Imidazoline binding sites on PC12 cells and bovine chromaffin cells.
Stimulating actions of imidazolines on the adrenal medulla were demonstrated by several laboratories. As only a few data about signal transduction exist, the aim of the present study is to establish a cellular model on which both subtypes of imidazoline receptors are present. Binding studies using [3H]clonidine for I1-sites and [3H]idazoxan for I2-sites were performed on bovine chromaffin cells and a PC12 cell line. The intracellular calcium signal was determined by a Fura-2 signal using a fluorescence microscope. Both subtypes of imidazoline binding sites are present on either crude membrane fractions, purified plasma membranes, and mitochondrial membranes of the adrenal medulla. Although the density of I1- and I2-sites on the plasma membrane fraction is almost equal, on the mitochondrial membrane fraction Bmax of I2-binding sites was double that of the I1-binding number. An increase in intracellular calcium signal could be obtained during stimulation of chromaffin cells by various I1- and I2-receptor modulators. Because a saturation of I2-binding could not be obtained in PC12 cells, adrenal medullary chromaffin cells may be a more suitable model for investigating imidazoline receptor signal transduction.
Steffen
G
G
Institute of Pharmacology, Medical University of Lübeck, Germany.
Dendorfer
A
A
Dominiak
P
P
D000313:Adrenal Medulla / Q000378:metabolism*; D058669:Adrenergic alpha-2 Receptor Antagonists; D000317:Adrenergic alpha-Antagonists / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D002417:Cattle; D002462:Cell Membrane / Q000378:metabolism; D002837:Chromaffin Granules; D003000:Clonidine / Q000378:metabolism*; D004146:Dioxanes / Q000378:metabolism*; D019329:Idazoxan; D007093:Imidazoles / Q000378:metabolism*; D054755:Imidazoline Receptors; D008928:Mitochondria / Q000378:metabolism; D016716:PC12 Cells; D051381:Rats; D018341:Receptors, Adrenergic, alpha-2 / Q000378:metabolism*; D011955:Receptors, Drug / Q000378:metabolism*; D015398:Signal Transduction
D058669:Adrenergic alpha-2 Receptor Antagonists; D000317:Adrenergic alpha-Antagonists; D004146:Dioxanes; D007093:Imidazoles; D054755:Imidazoline Receptors; D018341:Receptors, Adrenergic, alpha-2; D011955:Receptors, Drug; D003000:Clonidine; D019329:Idazoxan