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[The significance of the radioactive isotope potassium-40 for the normal development of the animal organism].

21-day-old rats subjected to nourishing by KCl (20-30 mg per day) without radioactive isotope 40K. Besides the decrease of 40K content in animal tissue (30-50%) a reducing of body weight was obtained. In the second set of experiments in the lead (9 cm thick) chamber with low (20 times) background radiation the trustworthy decrease of young mouse development was observed under the simultaneous reducing other components of background radiation (radon, products of its disintegration, gamma, beta radiation, cosmic radiation). Possible mechanisms of necessity of 40K natural concentration for the normal development of the animal organism are discussed.

Animals↗

An isotopic rubidium ion efflux assay for the functional characterization of nicotinic acetylcholine receptors on clonal cell lines.

An isotopic rubidium ion efflux assay has been developed for the functional characterization of nicotinic acetylcholine receptors on cultured neurons. This assay first involves the intracellular sequestration of isotopic potassium ion analog by the ouabain-sensitive action of a sodium-potassium ATPase. Subsequently, the release of isotopic rubidium ion through nicotinic acetylcholine receptor-coupled monovalent cation channels is activated by application of nicotinic agonists. Specificity of receptor-mediated efflux is demonstrated by its sensitivity to blockade by nicotinic, but not muscarinic, antagonists. The time course of agonist-mediated efflux, within the temporal limitations of the assay, indicates a slow inactivation of receptor function on prolonged exposure to agonist. Dose-response profiles (i) have characteristic shapes for different nicotinic agonists, (ii) are described by three operationally defined parameters, and (iii) reflect different affinities of agonists for binding sites that control receptor activation and functional inhibition. The rubidium ion efflux assay provides fewer hazards but greater sensitivity and resolution than isotopic sodium or rubidium ion influx assays for functional nicotinic receptors.

Animals↗