PubMed · 2801872
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T J Zimmerman, U Dukar, G F Nardin, R Patchett, M Fuqua. 1989-10-15. Carbachol dose response.. https://doi.org/10.1016/s0002-9394(14)73323-9
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A stable cell line derived from a human oligodendroglioma (HOG) was used to study the regulation of muscarinic- and histamine receptor-mediated phosphoinositide hydrolysis. Both carbachol and histamine increased inositol monophosphate (InsP) accumulation in a dose- and time-dependent manner in the presence of lithium and the effect of simultaneous addition of carbachol and histamine was additive, implying independent signal transduction pathways. Homologous desensitization of muscarinic, but not histamine receptors, could be demonstrated although neither receptor type appeared to be heterologously desensitized. [3H]InsP accumulation in HOG cells was also stimulated by fluoride, suggesting guanosine triphosphate (GTP)-binding protein involvement, but phosphoinositide (PtdIns) hydrolysis was not sensitive to pertussis toxin. Phorbol ester-activation of protein kinase C (PKC) inhibited both muscarinic and histamine receptor-stimulated InsP release but did not attenuate either the fluoride-induced release of InsP nor beta-adrenergic receptor-mediated stimulation of adenylate cyclase activity. Taken together, we conclude that muscarinic and histamine receptors are differentially regulated through both PKC-dependent and -independent mechanisms, and that feedback inhibition of PtdIns turnover occurs proximal to the GTP binding proteins.
We studied desensitization of nicotinic acetylcholine (ACh) receptor channels in the clonal BC3H-1 cell line. We measured the current response to rapid perfusion of outside-out patches with 1 microM to 5 mM ACh, carbamylcholine and suberyldicholine. After binding to the receptors and opening the ion channels, all agonists induce a rapid, concentration-dependent decay of channel activity. The time constant of the current decay ranged from several seconds at low agonist concentrations to about 50 ms at saturating concentrations. The decay rate at saturating concentrations was independent of voltage. The ratio of steady-state to peak current ranged from 0.5 at low agonist concentrations to 0.02 or less at high concentrations. The rate of recovery from desensitization after removal of agonist was also measured. For ACh, the recovery time constant was 320 ms; recovery from desensitization by carbamylcholine was twice as fast. A linear kinetic results. The data are consistent with a cyclic model, although, it is not possible to uniquely determine all of the rate constants in this scheme. The results are compared with competitive binding and single channel studies of desensitization in BC3H-1 cells.
Mast cells are hypothesized to participate in processes leading to tissue fibrosis in human lung and skin. To explore the possible involvement of mast cell mediators in fibrogenesis, the mitogenic activity of mast cell tryptase from human lung was examined in vitro. The results indicate that human tryptase is a potent inducer of DNA synthesis in fibroblasts from multiple sources, including human lung. As demonstrated by mitogenic responses in fibroblasts, but not in vascular smooth muscle cells, tryptase is a mitogen with target cell specificity. Additionally, specificity is demonstrated by the differences in mitogenic activity of tryptase in comparison with thrombin, a structurally related mitogenic proteinase. Examination of the mitogenic effects of tryptase in the presence of other mitogens reveals synergy with mitogens that act through receptors coupled to intrinsic tyrosine kinases (insulin, epidermal growth factor, and basic fibroblast growth factor) or to G proteins (thrombin and serotonin). In the latter case, studies in Chinese hamster lung fibroblasts using specific receptor agonists and antagonists or receptor-transfected cell lines reveal a requirement for the activation of a G protein (Gi) negatively coupled to adenylate cyclase to act synergistically with tryptase. These data establish that human tryptase is a potent and specific mitogen in vitro and suggest that mitogenic signals generated by tryptase can interact synergistically with signals generated by both tyrosine kinase-coupled and G protein-coupled growth factor receptors.