Biomaterial Database

Variation of membrane properties in hair cells isolated from the turtle cochlea. 1987

J J Art, and R Fettiplace

Physiological Laboratory, University of Cambridge.

1. Hair cells were enzymatically isolated from identified regions of the turtle basilar papilla and studied with the patch-electrode technique. The experimental aim was to relate the resonance properties seen during current injection to the membrane currents measured in the same cell under whole-cell voltage clamp. 2. Solitary hair cells had resting potentials of about -50 mV, and produced a damped oscillation in membrane potential at the onset and termination of a small current step; the resonant frequency varied from 9 to 350 Hz between cells, and was correlated with the region of papilla from which a cell had been isolated. The inferred frequency map was consistent with the tonotopic arrangement described previously in the intact papilla. 3. Depolarizations from the resting potential under voltage clamp activated a large net outward current with a steep voltage dependence, and the steady-state current-voltage relationship was strongly rectified about the resting potential. Input resistances tended to be smaller in cells with higher resonant frequencies, although there was no concurrent variation in membrane area as inferred from the cell capacitance. 4. The kinetics of the outward current evoked by a small depolarizing step depended upon the resonant frequency, fo, of the hair cell, and were slower in low-frequency cells. On repolarization to the resting potential the current decayed exponentially with a time constant that changed from 150 ms in the lowest-frequency cell to less than 1 ms in the highest-frequency one. The time constant was approximately proportional to 1/f0(2). 5. Following repolarization to different membrane potentials, the tail current was found to reverse around -80 mV, indicating that the outward current was due mainly to K+. 6. The outward current was abolished by extracellular application of 25 mM-tetraethylammonium chloride (TEA), or on exchange of Cs+ for K+ in the intracellular medium filling the recording electrode, each experiment supporting the contention that K+ is the major current carrier. Such treatments also removed the oscillations in membrane potential evoked by imposed current steps. 7. Addition of TEA or intracellular perfusion with Cs+ also revealed a fast inward current with an ionic sensitivity consistent with its being carried by Ca2+. Like the K+ current, the Ca2+ current was activated by small depolarization from the resting potential, and over this voltage range it was about five to ten times smaller than the K+ current. Its activation was more rapid than the fastest outward currents in high-frequency cells.(ABSTRACT TRUNCATED AT 400 WORDS)

UI	MeSH Term	Description	Entries
D007473	Ion Channels	Gated, ion-selective glycoproteins that traverse membranes. The stimulus for ION CHANNEL GATING can be due to a variety of stimuli such as LIGANDS, a TRANSMEMBRANE POTENTIAL DIFFERENCE, mechanical deformation or through INTRACELLULAR SIGNALING PEPTIDES AND PROTEINS.	Membrane Channels,Ion Channel,Ionic Channel,Ionic Channels,Membrane Channel,Channel, Ion,Channel, Ionic,Channel, Membrane,Channels, Ion,Channels, Ionic,Channels, Membrane
D007700	Kinetics	The rate dynamics in chemical or physical systems.
D008564	Membrane Potentials	The voltage differences across a membrane. For cellular membranes they are computed by subtracting the voltage measured outside the membrane from the voltage measured inside the membrane. They result from differences of inside versus outside concentration of potassium, sodium, chloride, and other ions across cells' or ORGANELLES membranes. For excitable cells, the resting membrane potentials range between -30 and -100 millivolts. Physical, chemical, or electrical stimuli can make a membrane potential more negative (hyperpolarization), or less negative (depolarization).	Resting Potentials,Transmembrane Potentials,Delta Psi,Resting Membrane Potential,Transmembrane Electrical Potential Difference,Transmembrane Potential Difference,Difference, Transmembrane Potential,Differences, Transmembrane Potential,Membrane Potential,Membrane Potential, Resting,Membrane Potentials, Resting,Potential Difference, Transmembrane,Potential Differences, Transmembrane,Potential, Membrane,Potential, Resting,Potential, Transmembrane,Potentials, Membrane,Potentials, Resting,Potentials, Transmembrane,Resting Membrane Potentials,Resting Potential,Transmembrane Potential,Transmembrane Potential Differences
D011188	Potassium	An element in the alkali group of metals with an atomic symbol K, atomic number 19, and atomic weight 39.10. It is the chief cation in the intracellular fluid of muscle and other cells. Potassium ion is a strong electrolyte that plays a significant role in the regulation of fluid volume and maintenance of the WATER-ELECTROLYTE BALANCE.
D002118	Calcium	A basic element found in nearly all tissues. It is a member of the alkaline earth family of metals with the atomic symbol Ca, atomic number 20, and atomic weight 40. Calcium is the most abundant mineral in the body and combines with phosphorus to form calcium phosphate in the bones and teeth. It is essential for the normal functioning of nerves and muscles and plays a role in blood coagulation (as factor IV) and in many enzymatic processes.	Coagulation Factor IV,Factor IV,Blood Coagulation Factor IV,Calcium-40,Calcium 40,Factor IV, Coagulation
D003051	Cochlea	The part of the inner ear (LABYRINTH) that is concerned with hearing. It forms the anterior part of the labyrinth, as a snail-like structure that is situated almost horizontally anterior to the VESTIBULAR LABYRINTH.	Cochleas
D006198	Hair Cells, Auditory	Sensory cells in the organ of Corti, characterized by their apical stereocilia (hair-like projections). The inner and outer hair cells, as defined by their proximity to the core of spongy bone (the modiolus), change morphologically along the COCHLEA. Towards the cochlear apex, the length of hair cell bodies and their apical STEREOCILIA increase, allowing differential responses to various frequencies of sound.	Auditory Hair Cells,Cochlear Hair Cells,Auditory Hair Cell,Cell, Cochlear Hair,Cells, Cochlear Hair,Cochlear Hair Cell,Hair Cell, Auditory,Hair Cell, Cochlear,Hair Cells, Cochlear
D000200	Action Potentials	Abrupt changes in the membrane potential that sweep along the CELL MEMBRANE of excitable cells in response to excitation stimuli.	Spike Potentials,Nerve Impulses,Action Potential,Impulse, Nerve,Impulses, Nerve,Nerve Impulse,Potential, Action,Potential, Spike,Potentials, Action,Potentials, Spike,Spike Potential
D000818	Animals	Unicellular or multicellular, heterotrophic organisms, that have sensation and the power of voluntary movement. Under the older five kingdom paradigm, Animalia was one of the kingdoms. Under the modern three domain model, Animalia represents one of the many groups in the domain EUKARYOTA.	Animal,Metazoa,Animalia
D001464	Barium	An element of the alkaline earth group of metals. It has an atomic symbol Ba, atomic number 56, and atomic weight 138. All of its acid-soluble salts are poisonous.