Intracellular guanosine-5'-O-(2-thiodiphosphate) alters the dynamics of receptor-mediated responses in bullfrog sympathetic neurons.
The mechanism by which intracellularly applied guanosine-5'-O-(2-thiodiphosphate) alters responses to chicken II luteinizing hormone-releasing hormone, muscarine, and substance P in bullfrog sympathetic neurons was examined. Whole-cell recordings were made from enzymatically dissociated single neurons. Guanosine-5'-O-(2-thiodiphosphate) was applied intracellularly by adding it to the pipette solution with fixed amounts of GTP. Guanosine-5'-O-(2-thiodiphosphate) did not affect the proportion of cells that responded to any of the agonists. Guanosine-5'-O-(2-thiodiphosphate) decreased the amplitude of the responses to submaximal concentrations of agonist. At maximal concentrations of agonist, guanosine-5'-O-(2-thiodiphosphate) did not decrease the response to the first application of agonist; however, with guanosine-5'-O-(2-thiodiphosphate) intracellularly, successive responses to maximal concentrations of agonist were decreased in amplitude and increased in time course. Intracellular guanosine-5'-O-(2-thiodiphosphate) did not accelerate the rate or magnitude of desensitization to substance P. A kinetic model of receptor-guanine nucleotide-binding protein (G protein) coupling predicts that a decrease in the available G protein pool should decrease both the magnitude and the time course of the build-up of active G proteins. The results are consistent with the hypothesis that guanosine-5'-O-(2-thiodiphosphate) binds tightly to G proteins, thereby effectively decreasing the available G protein pool with repeated agonist applications.
Simmons
M A
MA
Department of Pharmacology, Marshall University, Huntington, West Virginia 25755-9310.
Mather
R J
RJ
D000818:Animals; D019204:GTP-Binding Proteins / Q000378:metabolism; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology; D006153:Guanosine Diphosphate / Q000031:analogs & derivatives* / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D066298:In Vitro Techniques; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects; D009116:Muscarine / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D011892:Rana catesbeiana; D011956:Receptors, Cell Surface / Q000187:drug effects / Q000378:metabolism*; D013373:Substance P / Q000494:pharmacology; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D013873:Thionucleotides / Q000378:metabolism*
D011956:Receptors, Cell Surface; D013873:Thionucleotides; D006153:Guanosine Diphosphate; D013373:Substance P; D007987:Gonadotropin-Releasing Hormone; C023427:guanosine 5'-O-(2-thiodiphosphate); D009116:Muscarine; D006160:Guanosine Triphosphate; D019204:GTP-Binding Proteins