Fast-activating cation channel in barley mesophyll vacuoles. Inhibition by calcium

In contrast to the vacuolar ion channels which are gated open by an increase of cytosolic Ca²⁺ the vacuolar ion currents at resting cytosolic Ca²⁺are poorly explored. Therefore, this study was performed to investigate the properties of the so-called fast-activating vacuolar (FV) current which dominates the electrical characteristics of the tonoplast at physiological free Ca²⁺ concentrations. Patch—clamp measurements were performed on whole barley ( Hordeum vulgare ) mesophyll vacuoles and on excised tonoplast patches. Single ion channels were identified, which, based on their selectivity, activation kinetics, Ca²⁺- and voltage-dependence, carry the whole-vacuole FV current. Reversal potential determinations indicated a K⁺ overs C⁻ permeability ratio of about 30. Both inward and outward whole-vacuole currents as well as the activity of single FV channels were inhibited by an increase of cytosolic Ca²⁺, with a K_d≈ 6 µM. At physiological vacuolar Ca²⁺ activities, the FV channel is an outward-rectifying potassium channel. The FV channel was activated in less than a few milliseconds both by negative and positive potential steps, having a minimal activity that is 40 mV negative of the K⁺ equilibrium potential. It is proposed that transport of K⁺ through this cation channel controls the electrical potential difference across the tonoplast.     

Oleic Acid Inhibits Gap Junction Permeability and Increases Glucose Uptake in Cultured Rat Astrocytes

Abstract: The role of oleic acid in the modulation of gap junction permeability was studied in cultured rat astrocytes by the scrape-loading/Lucifer yellow transfer technique. Incubation with oleic acid caused a dose-dependent inhibition of gap junction permeability by 79.5% at 50 µ M , and no further inhibition was observed by increasing the oleic acid concentration to 100 µ M . The oleic acid-mediated inhibition of gap junction permeability was reversible and was prevented by bovine serum albumin. The potency of oleic acid-related compounds in inhibiting gap junction permeability was arachidonic acid > oleic acid > oleyl alcohol > palmitoleic acid > stearic acid > octanol > caprylic acid > palmitic acid > methyloleyl ester. Oleic acid and arachidonic acid, but not methyloleyl ester, increased glucose uptake by astrocytes. Neither oleic acid nor arachidonic acid increased glucose uptake in the poorly coupled glioma C6 cells. These results support that the inhibition of gap junction permeability is associated with the increase in glucose uptake. We suggest that oleic acid may be a physiological mediator of the transduction pathway leading to the inhibition of intercellular communication.     

Vasomotor instability preceding tilt-induced syncope: does respiration play a role?

Lipsitz, Lewis A., Raymond Morin, Margaret Gagnon, DanKiely, and Aharon Medina. Vasomotor instability precedingtilt-induced syncope: does respiration play a role? J. Appl. Physiol. 83(2): 383-390, 1997.This studyaimed to determine whether alterations in cardiovascular dynamicsbefore syncope are related to changes in spontaneous respiration.Fifty-two healthy subjects underwent continuous heart rate (HR),arterial blood pressure (BP), and respiratory measurements during10-min periods of spontaneous and paced breathing (0.25 Hz) in thesupine and 60° head-up tilt positions. Data were evaluated by powerspectrum and transfer function analyses. During tilt, 27 subjectsdeveloped syncope or presyncope and 25 remained asymptomatic. Subjectswith tilt-induced syncope had significantly greater increases inlow-frequency (0.04-0.15 Hz) systolic BP, diastolic BP, and HRpower during tilt than the asymptomatic subjects(P  0.01). This difference waspresent during spontaneous but not paced breathing. However, averagetidal volume, respiratory rate, minute ventilation, proportion ofbreaths below 0.15 Hz, and low-frequency respiratory power during tilt did not differ between syncopal and nonsyncopal subjects. Transfer magnitudes between low-frequency respiration and BP, and between BP andinterbeat interval, were also similar between groups. Thus vasomotorinstability before syncope is not related to alterations in respirationor the cardiovagal baroreflex but may reflect oscillating centralsympathetic outflow to the vasculature.

     

Functional Morphology of the Introvert and Digestive System of Myzostoma cirriferum (Myzostomida)

Myzostoma cirriferum feeds by diverting food particles carried by the ambulacral grooves of its comatulid host Antedon bifida. When searching for food, the myzostome uses its protrusible introvert to fulfil two major functions: sensory perception and the capture of food particles. The digestive system is composed of four parts, viz. a pharynx, that is contained within the introvert, a stomach, a series of paired caeca and an intestine that lie in the myzostome's trunk. The pharynx is supplied with a thick muscle which, thanks to peristaltic movements, carries food particles from the mouth to the stomach. Both stomach and caecal cells are able to absorb dissolved nutriments and to store lipids, whereas intestinal cells are only capable of absorption. Due to the beating of their cilia, stomach cells also carry food particles into the caecal lumen, where they are subjected to endocytosis and intracellular digestion by caecal cells. Undigested food fragments eventually gather in a very large, apical vacuole, and the cell apices containing vacuoles are eliminated into the caecal lumen by an apocrinal process. Detached cell apices reach the stomach, where they are embedded in a matrix, together forming a spindle-shaped faecal mass that is expelled through the postero-ventral anus. The observed digestive process—entailing the regular elimination of the apical part of the caecal digestive cells—appears to be unique among the Spiralia.     

Characterization of Nine Novel Mutations in the CD40 Ligand Gene in Patients with X-Linked Hyper IgM Syndrome of Various Ancestry

X-linked immunodeficiency with hyper-IgM (HIGMX-1) is a rare disorder caused by defective expression of the CD40 ligand (CD40L) by activated T lymphocytes, resulting in inefficient T-B cell cooperation and failure of B cells to undergo immunoglobulin isotype switch. In the present work, we describe nine patients of various ancestry who bear different mutations in the X chromosome–specific CD40L gene. Two of the mutations were nonsense mutations, one each resulting in premature stop codons at amino acid residues 39 and 140. Three patients had single point missense mutations, one each at codons 126, 140, and 144. Another patient had a 4-bp genomic deletion in exon 2, resulting in a frameshift and premature termination. Three patients showed insertions, one each of 1, 2, and 4 nt, probably because of polymerase slippage, resulting in frameshift mutation and premature termination. Overall, these observations confirm the heterogeneity of mutations in HIGMX-1. However, the identification of two patients whose mutation involves codon 140 (previously shown to be altered in two other unrelated subjects) suggests that this may be a hotspot of mutation in HIGMX-1. In two additional patients with clinical and immunological features indistinguishable from canonical HIGMX-1, no mutation was detected in the coding sequence, in the 5' flanking region, or in the 3' UTR.     

Interaction of influenza virus proteins with planar bilayer lipid membranes II. Effects of rimantadine and amantadine

The dependence of the surface potential difference (ΔU), transversal elasticity module (E₁) and membrane conductivity (G₀) on the concentrations of the antiviral drugs, rimantadine and amantadine was studied in the planar bilayer lipid membrane system. The method used was based on independent measurements of the second and third harmonics of the membrane capacitance current. The binding constants of bilayer lipid membranes obtained from the drug adsorption isotherms were 2.1 · 10⁵ M^?1 and 1.3 · 10⁴ M^?1 for rimantadine and amantadine, respectively. The changes in G₀ took place only after drug adsorption saturation had been achieved. The influence of rimantadine and amantadine on the interaction of bilayer lipid membranes with matrix protein from influenza virus was also investigated. The presence of 70 μg/ml rimantadine in the bathing solution resulted in an increase in the concentration of M-protein at which the adsorption and conductance changes were observed. The effects of amantadine were similar to those of rimantadine but required a higher critical concentration of amantadine. The results obtained suggest that the antiviral properties of rimantadine and amantadine may be related to the interaction of these drugs with the cell membrane, which can affect virus penetration into the cell as well as maturation of the viral particle at the cell membrane.     

Enhancement of acetaldehyde-protein adduct formation by L-ascorbate

The effect of L-ascorbate on the binding of [14C]acetaldehyde to bovine serum albumin was examined. In the absence of ascorbate, acetaldehyde reacted with albumin to form both unstable (Schiff bases) and stable adducts. Ascorbate (5 mM) caused a time-dependent increase in the formation of total acetaldehyde-albumin adducts, which were comprised mainly of stable adducts. Significant enhancement of adduct formation by ascorbate was observed at acetaldehyde concentrations as low as 5 microM. An ascorbate concentration as low as 0.5 mM was still effective in stimulating stable adduct formation. The electron acceptor, 2,6 dichlorophenolindophenol, prevented the ascorbate-induced increase in albumin-adduct formation. Ascorbate also caused enhanced acetaldehyde adduct formation with other purified proteins, including cytochrome c and histones, as well as the polyamino acid, poly-L-lysine. These results indicate that ascorbate, acting as a reducing agent, can convert unstable acetaldehyde adducts to stable adducts, and can thereby increase and stabilize the binding of acetaldehyde to proteins.     

Some factors affecting phosphate transport in a perfused rat heart preparation.

Pi uptake by a perfused rat heart preparation did not require the presence of any other permeant anion, but was markedly dependent on the extracellular Na+ concentration and accelerated when tissue oxygenation was inadequate. Pi efflux was also independent of other permeant anions, but apparently varied with the intracellular Na+ concentration. Cardiac Pi efflux was not sensitive to a number of inhibitors that clock Cl- movement in heart and other tissues. Both uptake and efflux apparently proceed via a reversible electroneutral co-transport system linked to the transmembrane Na+ gradient. Pi uptake was independent of cardiac work load, but the efflux rate was sharply accelerated after an increase in aortic pressure development, with a slow return towards basal values during sustained periods of high work output. An inverted biphasic effect on the efflux rate was observed after a reduction in cardiac work load. Mild hypoxia and respiratory and metabolic acidosis each resulted in a transient acceleration of Pi efflux followed by a return towards basal values during prolonged exposure to the stimulus, whereas respiratory and metabolic alkalosis produced a similar but inverted response. The origin of these phasic effects on Pi efflux remains to be identified at present.     

Electrophoretic transport of Tl+ in mitochondria

Summary The distribution of Tl⁺ between rat liver mitochondria and the medium was studied; millimolar or smaller concentrations of Tl⁺ were labeled with²⁰⁴Tl. The Tl⁺ distribution responded to transient diffusion potentials in a way that indicated electrophoretic movements of Tl⁺. The diffusion potentials were induced by efflux of K⁺ in response to addition of valinomycin to nonrespiring mitochondria suspended in a medium with low concentrations of K⁺ or by efflux of H⁺ induced by making the medium more alkaline in the presence of a protonophorous (proton-conducting) uncoupling agent. Changes in membrane potential induced by valinomycin were followed with the aid of safranine. Tl⁺ brought about collapse of the diffusion potential. It is concluded that Tl⁺ is able to penetrate the mitochondrial membrane electrophoretically.