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D P Corey

Publications and source records attributed to D P Corey.

64 records · Page 4Linked to original sources
PubMed1987

Adaptation of mechanoelectrical transduction in hair cells of the bullfrog's sacculus.

Adaptation in a vestibular organ, the bullfrog's sacculus, was studied in vivo and in vitro. In the in vivo experiments, the discharge of primary saccular neurons and the extracellular response of saccular hair cells were recorded during steps of linear acceleration. The saccular neurons responded at the onset of the acceleration steps, then adapted fully within 10-50 msec. The extracellular (microphonic) response of the hair cells adapted with a similar time course, indicating that the primary sources of the neural adaptation are peripheral to the afferent synapse--in the hair cell, its mechanical inputs, or both. Evidence for hair cell adaptation was provided by 2 in vitro preparations: after excising the sacculus and removing the accessory structures, we recorded either the extracellular hair cell response to displacement of the otolithic membrane or the intracellular hair cell response to hair bundle displacement. In both cases the response to a step stimulus adapted. The adaptation involved a shift in the displacement-response curve along the displacement axis, so that the cell's operating point was reset toward the static position of its hair bundle. This displacement shift occurred in response to both depolarizing and hyperpolarizing stimuli. Its time course varied among cells, from tens to hundreds of milliseconds, and also varied with the concentration of Ca2+ bathing the apical surfaces of the hair cells. Voltage-clamp experiments suggested that the displacement shift does not depend simply on ion entry through the hair cell's transduction channels and can occur at a fixed membrane potential. The possible role of the displacement-shift process in the function of the frog's sacculus as a very sensitive vibration detector is discussed.

Animals↗
PubMed1984

The calcium current in inner segments of rods from the salamander (Ambystoma tigrinum) retina.

Solitary rod inner segments were isolated from salamander retinae. Their Ca current was studied with the 'whole-cell, gigaseal' technique (Hamill, Marty, Neher, Sakmann & Sigworth, 1981). The soluble constituents of the cytoplasm exchanged with the solution in the pipette. The external solution could be changed during continuous perfusion. Membrane voltage was controlled with a voltage clamp. After permeant ions other than Ca were replaced with impermeant ions (i.e. tetraethylammonium as a cation, and aspartate or methanesulphonate as an anion), an inward current remained. It activated at approximately -40 mV, reached a maximum at approximately 0 mV, and decreased as the membrane was further depolarized. The size of the current increased when Ba was substituted for external Ca. The current was blocked when Ca was replaced with Co. The voltage at which the current was half-maximum shifted from approximately -22 to -31 mV during the initial 3 min of an experiment. The maximum amplitude of the current continuously declined during the entire course of an experiment. The time course for activation of the Ca current following a step of depolarization could be described by the sum of two exponentials. The time constant of the slower exponential was voltage dependent. Deactivation following repolarization could also be described by the sum of two exponentials. Both time constants for deactivation were independent of voltage (between -30 and 0 mV) and faster than the slower time constant for activation. When the internal Ca concentration was buffered by 10 mM-EGTA, the Ca current did not inactivate during several seconds of maintained depolarization. When the concentration of EGTA was reduced to 0.1 mM, the Ca current declined and the membrane conductance decreased during several seconds of maintained depolarization. This inactivation was incomplete and only occurred after a substantial quantity of Ca entered. Following repolarization the Ca conductance recovered from inactivation. In contrast, the continuous decline observed during the course of an experiment (item 3) was not reversible. The difference suggests that inactivation and the decline are distinct processes.

Ambystoma↗
PubMed1983

Analysis of the microphonic potential of the bullfrog's sacculus.

The sensory epithelium from the bullfrog's sacculus was mounted between two chambers and stimulated by moving the otolithic membrane with a piezoelectric stimulator. The evoked response was measured as the transepithelial "microphonic" potential or, when the epithelium was voltage clamped, as the microphonic current. Microphonic responses were similar to those recorded in other preparations: the whole organ produced a "2f" response (i.e., a response of a frequency twice that of the stimulus) which could be changed to a single-polarity response by stimulating cells of a single polarity; the response saturated asymmetrically with displacement, producing a rectification; and the amplitude declined at high and low frequencies. To determine the cellular elements responsible for generation of the microphonic potential, the equivalent circuit of the epithelium was estimated from morphological and electrophysiological data, and responses to step displacement stimuli were recorded. Four elements in particular shape the microphonic potential: the complex impedance of the extracellular current path, the saturating displacement-conductance curve, an adaptation mechanism which shifts that curve, and a voltage-dependent K+ conductance in the basolateral hair cell membrane. A quantitative model incorporating these elements accurately reproduces the observed responses.

Acoustic Stimulation↗
PubMed1983

Kinetics of the receptor current in bullfrog saccular hair cells.

The receptor current of hair cells from the bullfrog's sacculus was measured by voltage clamp recording across the isolated sensory epithelium. Several hundred hair cells were stimulated en masse by moving the overlying otolithic membrane with a piezoelectrically activated probe. As measured by optical recording of otolithic membrane motion, the step displacement stimuli reached their final amplitudes of up to 1 micrometer within 100 microseconds. The relationship between displacement and steady-state receptor current is an asymmetric, sigmoidal curve about 0.5 micrometer in extent. The time constant of the approach to steady state depends upon the magnitude of the hair bundle displacement and ranges from 100 to 500 microseconds at 4 degrees C; the time course is faster with larger displacements or at higher temperatures. Both the displacement-response curve and the kinetics of the response are changed by alterations in the Ca2+ concentration at the apical surface of the cells. The characteristics of the response are not consistent with simple models for the transduction process that involve enzymatic regulation of channel proteins or diffusible second messengers. Mechanical stimulation is instead posited to act directly by altering the free energy difference between the open and closed forms of the transduction channel, thereby inducing a redistribution between these states. The dependences of the response kinetics on displacement and on temperature suggest that the thermal interconversion between open and closed transduction channels is limited by an enthalpy of activation of about 12 kcal/mol.

Acoustic Stimulation↗
PubMed1980

Mechanical stimulation and micromanipulation with piezoelectric bimorph elements.

Piezoelectric bimorph elements are versatile and inexpensive electromechanical transducers which may be used to construct fast mechanical stimulators and finely controlled micromanipulators. The mechanical stimulators described provide continuously graded displacements ranging from nanometers to about a millimeter, or forces equivalent to 0-7 g. Appropriately designed units can produce small step displacements complete within 100 microseconds. Micromanipulators are described which generate 3-dimensional motion under remote electrical control and which enable positioning within a few tenths of a micrometer. They are sufficiently stable to hold glass microelectrodes for cell penetration or probes for microdissection. The two significant drawbacks of bimorph elements are mechanical resonance and continued movement following displacement, or 'creep", but methods have been developed to compensate for these. A number of methods are available to measure motion of bimorphs with spatial resolution of 10 nm and temporal resolution of 2 microseconds in favorable situations.

Animals↗
PubMed1979

Response latency of vertebrate hair cells.

An in vitro preparation of hair cells from the bullfrog sacculus produces a transepithelial microphonic potential in response to well-defined mechanical stimuli. If corrected for the electrical time constant of the epithelium, the response follows a fast stimulus with a 40-microsecond delay at 22 degree C. The short latency and its modest temperature dependence limit possible models for transduction by hair cells.

Animals↗
PubMed1978

Controlled bending of high-resistance glass microelectrodes.

The short working distance of compound microscope lenses in many cases prevents microelectrode penetrations of cells perpendicular to the cell surface. Bending electrodes very near their tips removes this constraint. A method is described for bending glass microelectrodes with a hot filament while their tips are immersed in a water drop. Immersion protects the fine electrode tips from the heat and provides control over the angle through which the electrodes are bent.

Electrophysiology↗
PubMed1977

Sensitivity, polarity, and conductance change in the response of vertebrate hair cells to controlled mechanical stimuli.

Hair cells, the primary receptors of the auditory, vestibular, and lateral-line sensory systems, produce electrical signals in response to mechanical stimulation of their apical hair bundles. We employed an in vitro preparation and intracellular recording to investigate the transduction mechanism of hair cells in the sacculus from the inner ear of the bullfrog (Rana catesbeiana). When stimulated directly by mechanical deflection of their hair bundles, these cells gave graded responses up to 15 mV in amplitude; the peak sensitivity was about 20 mV/micron deflection. The depolarizing component of the receptor potential corresponding to stimuli directed towards the kinocilium. Depolarizing responses were associated with a membrane resistance decrease, and hyperpolarizing responses with a resistance increase. Action potentials, possibly calcium spikes, were occasionally evoked in hair cells by mechanical or electrical stimulation.

Animals↗