Isoproterenol enhances a calcium-independent potassium current in mouse anterior pituitary tumor cells.
1. The patch-clamp technique was used to study the action of the beta-adrenergic agonist (-)-isoproterenol in anterior pituitary tumor cells of the mouse. 2. (-)-Isoproterenol induced an inward-rectifying potassium conductance with half-maximal stimulation at a concentration of approximately 67 nM. The isomer (+)-isoproterenol was less effective in stimulating the current. 3. The effect of (-)-isoproterenol was abolished by cholera toxin treatment, indicating the involvement of a Gs protein, whereas pertussis toxin treatment did not exhibit a current reduction. 4. We blocked or stimulated phosphorylation pathways in cells to test the involvement of adenosine 3',5'-cyclic monophosphate (cAMP). It was concluded that the current stimulation probably was not exclusively mediated by cAMP. 5. Activation of calcium-dependent potassium channels by an isoproterenol-induced calcium influx into the cell could be excluded. 6. Therefore it is suggested that the observed activation of a potassium current by isoproterenol could be directly mediated by a Gs protein.
Weik
R
R
Department of Molecular Neuroendocrinology, Max Planck Institute for Experimental Medicine, Goettingen, Federal Republic of Germany.
Spiess
J
J
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000502:physiology*; D002772:Cholera Toxin / Q000494:pharmacology; D004837:Epinephrine / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000494:pharmacology; D007545:Isoproterenol / Q000494:pharmacology*; D051379:Mice; D037342:Pertussis Toxin; D010903:Pituitary Gland, Anterior / Q000378:metabolism*; D010911:Pituitary Neoplasms / Q000378:metabolism*; D015221:Potassium Channels / Q000187:drug effects*; D014407:Tumor Cells, Cultured / Q000378:metabolism; D010566:Virulence Factors, Bordetella / Q000494:pharmacology
D015221:Potassium Channels; D010566:Virulence Factors, Bordetella; D015124:8-Bromo Cyclic Adenosine Monophosphate; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D002772:Cholera Toxin; D037342:Pertussis Toxin; D019204:GTP-Binding Proteins; D007545:Isoproterenol; D002118:Calcium; D004837:Epinephrine