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B Michaelis

Publications and source records attributed to B Michaelis.

7 recordsLinked to original sources
PubMed1989

HIV replication can be blocked by recombinant human interferon beta.

Recombinant human interferon beta (rIFN-beta) reduces replication of HIV in cultured peripheral mononuclear cells. The effect is most pronounced when high levels of the drug are employed. Maintenance of the rIFN-beta in culture is required since removal of the agent generally leads to a return of virus production by the infected cells. Moreover, at low concentrations of the drug, a breakthrough in HIV replication is observed. High concentrations of the rIFN-beta (greater than 100 units/ml) were cytotoxic for transformed T cells. This latter observations suggests that rIFN-beta might be useful in human T-cell malignancies. Beta interferon therefore might be useful for the treatment of HIV infection, particularly since side effects of the drug are limited in treated individuals.

Acquired Immunodeficiency Syndrome↗
PubMed1978

[Frequency domain analysis of the dynamic properties of the encoder in the slowly adapting crayfish stretch receptor neuron].

The transfer properties of the slowly adapting stretch receptor neuron can be suitably described in the frequency domain. The measurements are carried out by means of sinusoidally varying intracellular currents. The frequency response at low stimulation frequencies has been calculated from responses to current steps. At very low input frequencies the amplitude-frequency characteristic in the Bode diagram is nearly parallel to the abscissa. With increasing stimulation frequency the gain becomes larger and has a maximum at 1--3 Hz (stimulation frequency/carrier frequency (f/fo approximately 0.2). The amplitude-frequency characteristic decreases then, at first slowly then more rapidly, and reaches in the range of carrier frequency (f/fo approximately 1) small values. The phase-frequency characteristic shows at low input frequencies a small positive magnitude of 8--10(0). With higher stimulation frequencies the phase angle decreases and reaches negative values. In the range of carrier frequency the phase shift runs to -180 degrees. The present findings demonstrate also that the transfer function of the encoder depends on the carrier frequency of the receptor neuron. Larger carrier frequencies cause a decrease of the gain but the peak remains. This maximum shifts with increasing fo in direction to higher stimulation frequencies. The elimination of the encoder adaptation by means of a suitable model results in the frequency response of the real encoder. The above statements hold for higher stimulation frequencies too, but the typical differential behaviour at low frequencies disappears.

Animals↗
PubMed1975

Ion conductance changes associated with spike adaptation in the rapidly adapting stretch receptor of the crayfish.

The time course of the repetitive impulse discharges has been investigated for two high intensities of maintained depolarizing currents, 30 nA and 50 nA, for which the receptor adaptation was complete within 70 msec. The changes in sodium and potassium conductance associated with the decline in spike activity have been analyzed at different instances of time by interrupting in successive experiments the various action potentials in the pulse trains either at the early phase by holding the potential at about -60 mV and recording the inward current (upstroke-gNa) or by evaluating the delayed outward current flowing as the result of a depolarizing voltage pulse which at the end of the action potential re-increased the membrane potential by mV (after potentialgK). At the higher current intensity of 50 nA the discharge frequency was increased, while larger reductions in upstroke-gNa and after potential-gK during receptor adaptation became apparent. The progressive decrease in pulse amplitude from 99 mV to 63 or 55 mV is paralleled by a gradual reduction in upstroke-gNa from 97 mmho/cm-2 to 37 or 27.5 mmho/cm-2 and in after potential-gK from 11.5 mmho/cm-2 to about 7 mmho/cm-2. When under a stimulus of 30 nA the sodium conductance decreases to an average value of 37 mmho/cm-2 only a distorted spike can be elicited, while the spike activity was completely suppressed at upstroke-gNa equals 27.5 mmho/cm-2 was essentially the same under both conditions. The results have been interpreted in terms of the model for impulse generation formulated by Michaelis and Chaplain (1973). According to the model both sodium and potassium inactivation reduce the pulse amplitude. However, while Na-inactivation reduces the frequency of impulse discharge, the K-inactivation actually leads to an increase in spike frequency. As the frequency of the short train of pulses recorded under high-intensity current stimulation remained essentially unaltered, it is suggested that the coupling between Na- and K-inactivation actually leads to an increase in spike frequency. As the frequency of the short train of pulses recorded under high-intensity current stimulation remained essentially unaltered, it is suggested that the coupling between Na- and K-inactivation ensures a constancy of the information-carrying parameter, i.e. the average impulse density.

Action Potentials↗
PubMed1975

[Modelling of biological encoding mechanisms as a system with distributed parameters].

The encoder region in receptors and neurons is represented by the inhomogeneous origin of the axon. The axon diameter and the excitability are in fact space-dependent. For the analysis the soma is described by a system with concentrated parameters followed by an inhomogeneous axon. The membrane properties are approximated by the slightly modified Hodgkin-Huxley equations. The assumption that the space-dependence of the excitability originates in variations of the conductance value for sodium ions accounts for a number of experimental results. The influence of other membrane parameters upon the mechanism of impulse generation and transmission has also been analysed.

Axons↗