Takashi Kimitsuki

Mice lacking ganglioside GM3 synthase exhibit complete hearing loss due to selective degeneration of the organ of Corti

The ganglioside GM3 synthase (SAT-I), encoded by a single-copy gene, is a primary glycosyltransferase for the synthesis of complex gangliosides. In SAT-I null mice, hearing ability, assessed by brainstem auditory-evoked potentials (BAEP), was impaired at the onset of hearing and had been completely lost by 17 days after birth (P17), showing a deformity in hair cells in the organ of Corti. By 2 months of age, the organ of Corti had selectively and completely disappeared without effect on balance or motor function or in the histology of vestibule. Interestingly, spatiotemporal changes in localization of individual gangliosides, including GM3 and GT1b, were observed during the postnatal development and maturation of the normal inner ear. GM3 expressed in almost all regions of cochlea at P3, but at the onset of hearing it distinctly localized in stria vascularis, spiral ganglion, and the organ of Corti. In addition, SAT-I null mice maintain the function of stria vascularis, because normal potassium concentration and endocochlear potential of endolymph were observed even when they lost the BAEP completely. Thus, the defect of hearing ability of SAT-I null mice could be attributed to the functional disorganization of the organ of Corti, and the expression of gangliosides, especially GM3, during the early part of the functional maturation of the cochlea could be essential for the acquisition and maintenance of hearing function.

Cisplatin blocks mechano-electric transducer current in chick cochlear hair cells

The effects of cisplatin (cis-dichlorodiammine platinum II, CDDP) on the mechano-electrical transduction (MET) current were investigated with a whole-cell patch-electrode voltage clamp technique in dissociated cochlear hair cells of chicks. CDDP blocked the MET channel in a dose- and voltage-dependent manner. At -50 mV, CDDP blocked the MET channel with a Hill coefficient of approximately 2 and a dissociation constant (KD) of 1.5 x 10(-3) M. The kinetics of CDDP blockade consist of a voltage-independent and a voltage-dependent component.

Correlation between MRI Findings and Second-Look Operation in Cholesteatoma Surgery

Two-staged intact canal wall tympanoplasty is a common operation for treatment of middle ear cholesteatoma. MRI provides better tissue differentiation of the middle ear and/or mastoid, which often become occupied with soft density tissue after the first operation. If MRI was able to detect the presence of a recurrent or residual cholesteatoma with sufficient sensitivity and specificity, this may facilitate a decrease in the number of second-look procedures. This study compared MRI findings to surgical findings at second-look surgery and calculated the correlation rates between the two sets of findings. Thirty ears having undergone intact canal wall tympanoplasty for cholesteatoma at the initial operation were examined by MRI prior to the second look. Otoscopic findings of the tympanic membrane were nonsuspect in all cases. The true positive rate was 11/30 (37%) and the true negative rate was 10/30 (33%), leading to a radiosurgical correlation of 70%, whereas the false positive rate was 6/30 (20%) and the false negative rate was 3/30 (10%). This indicates that 30% of the MRI findings were incorrect. Therefore, at the present time, MRI does not appear as a likely replacement for second-look surgery in cases of intact canal wall tympanoplasty.

Dihydrostreptomycin modifies adaptation and blocks the mechano-electric transducer in chick cochlear hair cells

Block of the mechano-electric transduction (MET) channel by dihydrostreptomycin (DHSM) and its effects on adaptation were investigated in dissociated cochlear hair cells of the chick with a whole-cell patch-electrode voltage clamp technique. DHSM reversibly blocked the MET channel in a dose- and voltage-dependent manner. At -50 mV, DHSM blocked the MET channel with a Hill coefficient of approximately 1 and a dissociation constant (Kd) of 2 x 10(-5) M. Rate constants for the DHSM to bind and to unbind to and from the channel were estimated, and could be larger than 5 x 10(7) M-1.s-1 and 1 x 10(3) s-1, respectively. The amplitude of MET current decreased during a constant displacement of the hair bundle. This current decay, the adaptation, disappeared in the DHSM medium. The disappearance and the emergence of adaptation did not have a simple relationship with the block of MET channel by DHSM, but appeared with some delay.

Voltage-dependent Ca2+ channels in the spiral ganglion cells of guinea pig cochlea

Voltage-dependent Ca2+ channels in spiral ganglion cells (SGCs) isolated from guinea pig cochlea were investigated using the patch-clamp technique in a whole-cell recording mode. The voltage-dependent Na+ and K+ currents were blocked by adding tetrodotoxin, 4-aminopyridine, and tetraethylammonium to the external solution and by using choline or Cs+ in the external and internal solutions instead of Na+ or K+, respectively. The depolarizing voltage steps evoked inward currents with slow current decay. The maximum amplitude of the inward current increased in a hyperbolic manner with increasing extracellular Ca2+ concentration, indicating that the inward current was a voltage-dependent Ca2+ current (ICa). In 5 mM Ca2+ external solution, the ICa activated from a membrane potential around -60 mV and reached full activation at about -10 mV. The ICa inactivated from about -60 mV and became fully inactivated at about O mV, consistent with the high-voltage-activated Ca2+ channel subtype. Ionic selectivities for Ca2+ channels in SGCs were as follows: Ca2+ > Ba2+ > Sr2+. Effects of both inorganic and organic Ca2+ antagonists also were examined. The inhibitory strength was as follows: La3+ > Cd2+ > Ni2+ > or = Co2+ for inorganic Ca2+ antagonists, and flunarizine > nicardipine > methoxyverapamil > diltiazem for organic ones.

Disturbance of Regulation of Sodium by CIS-Diamminedichloroplatinum in Perilymph of the Guinea Pig Cochlea

We studied the acute effects of cis-diamminedichloroplatinum (CDDP) on the cochlear partition and inner ear fluid in the guinea pig. At 48 hours after the administration of a single intramuscular injection of CDDP, 12.5 mg/kg of body weight, the endocochlear resting potential (EP) was significantly decreased to 32.1 ± 1.8 mV in the treated animals, versus 80.6 ±.1.0 mV in the control animals. There was a significant rise in potassium (K+), sodium (Na+), and chlorine (Cl−) in the endolymph of the animals treated with CDDP as compared with the control animals. Only Na+ was found to increase significantly in the perilymph, reaching more than twice the level of the control animals; both K+ and Cl− remained within the normal range. Serum electrolytes also remained within the normal range. Evaluation of modified ionic permeabilities across the endolymph-perilymph barrier showed an apparent increase in Na+ permeability and a normal range of K+ and Cl− permeabilities. Histopathologic examination of the cochlea showed a moderate collapse of the endolymphatic space, with atrophy of the stria vascularis and destruction of the outer hair cells. The findings suggest that the acute changes produced in the cochlea by administration of CDDP were attributable to a breakdown in the regulation of Na+ metabolism in the perilymph.

Huge hamartoma with inverted papilloma in the nasal cavity

Abstract We report clinical experience in managing a 46-year-old Japanese man with long-standing nasal obstruction resulting from a huge left nasal mass. Computed tomography, magnetic resonance imaging and biopsy were used to make a provisional diagnosis of inverted papilloma. The mass was resected via a frontal approach combined with rhinotomy. Histopathologic examination of the resected specimen was consistent with a hamartoma that included an inverted papilloma on a portion of its surface. In addition to being rare tumors in the nasal cavity, we believe that our patient’s tumor the largest nasal hamartoma ever reported.

Single Channel Recordings of Calcium Currents in Chick Cochlear Hair Cells

Single Ca2+ channel currents were recorded from chick cochlear hair cells by using cell-attached patches. The elementary current was about -2 pA at 70 mV positive to the resting potential (R.P.+ 70 mV); the slope conductance over a 40 mV voltage range was 24 pS. The open time histogram was reasonably well expressed by a single exponential function, while the closed time histogram was expressed by a sum of two exponential functions. The Ca2+ channel was activated around R.P.+ 60 mV and the average ensemble current did not decay during 130 ms depolarization, suggesting that the Ca2+ channel in chick cochlear hair cells is the L-type. The Ca2+ channel has three modes of gating behaviour, expressed as current records with brief openings (mode I), no openings (mode 0), or long-lasting openings and very brief closings (mode 2).

Histochemical localization of the extracellular matrix components in the annular ligament of rat stapediovestibular joint with special reference to fibrillin, 36-kDa microfibril-associated glycoprotein (MAGP-36), and hyaluronic acid

The annular ligament across the stapediovestibular joint connects the stapes footplate and the vestibular window and plays an important role in the sound conductive system of the ear. In this study, we investigated the distribution of extracellular matrix components in the ligament by histochemical methods at light and electron microscopic levels. As results, light microscopic immunohistochemistry of fibrillin and 36-kDa microfibril-associated glycoprotein (MAGP-36) showed intense immunoreactivities in the annular ligament between the stapes footplate and vestibular window. In addition, the histochemical localization of hyaluronic acid by using biotinylated hyaluronic acid-binding protein (HABP) clarifi ed the presence of hyaluronic acid in the annular ligament. At the electron microscopic level, the immunogold labeling of fibrillin showed intense labeling on the periphery of the electron-dense mantle. Furthermore, the labeling of fibrillin was preferentially seen on the fibrous components among the electronlucent amorphous substance. The immunogold labeling of MAGP-36 was seen on the electron-dense mantle and scattered on the electron-lucent amorphous substance. The gold labeling with biotinylated HABP clearly showed a distribution of hyaluronic acid throughout the amorphous space in the ligament. The present results provide a histochemical profile of the annular ligament of the rat stapediovestibular joint that may provide clues to elucidation of pathological changes in the ligaments and conductive hearing loss in humans.

Potassium current properties in apical and basal inner hair cells from guinea-pig cochlea

Inner hair cells (IHCs) of guinea-pigs were separately isolated from the apical and basal turn and the potassium currents were measured by the whole-cell voltage-clamp technique. The potassium current flows through two types of membrane conductance: a fast (I(k,f)), tetraethylammonium (TEA)-sensitive conductance and a slow (I(k,s)), TEA-resistant conductance. Membrane conductance demonstrated no significant differences between apical IHCs and basal IHCs. Reversal potentials were -65+/-2 mV and -68+/-5 mV in apical and basal IHCs, respectively. The rate of outward current activation was voltage dependent and faster in basal IHCs than in apical IHCs. TEA effect was stronger on basal IHCs than on apical IHCs, suggesting that I(k,f) is dominant in basal IHCs.