Channels; D011744:Pyrimidinones; D013844:Thiazoles; D014638:Vanadates; D013973:Thyrotropin-Releasing Hormone; C047505:R 59022; D010770:Phosphotransferases; D019852:Diacylglycerol Kinase; D002118:Calcium