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A kinetic model of the effect of agonist and anesthetics on ligand-gated ion channels, developed in earlier work, is further refined and used to predict traces observed in fast-perfusion electrophysiological studies on recombinant GABAA receptors under a wide range of agonist and/or anesthetic concentrations. The model incorporates only three conformational states (resting, open, and desensitized) but allows for the modulation of the conformational free energy landscape connecting these states resulting from adsorption of agonist and/or anesthetic to the bilayer in which the protein is embedded. The model is shown to reproduce the diverse and complex features of experimental traces remarkably well, including both anesthetic-induced and agonist-induced traces, as well as the modulation of agonist-induced traces by anesthetic, either coapplied or continuously present. The solutions to the kinetic equations, which give the time-dependence of each of the nine protein states (three ligation states for each of the three conformations), describe the flow of probability among these states and thus reveal the kinetic underpinnings of the traces. Many of the parameters in the model, such as the desorption rate constants of anesthetic and agonist, are directly related to model-independent experimental measurements and thus can serve as a definitive test of its validity.

Dietary modulation of cancer & cancer biomarkers. Dietary item or component studied: indole-3-carbinol (I3C)Outcome studied: lung tumor multiplicity. Study type: mice resulting from reciprocal crosses between B6129 SF1/J [AHR(b-1/d)] and 129Sv/ImJ [AHR(d/d)] mice. Tissue/biological material/sample size: heart, thymus, lung, spleen, liver, kidney, abnormal lymph node, testes or ovaries, colon and skinMode of exposure: dibenzo[a,l]pyrene (DBP) was administered to pregnant mice (15 mg/kg, gavage) on gestation day 17, and 2000 p.p.m. indole-3-carbinol (I3C) was fed to half of the mice from gestation day 9 until weaning. Impact on outcome (including dose-response): Offspring born to dams fed I3C exhibited markedly fewer mortalities (P < 0.0001). Maternal dietary exposure to I3C also significantly lowered lung tumor multiplicity (P = 0.035) in offspring surviving to 10 months of age. The I3C chemoprotection was independent of either maternal or fetal AHR genotype. The bioavailability of DBP to fetal target tissue was demonstrated by assessing DNA covalent adduction with a (33)P-post-labeling assay. The bioavailability of I3C was determined by dosing a subset of pregnant mice with [(14)C]-I3C. KEYWORD CLASSIFICATION: administration & dosage;analysis;Animals;antagonists & inhibitors;Anticarcinogenic Agents;Benzopyrenes;Biological Availability;chemically induced;Diet;dietary modulation of cancer & cancer biomarkers;DNA Adducts;Female;Fetal Diseases;humans;Indoles;Liver Neoplasms,Experimental;Lung;Lung Neoplasms;Lymphoma;Male;Maternal-Fetal Exchange;metabolism;Mice;mortality;NF-kappa B;nursing;pharmacokinetics;Pregnancy;prevention & control;Research;toxicity;Toxicology; The fetus and neonate are sensitive targets for chemically induced carcinogenesis. Few studies have examined the risk/benefit of chemoprotective phytochemicals, given in the maternal diet, against transplacental carcinogenesis. In this study, B6129 SF1/J (AHR(b-1/d)) and 129Sv/ImJ (AHR(d/d)) mice were cross-bred. The polycyclic aromatic hydrocarbon, dibenzo[a,l]pyrene (DBP), was administered to pregnant mice (15 mg/kg, gavage) on gestation day 17, and 2000 p.p.m. indole-3-carbinol (I3C), a chemoprotective phytochemical from cruciferous vegetables, was fed to half of the mice from gestation day 9 until weaning. Offspring born to dams fed I3C exhibited markedly fewer mortalities (P < 0.0001). Maternal dietary exposure to I3C also significantly lowered lung tumor multiplicity (P = 0.035) in offspring surviving to 10 months of age. The I3C chemoprotection was independent of either maternal or fetal AHR genotype. The bioavailability of DBP to fetal target tissue was demonstrated by assessing DNA covalent adduction with a (33)P-post-labeling assay. The bioavailability of I3C was determined by dosing a subset of pregnant mice with [(14)C]-I3C. Addition of chemoprotective agents to the maternal diet during pregnancy and nursing may be an effective new approach in reducing the incidence of cancers in children and young adults.

The time- and concentration-dependence of agonist-induced ion currents through postsynaptic receptors is often remarkably complex, as is the modulation of these currents by other solutes such as anesthetics. Traditionally, kinetic models have been developed that involve agonist binding and conformational transitions among a manifold of protein conformational states engineered to reproduce the complexity of the electrophysiological results. In the present work, an alternative model is proposed that minimizes the number of conformational states while additionally incorporating effects of adsorption of agonist and nonbinding compounds such as anesthetics to the bilayer in which these intrinsic membrane proteins are embedded. Adsorption of these aqueous solutes alters bilayer physical properties, which in turn can distort the protein conformational free energy landscape, and thus alter the rate constants of protein conformational transitions. The complexity of the predicted ion currents then arises from the time-dependence of solute adsorption, resulting in strongly time-dependent transition rate “constants”. If only nonbinding solutes are present, the model simplifies considerably. Best fits with respect to a small set of parameters of the predicted current traces are found to be in excellent agreement with previously measured currents in GABAA receptors induced by a broad range of supraclinical concentrations of isoflurane and sevoflurane.