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Biomedical subjects

A Hermann

Publications and source records attributed to A Hermann.

125 records · Page 7Linked to original sources
PubMed1981

Caffeine blocks the delayed K+ outward current of molluscan neurons.

Extracellular application of caffeine inhibits the delayed K+ outward current of Aplysia neurons in a dose dependent manner without changing the kinetics. Half-maximum blockade is produced with a concentration of 16.0 +/- 0.7 mM (S.E.M.) caffeine after 1-2 min. Intracellular injection of caffeine has an almost immediate blocking effect. The evidence suggests that the blocking site is at or close to the inner surface of the cellular membrane.

Animals↗
PubMed1981

Effects of 4-aminopyridine on potassium currents in a molluscan neuron.

The effects of 4-aminopyridine (4-AP) on the delayed K+ current and on the Ca2+-activated K+ current of the Aplysia pacemaker neurons R-15 and L-6 were studied. The delayed outward K+ current was measured in Ca2+-free artificial seawater (ASW) containing tetrodotoxin (TTX), using brief depolarizing clamp pulses. External (and internal) 4-AP blocks the delayed K+ current in a dose-dependent manner but does not block the leakage current. Our results show that one 4-AP molecule combines with a single receptor site and that the block is voltage dependent with an apparent dissociation constant (K4-AP) of approximately 0.8 mM at 0 mV. K4-AP increases e-fold for a 32-mV change in potential, which is consistent with the block occurring approximately 0.8 of the distance through the membrane electrical field. The 4-AP block appears to depend upon stimulus frequency as well as upon voltage. The greater speed of onset of the block produced by internal 4-AP relative to when it is used externally suggests that 4-AP acts from inside the cell. The Ca2+-activated K+ current was measured in Ca2+-free ASW containing TTX, using internal Ca2+-ion injection to directly activate the K+ conductance. Low external 4-AP concentrations (less than 2 mM) have no effect on the Ca2+-activated K+ current, but concentrations of 5 mM or greater increase the K+ current. Internal 4-AP has the same effect. The opposing effects of 4-AP on the two components of the K+ current can be seen in measurements of the total outward K+ current at different membrane potentials in normal ASW and during the repolarizing phase of the action potential.

4-Aminopyridine↗
PubMed1981

Effects of tetraethylammonium on potassium currents in a molluscan neurons.

The effects of tetraethylammonium (TEA) on the delayed K+ current and on the Ca2+-activated K+ current of the Aplysia pacemaker neurons R-15 and L-6 were studied. The delayed outward K+ current was measured in Ca2+-free ASW containing tetrodotoxin (TTX), using brief depolarizing clamp pulses. External TEA blocks the delayed K+ current reversibly in a dose-dependent manner. The experimental results are well fitted with a Michaelis-Menten expression, assuming a one-to-one reaction between TEA and a receptor site, with an apparent dissociation constant of 6.0 mM. The block depends on membrane voltage and is reduced at positive membrane potentials. The Ca2+-activated K+ current was measured in Ca2+-free artificial seawater (ASW) containing TTX, using internal Ca2+ ion injection to directly activate the K+ conductance. External TEA and a number of other quaternary ammonium ions block the Ca2+-activated K+ current reversibly in a dose-dependent manner. TEA is the most effective blocker, with an apparent dissociation constant, for a one-to-one reaction with a receptor site, of 0.4 mM. The block decreases with depolarization. The Ca2+-activated K+ current was also measured after intracellular iontophoretic TEA injection. Internal TEA blocks the Ca2+-activated K+ current (but the block is only apparent at positive membrane potentials), is increased by depolarization, and is irreversible. The effects of external and internal TEA can be seen in measurements of the total outward K+ current at different membrane potentials in normal ASW.

Animals↗
PubMed1981

Intracellular calcium and the control of neuronal pacemaker activity.

Pacemaker activity of the Aplysia bursting pacemaker neuron R-15 was analyzed. It was shown that the free intracellular Ca2+ concentration, as measured by arsenazo III, increases during the depolarizing phase of the pacemaker cycle and declines throughout the hyperpolarizing phase that follows. This increase in Ca2+ results from the activation of voltage-dependent Ca2+ channels that open during the depolarizing phase of the cycle. The extracellular K+ concentration also increases during the depolarizing phase of the cycle and is correlated with an outward K+ current that opposes the inward current carried by Ca2+ ions. The increase in internal Ca2+ is sufficient to activate a K+ conductance that depends on the magnitude of the change in internal Ca2+ and on membrane potential, which is responsible for the hyperpolarizing phase of the cycle. It is proposed that the membrane oscillation depends on three separate but linked systems, which include a voltage-dependent Ca2+ channel, the internal Ca2+ concentration, and a Ca2+-activated K+ channel.

Action Potentials↗
PubMed1979

External and internal effects of tetraethylammonium on voltage-dependent and Ca-dependent K+ currents components in molluscan pacemaker neurons.

Ca-dependent and voltage-dependent K+ currents in Aplysia pacemaker neurons were studied separately by electrophoretic injections of Ca2+ ions into the cells to induce the Ca-dependent component and by step depolarizations in the absence of external Ca2+ ions to induce the voltage-dependent component. Intracellular tetraethylammonium (TEA) blocks the voltage-dependent but not the Ca-dependent K+ current. Extracellular TEA blocks both components reversibly but is more effective in inhibiting the Ca-dependent K+ currents. Our results suggest that there are TEA receptor sites for the voltage-dependent K+ current on each side of the membrane, but only an external receptor site for the Ca-dependent K+ current.

Animals↗
PubMed1979

Internal effects of divalent cations on potassium permeability in molluscan neurones.

1. Electrophoretic injection of Ca ions into Aplysia pace-maker neurones activates an outward current, carried primarily by K ions, whose magnitude is determined by the intensity and duration of the injection current, the position of the injection electrode within the cell and the holding potential. 2. The efflux of K ions measured with an extracellular K sensitive electrode is a linear function of the Ca activated outward current and disappears at its reversal potential. 3. The outward current decays exponentially with an early and late phase. The early but not the late phase is temperature dependent with a Q10 of about 3-5. 4. Of the divalent cations which activate the outward current, Ca is the most effective followed by Cd, Hg, Sr, Mn and Fe. Injections of Ba, Co, Cu, Mg, Ni and Zn are ineffective. 5. Low temperatures or prolonged injection of Cd or Hg, increase the amplitude of the outward current activated by Ca. 6. Prolonged injection of Ba inhibits the Ca activated outward current and reduces substantially all currents carried by K ions. 7. It is concluded that the effectiveness of a divalent cation in activating the K current is, in part, related to its ionic radius, and that the site of activation can accommodate ionic radii between about 0.76 and 1.13 A.

Animals↗
PubMed1977

[Susceptibility to Thiamphenicol and Chloramphenicol of Anaerobic Bacteria (author's transl)].

The in vitro susceptibility to thiamphenicol and chloramphenicol of 272 anaerobes, most of which were recent clinical isolated, was determined by broth dilution tests, With chloramphenicol, 133 anaerobic gram-negative non-sporing rods (48 Bacteroides fragilis, 13 B. thetaiotaomicron, 14 B. oralis, 16 Sphaerophorus varius etc.) had MIC values of 0.03 through 16 microng/ml. Very similar results (MIC, 0.06-16 microng/ml) were obtained with thiamphenicol. In concentrations of 4 microng/ml or less chloramphenicol inhibited 90.2% and thiamphenicol 78.95% of the strains. Strains with only moderate sensitivity to both antibiotics (MIC, 8 or 16 microng/ml) belonged to B. fragilis or other Bacteroides species. Members of the Fusobacterium and Sphaerophorus group were susceptible to less than or equal to 2 microng chloramphenicol/ml and less than or equal to 4 microng thiamphenicol/ml respectively. With both antibiotics, 102 strains of gram-positive non-sporing anaerobes (P. acnes, Peptostreptococcus spp., Peptococcus spp.) were susceptible to less than or equal to 8 microng/ml. Of 37 Clostridium isolates, 35 (belonging to C. perfringens, C. septicum, C. cadaveris etc.) were inhibited by concentrations of 8 microng/ml or less of chloramphenicol and thiamphenicol. Only one strain each of C. perfringens and Clostridium sp. had an MIC of 16 microng thiamphenicol/ml. Accordingly, resistance to thiamphenicol or chloramphenicol was not observed. A standardized monodisk agardiffusion test was performed on 40 Bacteroidaceae, 18 Peptococcaceae and 20 C, (P.) acnes strains. Only a poor correlation was observed between MIC and zone size for thiamphenicol and chloramphenicol. Therefore, inhibition zone diameter measurement cannot be regarded as a reliable method to detect chloramphenicol or thiamphenicol resistance in anaerobes. Thiamphenicol, which is virtually as active against anaerobes as chloramphenicol but lacks serious toxicity, may well play an important role in the therapy of various anaerobic infections.

Anti-Bacterial Agents↗
PubMedDate not supplied

Spatial and dye correlation analysis of intracellular Ca2+ distribution.

Intracellular Ca2+ is an important regulator of many cellular processes. Besides ion channels and transporters in the plasmalemma, changes in [Ca]i can be mediated by uptake and release mechanisms of internal organelles. Theoretical and experimental procedures are developed aiming to reveal the distribution of internal Ca2+ pools and their role in generating complicated spatial patterns of [Ca]i gradients. Cultured pyramidal neurons from rat hippocampus were loaded with Ca(2+)-sensitive fluorescent dyes, fura-2 and fluo-3. Cell images were partitioned according to pixel amplitude and highlighted pictures were characterized by their intensity, relative area and connectivity. This approach facilitates the localization of the sites of Ca2+ release from internal stores induced by application of different agents. After each trial, neurons were stained with dyes, acridine orange or DiOC6, which bind preferentially to nucleus and endoplasmic reticulum. A correlation between images confirmed the spatial localization of Ca2+ release sites. Application of the partition procedure also gave a clear evidence for the importance of Ca2+ influx in the mechanism of [Ca]i oscillations.

Aniline Compounds↗
PubMedDate not supplied

Hypotonicity and ethanol modulate BK channel activity and chloride currents in GH4/C1 pituitary tumour cells.

AIM: Description of the effects of hypotonic cell swelling and ethanol on maxi Ca2+-activated K+ channel (BK channel) activity and Cl- channel activity in GH4/C1 pituitary tumour cells. METHODS: Whole cell-, cell attached- and outside-out patch clamp measurements, fluorescence (fluo-3) measurements of intracellular Ca2+ concentration, cell size video monitoring. RESULTS: GH4/C1 pituitary tumour cells respond to both hypotonicity and ethanol with cell swelling which is followed by a regulatory volume decrease (RVD). Tetraethylammonium and 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS) induced cell swelling per se and inhibited hypotonicity induced RVD. Ethanol-induced swelling is paralleled by an increase in the intracellular Ca2+ concentration and augmented by DIDS. BK channel activation by hypotonicity and ethanol is demonstrated in patch clamp experiments both in intact cells (cell attached configuration) and a subset of excised membrane patches (outside-out configuration). Cell swelling and addition of ionomycin under isotonic conditions leads to the activation of outwardly rectifying Cl- currents with time dependent activation at positive potentials. CONCLUSIONS: In GH4/C1 cells both hypotonicity and ethanol lead to cell swelling, RVD and to activation of BK channels. The hypotonicity-induced BK channel activation can also be observed in cell free outside-out patches. Hypotonicity, but not ethanol leads to the activation of Cl- channels with features of Ca2+-activated Cl- currents.

3T3 Cells↗
PubMedDate not supplied

[The significance of zonography in X-ray diagnosis of midfacial fractures].

The possibilities offered by panoramic zonography (MT program) in the diagnosis of the midface are outlined. The imaging quality of various anatomical structures is demonstrated both on the anatomical model and in clinical use. The benefits and limitations of this procedure are discussed. Zonography is a reliable instrument adding to the range of basic diagnostic procedures in the midfacial region.

Facial Bones↗