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Results for “SEMICIRCULAR CANALS”

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At least 541 records · Page 30Linked to original sources
PubMed1993

Effects of extracellular ATP on hair cells isolated from the guinea-pig semicircular canals.

Externally applied ATP (100 microM) induced membrane currents in type I and type II vestibular hair cells enzymatically isolated from guinea-pig semicircular canals. In whole-cell voltage-clamp and with 140 mM K+ in the pipette solution, ATP evoked an inwardly directed current in 58% of the cells when held at potentials below -40 mV. In the remainder, external ATP produced an outward current. After block of the K currents, an inward current activated by ATP was revealed at -50 mV. Intracellular Ca2+ levels were monitored using the Ca2+ indicator Fura-2 and were found to rise in both hair cell types in response to ATP. These results strongly suggest that ATP directly controls the entry of Ca2+ into crista hair cells which can then further modulate K+ currents.

Adenosine Triphosphate↗
PubMed2001

Dynamics of intracellular calcium in hair cells isolated from the semicircular canal of the frog.

Changes in cytosolic free Ca(2+) concentration ([Ca(2+)]i) were monitored optically in hair cells mechanically isolated from frog semicircular canals using the membrane-impermeant form of the Ca(2+)-selective dye Oregon Green 488 BAPTA-1 (OG, 100 microM). Cells stimulated by depolarization under whole-cell voltage clamp conditions revealed Ca(2+) entry at selected sites (hotspots) located mostly in the lower (synaptic) half of the cell body. [Ca(2+)]i at individual hotspots rose with a time constant tau1 approximately 70 ms and decayed with a bi-exponential time-course (tau2 approximately 160, tau3 approximately 2500 ms) following a 160 ms depolarization to -20 mV. With repeated stimulation [Ca(2+)]i underwent independent amplitude changes at distinct hotspots, suggesting that the underlying Ca(2+) channel clusters can be regulated differentially by intracellular signalling pathways. Block by nifedipine indicated that the L-type Ca(2+)channels are distributed at different densities in distinct hotspots. No diffusion barrier other than the nuclear region was found in the cytosol, so that, during a prolonged depolarization (lasting up to 1s), Ca(2+) was able to reach the cell apical ciliated pole. The effective Ca(2+) diffusion constant, measured from the progression of Ca(2+) wavefronts in the cytosol, was approximately 57 microm(2)/s. Our results indicate that in these hair cells, buffered diffusion of Ca(2+) proceeds evenly from the source point to the cell interior and is dominated by the diffusion constant of the endogenous mobile buffers.

Animals↗
PubMed1977

Semicircular canal radii of curvature (R) in cat, guinea pig and man.

The radii of curvature (R) of the horizontal (Rh), anterior (Ra) and posterior (Rp) semicircular canals were measured by a new technique (called ROTA) for cat, guinea pig and man. For each canal, data points from the osseous canal were rotated and plotted by computer such that the plane of the sheet of computer plot corresponded to the plane best fitting that canal. The radius of each osseous canal was determined and where necessary, the radius of the arc of data points was corrected for thickness of the absent tissue. For cat, guinea pig and man there are differences in R between canals within a labyrinth suggesting that if other things are equal there could be differences in the average mechanical sensitivity of the canals, which is consistent with physiological recordings from primary vestibular neurons in the cat. The Rs determined by ROTA are compared with Rs determined by conventional histological means.

Action Potentials↗
PubMed2004

Head impulse test reveals residual semicircular canal function after vestibular neurectomy.

Meniere disease patients sometimes report vertiginous Meniere attacks after vestibular neurectomy that spares hearing. To determine why, the authors compared postsurgical semicircular canal function in nine patients with preserved hearing with that of a control group with no preservation of hearing. The three-dimensional head impulse test revealed residual posterior canal function in all patients with vertigo attacks (eight). The control patients had no residual canal function. Thus, residual vestibular function on the ipsilesional side may cause vertiginous Meniere attacks.

Adult↗
PubMed1996

[Wegener granulomatosis: a clinical case with parossistic positional vertigo due to involvement of the lateral semicircular canal].

The ear is involved in more than 20% of all cases of Wegener Granulomatosis (W.G.): such involvement takes place either through direct proliferation of the necrotic-granulomatosis tissue in the middle ear, or is a consequence of perieustachian tube infiltration from the rhinopharnyx. The inner ear is affected later and it is not clear as to exactly how. The present paper deals with the case of a 63-year-old woman who had a year been suffering from bilateral ear pain, and persistent otorrhea with typical signs of purulent chronic middle-ear otitis. During the course of the illness the patient complained of atypical paroxymal positional vertigo, compatible with cupulolithiasis of the semi-circular horizontal canal (as per E.N.G. recording). Transoral biopsy of the rhinopharynx and of the left nasal fossa revealed histopathological signs compatible with W.G.. In the light of post-mortem temporal bone studies performed by Friemann and Blatt on W.G. patients the present case could lead to further studies regarding the advancement of this pathological process within the middle and inner ears and the etiopathogenetic mechanisms involved. In particular, during the course of W.G., the appearance of benign paroxymal positional vertigo through cupulolithiasis of the semicircular horizontal canal may be justified: a) by the progressive involvement of the posterior labyrinth structures affecting the semicircular canals prior to the lateral canal and running on to the posterior canal; b) by the discovery of proteiform material in the labyrinthine fluids.

Cerebrospinal Fluid Otorrhea↗