Biomedical subjects

D Bozovic

Publications and source records attributed to D Bozovic.

4 recordsLinked to original sources

PubMed2003

Spontaneous oscillation by hair bundles of the bullfrog's sacculus.

One prominent manifestation of mechanical activity in hair cells is spontaneous otoacoustic emission, the unprovoked emanation of sound by an internal ear. Because active hair bundle motility probably constitutes the active process of nonmammalian hair cells, we investigated the ability of hair bundles in the bullfrog's sacculus to produce oscillations that might underlie spontaneous otoacoustic emissions. When maintained in the normal ionic milieu of the ear, many bundles oscillated spontaneously through distances as great as 80 nm at frequencies of 5-50 Hz. Whole-cell recording disclosed that the positive phase of movement was associated with the opening of transduction channels. Gentamicin, which blocks transduction channels, reversibly arrested oscillation; drugs that affect the cAMP phosphorylation pathway and might influence the activity of myosin altered the rate of oscillation. Increasing the Ca 2+ concentration rendered oscillations faster and smaller until they were suppressed; lowering the Ca 2+ concentration moderately with chelators had the opposite effect. When a bundle was offset with a stimulus fiber, oscillations were transiently suppressed but gradually resumed. Loading a bundle by partial displacement clamping, which simulated the presence of the accessory structures to which a bundle is ordinarily attached, increased the frequency and diminished the magnitude of oscillation. These observations accord with a model in which oscillations arise from the interplay of the hair bundle's negative stiffness with the activity of adaptation motors and with Ca 2+-dependent relaxation of gating springs.

Animals↗

PubMed2003

Hair-bundle movements elicited by transepithelial electrical stimulation of hair cells in the sacculus of the bullfrog.

Electrically evoked otoacoustic emission is a manifestation of reverse transduction by the inner ear. We present evidence for a single-cell correlate of this phenomenon, hair-bundle movement driven by transepithelial electrical stimulation of the frog's sacculus. Responses could be observed at stimulus frequencies up to 1 kHz, an order of magnitude higher than the organ's natural range of sensitivity to acceleration or sound. Measurements at high-stimulus frequencies and pharmacological treatments allow us to distinguish two mechanisms that mediate the electrical responses: myosin-based adaptation and Ca(2+)-dependent reclosure of transduction channels. These mechanisms also participate in the active process that amplifies and tunes the mechanical responses of this receptor organ. Transient application of the channel blocker gentamicin demonstrated the crucial role of mechanoelectrical transduction channels in the rapid responses to electrical stimulation. A model for electrically driven bundle motion that incorporates the negative stiffness of the hair bundle as well as its two mechanisms of motility captures the essential features of the measured responses.

Acoustic Stimulation↗

PubMed2001

Fabry - Perot interference in a nanotube electron waveguide.

The behaviour of traditional electronic devices can be understood in terms of the classical diffusive motion of electrons. As the size of a device becomes comparable to the electron coherence length, however, quantum interference between electron waves becomes increasingly important, leading to dramatic changes in device properties. This classical-to-quantum transition in device behaviour suggests the possibility for nanometer-sized electronic elements that make use of quantum coherence. Molecular electronic devices are promising candidates for realizing such device elements because the electronic motion in molecules is inherently quantum mechanical and it can be modified by well defined chemistry. Here we describe an example of a coherent molecular electronic device whose behaviour is explicitly dependent on quantum interference between propagating electron waves-a Fabry-Perot electron resonator based on individual single-walled carbon nanotubes with near-perfect ohmic contacts to electrodes. In these devices, the nanotubes act as coherent electron waveguides, with the resonant cavity formed between the two nanotube-electrode interfaces. We use a theoretical model based on the multichannel Landauer-Büttiker formalism to analyse the device characteristics and find that coupling between the two propagating modes of the nanotubes caused by electron scattering at the nanotube-electrode interfaces is important.

Electronics↗

PubMed2001

Resonant electron scattering by defects in single-walled carbon nanotubes.

We report the characterization of defects in individual metallic single-walled carbon nanotubes by transport measurements and scanned gate microscopy. A sizable fraction of metallic nanotubes grown by chemical vapor deposition exhibits strongly gate voltage-dependent resistance at room temperature. Scanned gate measurements reveal that this behavior originates from resonant electron scattering by defects in the nanotube as the Fermi level is varied by the gate voltage. The reflection coefficient at the peak of a scattering resonance was determined to be about 0.5 at room temperature. An intratube quantum dot device formed by two defects is demonstrated by low-temperature transport measurements.

Carbon↗