Measurements of membrane potentials in Escherichia coli K-12 inner membrane vesicles with the safranine method.

The use of safranine, a positively-charged dye, as a probe for the determination of membrane potentials in Escherichia coli vesicles has been studied. 1. Shifts in the spectrum of safranine were observed during induction of potassium ion diffusion potentials with valinomycin or during oxidation of formate by vesicles prepared from cells of E.

Thermodynamic aspects of translocation of reducing equivalents by mitochondria.

The "poise" in which there is no net transport of reducing equivalents mediated by glutamate and aspartate movements across the mitochondrial membrane has been studied using nonrespiring liver mitochondria, supplied with a given extramitochondrial ATP/ADP ratio. Absorbance shifts in safranine have been used as a probe to estimate the membrane potential generated under these conditions. Measurements of the asymmetric distribution of substrate anions and of reducing potential across the limiting membrane gave estimated differences of between 2.

The effect of transition from traditional to urban life-style on the insulin secretory response in Australian Aborigines.

Recent epidemiologic studies have revealed a high prevalence of maturity-onset diabetes in certain populations that have undergone comparatively rapid urbanization. There is evidence suggesting that Australian Aborigines may respond to urbanization in this way. Thirteen full-blood Aborigines from the Mowanjum Community, Derby, Western Australia, cooperated in the present study.

Induction of exocytosis from glomus cells by incubation of the carotid body of the rat with calcium and ionophore A23187.

Carotid bodies from adult rats were electron microscopically studied after incubation in glucose-containing salt solutions containing calcium and/or ionophore A23187 or neither. In the absence of the ionophore, adding or omitting calcium had no effect on the fine structure of the glomus cells. Incubation in the medium containing both 1 mM calcium and the ionophore caused the appearance of exocytotic membrane profiles in several glomus cells.

Measurements of membrane potentials using the dye safranine.

A metachromatic shift in the spectrum of the cationic dye safranine occurs upon induction of electrical potentials across the mitochondrial membrane by adding respiratory substrate, ATP or a cation conductor valinomycin (when a potassium gradient exists across the membrane) to a mitochondrial suspension. The extent of spectral change correlates linearily to the membrane potential. During the spectral change safranine is taken up by the mitochondria and most of the dye can be recovered in the pellet after centrifugation.

Changes in membrane potential during calcium ion influx and efflux across the mitochondrial membrane.

1. A depolarisation of the membrane of rat liver mitochondria, as measured with the safranine method, is seen during Ca2+ uptake. The depolarisation is followed by a slow repolarisation, the rate of which can be increased by the addition of EGTA or phosphate.

Effect of cations on the temperature sensitivity of Ca2+ transport in rat-liver mitochondria and safranine uptake by liposomes.

The activation energy of mitochondrial Ca2+ transport has been studied in various conditions by Arrhenius plots in the temperature range 6-20 degrees C. In the presence of Mg2+ the activation energy is decreased to 18 kJ/mole from that of 40 kJ/mole found in a sucrose medium. In the presence of the polyamine spermine the activation energy is practically 0 kJ/mole.

Effect of propranolol and related drugs on transmembraneous pH differences in liposomes.

Propranolol (1-isopropylamino-3-(1-naphtoloxy)-propan-2-ol) a beta-adrenergic receptor blocking agent was found to cause changes of transmembraneous pH in liposomes prepared from Soy-lecithin and cardiolipin. When the external pH was neutral and the internum of the liposomes acidic, the drug decreased the pH gradient. When the externum was acidic and the internum neutral, the gradient was increased by the drug.

Effect of Mg2+ and spermine on the kinetics of Ca2+ transport in rat-liver mitochondria.

Plots relating the initial rate of mitochondrial Ca2+ transport to the Ca2+ concentration (kinetic plots) have a hyperbolic shape in a Ca2+ concentration range of 2.5-100 muM as measured in sucrose or KCl media. In the presence of Mg2+ or a polyamine spermine, which both are competitive inhibitors of Ca2+ binding to low affinity sites at the membrane surface, the shape of the plots becomes sigmoidal.

Effect of inhibitors on the sigmoidicity of the calcium ion transport kinetics in rat liver mitochondria.

The kinetic plot (initial rate of Ca2+ transport versus concentration) of mitochondrial Ca2+ transport is hyperbolic in a sucrose medium. The plot becomes sigmoidal in the presence of competitive inhibitors of Ca2+ binding to low affinity sites of the membrane surface such as Mg2+ and K+. The plot also becomes sigmoidal in the presence of Ba2+.

Stacking of safranine in liposomes during valinomycin-induced efflux of potassium ions.

Liposomes were prepared from phosphatidylcholine and cardiolipin in a KCl medium and suspended in a choline chloride medium with safranine. When efflux of K+ was induced by valinomycin, spectral shifts characteristic of stacking were observed. Ca2+ inhibited the rate of stacking in a competitive manner with a Ki of about 200 muM, while La3+ was about 10 times more potent.