Biomedical subjects

I Ivens

Publications and source records attributed to I Ivens.

5 recordsLinked to original sources

PubMed1986

Inhibition of a voltage-dependent Ca current by concanavalin A.

Incubation of the hypotrichous ciliate Stylonychia mytilus in fluorescein-labeled concanavalin A (Con A, 0.1-0.5 microgram/ml) produced a strong fluorescence of its membranelles, but comparatively weak fluorescence of the other compound cilia and of the somatic membrane. Compared to untreated cells, the frequency of spontaneous backward movements was reduced in the presence of 0.5 microgram/ml ConA. In electrophysiological experiments Con A altered the excitability of the cell membrane. The two-peak action potential lost its second component which is associated with voltage-dependent Ca channels in the membranelles. The corresponding Ca current (Ca current I) was inhibited by low concentrations of Con A (0.2-0.5 microgram/ml). A second voltage-dependent Ca current (Ca current II) was not affected. Reducing the K outward current by intracellular Cs and/or extracellular tetraethylammonium, or changing the holding potential, did not restore the Con A-sensitive Ca current I. Con A also inhibited this current when Ca was replaced by Ba. The inhibitory effect of Con A on the voltage-dependent Ca current I was prevented by 10-30 mM alpha-methyl-D-mannoside, and the lectin wheat germ agglutinin (20 micrograms/ml) did not affect the Ca currents, indicating that the Con A effect was mediated by binding to specific sugar residues on the excitable membrane. The succinylated dimeric derivative of Con A did not inhibit Ca current I up to concentrations of 5 micrograms/ml. It is concluded that the two voltage-dependent Ca currents in Stylonychia can be chemically isolated due to their different sensitivity to Con A, which appears to bind preferentially to sites near or at the Ca channel in the membranellar membrane.

Animals↗

PubMed1986

Changes in voltage-dependent calcium currents during the cell cycle of the ciliate Stylonychia.

Electrophysiological properties of the hypotrichous ciliate Stylonychia mytilus were studied at two stages of its cell cycle: within 30 min after cell division and several hours thereafter. The action potential wave form, and the relative amount of two voltage-dependent calcium inward currents are significantly different in 'young' daughter cells as compared with 'adult' cells. The ratio between total inward and outward current is also larger in 'young' cells. The results provide evidence that during its cell cycle Stylonychia undergoes qualitative developmental changes with respect to its ionic channels in the membrane. These changes may explain the different cell behaviour observed up to 1 h after cell division.

Action Potentials↗

PubMed1986

Different properties of two voltage-dependent inward currents of the ciliate Stylonychia mytilus.

1. Membrane currents and membrane potentials of the fresh-water ciliate Stylonychia mytilus were investigated by voltage-clamp and constant-current injection techniques. 2. The Ca-dependent action potential of Stylonychia in a solution containing 0.1 mM-CaCl2 was prolonged by the addition of Mg or Na ions. 3. In a nominally Ca-free solution, containing 2 mM-MgCl2, the cells generated repetitive, spontaneous action potentials of relatively small amplitude (17 mV). The addition of 0.5 microgram concanavalin A/ml completely inhibited these action potentials in 2 mM-Mg. 4. In voltage-clamp experiments in standard solution, the inward current-voltage relationship has two maxima, confirming the existence of two different voltage-dependent Ca currents in Stylonychia: inward current I and II. In a nominally Ca-free, Mg-containing solution, the remaining inward current was inhibited by concanavalin A, a specific inhibitor of inward current I. No residual second inward current (current II) was detected in a solution containing Mg and concanavalin A. 5. Experiments, with altered ratio of Ca and Mg ions and constant concentration of divalent cations (mole-fraction experiments), showed that Mg and Ca do not inhibit each other's passage through channel I. Calculations assuming a Ca-channel model with one cation-binding site per ion channel I showed good correlation with the experimental data. 6. A similar inward current was seen after replacement of Mg by Na in nominally Ca-free solution.

Action Potentials↗

PubMed1982

Apparent delay between light-induced receptor current and receptor potential in the Limulus ventral nerve photoreceptor.

We measured receptor potential (ReP) and receptor current (ReC) under voltage-clamp conditions alternatingly evoked by successive identical 10 ms light flashes in the ventral nerve photoreceptor of Limulus. At high stimulus intensities the apparent latency of the ReP is 4-15 ms shorter than that of the ReC. At lower light intensities the difference is even larger. High amplification reveals that the light response starts with two phases corresponding to two current components. The initial first current component rises linearly, is much smaller than the second one and therefore is not detected with standard amplification. This first component, which is more pronounced at low light stimulus intensities, is caused either by a displacement or by a weak ionic current.

Animals↗

PubMedDate not supplied

Neurotoxicity testing during long-term studies.

Several tests and methods for the investigation of neurotoxicity were performed with female Wistar rats for up to 187 days. The methods were validated by testing 10 rats treated with beta,beta'-iminodipropionitrile (IDPN) and 10 control rats. Cage side observation of the animals revealed signs of altered behavior and motor dysfunction of the IDPN-treated rats. Results of a neuromuscular screen indicated changes in gait, righting reflex, grip strength and performance of the negative geotropism test. Investigation of the animals in activity monitors and on the accelerating rotarod showed changes of several parameters. The motor nerve conduction velocity, measured 6 months after the first treatment, was reduced by 6.7 meters per second in the IDPN group compared to controls. From the results of the tests it can be concluded that the methods chosen can be used during long-term studies but may be most useful for animals not older than 12 months.

Animals↗