Ligand Binding Kinetics of Substance P and Neurokinin A Receptors Stably Expressed in Chinese Hamster Ovary Cells and Evidence for Differential Stimulation of Inositol 1,4,5-Trisphosphate and Cyclic AMP Second Messenger Responses |
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Authors: | Yasuo Takeda Paul Blount Bruce S Sachais rew D Hershey Rita Raddatz James E Krause |
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Institution: | Department of Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, Missouri 63110. |
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Abstract: | Stably transfected Chinese hamster ovary cells expressing either the substance P receptor or neurokinin A receptor were constructed, isolated, and characterized. Equilibrium ligand binding studies performed on whole cells demonstrated that cell lines expressing either of these receptors contained a single class of high-affinity binding sites with an apparent KD of 0.16 nM for the substance P receptor and an apparent KD of 2.1 nM for the neurokinin A receptor. The higher affinity of substance P for its receptor was accounted for by both a greater association rate constant and a lesser dissociation rate constant. The time course and extent of ligand-stimulated inositol 1,4,5-trisphosphate mass increases in both cell lines were similar and displayed rapid and transient kinetics. Ligand-stimulated cyclic AMP accumulation was also apparent in the cell lines, although the time course and magnitude of the responses were substantially different, with the neurokinin A receptor mediating a greater and more prolonged response. These studies establish the presence of functional substance P receptors and neurokinin A receptors in the stably transfected cell lines and provide evidence for agonist-dependent differential stimulation of second messenger responses. |
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Keywords: | Substance P receptor Neurokinin A receptor Tachykinins Chinese hamster ovary cells Differential stimulation Second messenger responses Inositol 1 4 5-trisphosphate Cyclic AMP |
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