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Results for “Potassium Isotopes”

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At least 19 recordsLinked to original sources
PubMed1988

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↗
PubMed1989

The effects of cromakalim on the detrusor muscle of human and pig urinary bladder.

The effects of cromakalim, a potassium channel activating drug, have been studied on isolated detrusor muscle strips from normal Landrace boar, normal and unstable mini-pig and unstable human bladder. Cromakalim abolished spontaneous activity in all strips but did not abolish the ability of the detrusor muscle from any of the specimens studied to respond to carbachol, increased extracellular K+ or transmural nerve stimulation. Intravenous infusion of cromakalim in the urethral obstructed mini-pig caused the characteristic unstable contractions associated with bladder outflow obstruction to be abolished, leaving the animal able to void. Experiments with potassium isotopes and the sucrose gap technique demonstrated that cromakalim increased the potassium permeability and hyperpolarised the cell membrane, consistent with its reported actions on other smooth muscles. These results suggest that drugs such as cromakalim, which act by reducing membrane excitability without inhibiting responses to existing innervation, may have a clinical application in the treatment of instability which is secondary to bladder outflow obstruction.

Animals↗
PubMed1986

Flux ratio of valinomycin-mediated K+ fluxes across the human red cell membrane in the presence of the protonophore CCCP.

The ratio of valinomycin-mediated unidirectional K+ fluxes across the human red cell membrane, has been determined in the presence of the protonophore carbonylcyanide m-chlorophenylhydrazone, CCCP, using the K+ net efflux and 42K influx. The driving force for the net efflux (Vm - EK+) has been calculated from the membrane potential, estimated by the CCCP-mediated proton distribution and the Nernst potential for potassium ions across the membrane. An apparent driving potential for the K+ net efflux has been calculated from the K+ flux ratio, determined in experiments where the valinomycin and CCCP concentrations were varied systematically. This apparent driving force, in conjunction with the actual driving force calculated on basis of the CCCP estimated membrane potential, is used to calculate a flux ratio exponent, which represents an estimate of the deviation of valinomycin-mediated K+ transport from unrestricted electrodiffusion, when protonophore is present. In the present work, the flux ratio exponent is found to be 0.90 when the CCCP concentration is 5.0 microM and above, while the exponent decreases to about 0.50 when no CCCP is present. The influence of CCCP upon the rate constants in the valinomycin transport cycle is discussed. The significance of this result is that red cell membrane potentials are overestimated, when calculated from valinomycin-mediated potassium isotope fluxes, using a constant field equation.

Carbonyl Cyanide m-Chlorophenyl Hydrazone↗
PubMed1975

Radionuclides and the patient with coronary artery disease.

The emergence in the past 20 years of nuclear medicine as a distinct diagnostic discipline has been a major clinical advance. The relatively rapid evolution from the small laboratory limited primarily to the study of thyroid disease to the large unit in which radioactive tracers (radionuclides) are utilized to evaluate structure and function of most organ systems has been accelerated by major advances in instrumentation, new radioactive tracers and application of computer techniques. Application of these radionuclide techniques to the study of coronary artery disease has been quite recent, and has in part been limited by the need for a coordinated effort between the cardiologist and the specialist in nuclear medicine. However, realization of the potential usefulness of these techniques has fostered an increasingly productive liaison between the two specialties. The potential advantages of these radionuclides in evaluating patients with cardiovascular disease is twofold: first, they may permit the noninvasive or atraumatic acquisition of data that might otherwise be obtained only at the time of cardiac catheterization; second, and perhaps more important, they may permit the acquisition of physiologic measurements or observations not attainable by more conventional modes of study. Functionally, these techniques can be divided into those that evaluate cardiac performance and those that evaluate coronary blood flow, regional myocardial perfusion and myocardial viability.

Cesium↗