Biomaterial Database

Ca selectivity of the transduction channels in the hair cells of the frog sacculus. 1995

F Jørgensen, and A B Kroese

IMB, Department of Physiology, Odense University, Denmark.

The extracellular receptor currents evoked by step displacements of the otolithic membrane of the isolated saccular macula of Rana esculenta were recorded under transepithelial voltage clamp conditions. With the aim to depolarize the hair cells and increase the fractional resistance of the apical membranes, the basal side of the preparation was bathed in saline with an increased K+ concentration (62 mM). This caused a shift in the non-linear receptor current-voltage relation along the voltage axis of -51 mV +/- 10 mV; (mean +/- SD; n = 32) and a reduction in the transepithelial resistance of 10%. Under these conditions the electrical properties of the macula are assumed to be controlled by the apical membranes. The effects of different concentrations of Ca2+ in the apical solution on the receptor current-voltage relation were examined. Change of the apical Ca2+ concentration (range 3 mM to 70 microM) varied the transepithelial voltage at which the receptor current was zero (Vrev). Fitting a modified constant field equation to the relation between the apical Ca2+ concentration and the change in Vrev gave an estimate of PCa/PK of the transduction channels of 212. Furthermore, a high relative permeability of the transduction channels for other divalent cations (Ba2+, Sr2+) was measured, whereas Mn2+ inhibited the receptor current. The receptor current was inhibited by amiloride (IC50 3.2 microM +/- 1.7 microM) and nifedipine (IC50 1.9 microM +/- 0.6 microM). Reduction of the apical Ca2+ concentration to 90 microM in standard apical solution reduced the size of the receptor current to 67% +/- 30% (n = 17) compared to control but did not affect the shape of the receptor current-voltage relation. Subsequent substitution of K+ by Na+ caused a further reduction of the receptor current to 32% +/- 29% (n = 9), changed the receptor current-voltage relation into a linear relation and diminished the adaptation of the receptor current. These results indicate that the mechano-electrical transduction channels of the frog saccular hair cells are highly selective to Ca2+ and that the conductance of the channels may be influenced by the apical monovalent cation species.

UI	MeSH Term	Description	Entries
D010477	Perfusion	Treatment process involving the injection of fluid into an organ or tissue.	Perfusions
D010812	Physical Stimulation	Act of eliciting a response from a person or organism through physical contact.	Stimulation, Physical,Physical Stimulations,Stimulations, Physical
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.
D011893	Rana esculenta	An edible species of the family Ranidae, occurring in Europe and used extensively in biomedical research. Commonly referred to as "edible frog".	Pelophylax esculentus
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
D004594	Electrophysiology	The study of the generation and behavior of electrical charges in living organisms particularly the nervous system and the effects of electricity on living organisms.
D005110	Extracellular Space	Interstitial space between cells, occupied by INTERSTITIAL FLUID as well as amorphous and fibrous substances. For organisms with a CELL WALL, the extracellular space includes everything outside of the CELL MEMBRANE including the PERIPLASM and the cell wall.	Intercellular Space,Extracellular Spaces,Intercellular Spaces,Space, Extracellular,Space, Intercellular,Spaces, Extracellular,Spaces, Intercellular
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
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
D012444	Saccule and Utricle	Two membranous sacs within the vestibular labyrinth of the INNER EAR. The saccule communicates with COCHLEAR DUCT through the ductus reuniens, and communicates with utricle through the utriculosaccular duct from which the ENDOLYMPHATIC DUCT arises. The utricle and saccule have sensory areas (acoustic maculae) which are innervated by the VESTIBULAR NERVE.	Otolithic Organs,Utricle,Saccule,Organ, Otolithic,Otolithic Organ,Saccules,Utricle and Saccule,Utricles