Profiles of resting potentials across the stria vascularis in kanamycin-deafened guinea pigs.

The resting potentials of the marginal cells in the stria vascularis of the guinea pig were determined from changes in the combined electrode-tissue resistance of the electrode. The resistance of the electrode was 45.5 +/- 16.0 M omega (n = 20) before penetration of the stria vascularis and 46.7 +/- 17.3 M omega (n = 20) after penetration. The resistance drops across the luminal membrane of the marginal cells were 46.0 +/- 22.6 M omega (n = 12) in kanamycin-deafened guinea pigs and 54.5 +/- 33.1 M omega (n = 9) in normal guinea pigs. The endocochlear potential (EP) and resting potentials in the marginal cells were 90.1 +/- 6.0 mV (n = 14) and 70.4 +/- 11.3 mV (n = 14) in kanamycin-deafened guinea pigs and 84.8 + 5.1 mV (n = 29) and 74.7 +/- 11.7 mV (n = 29) in normal guinea pigs. The resting potentials in the marginal cells decreased gradually and were approximately 0 mV around 20 min after anoxia in both kanamycin-deafened and normal guinea pigs. These changes were comparable to those of EP in kanamycin-deafened guinea pigs during anoxia. The mechanism of the EP in kanamycin-deafened guinea pigs is discussed.

Malignant oncocytoma of the parotid gland: a case report with an immunohistochemical and ultrastructural study.

A rare case of a 71-year-old man with malignant oncocytoma is presented. The tumour was found in the left parotid region with enlarged lymph nodes in the neck. The resected parotid mass consisted of three discrete nodules, each histologically characterized by a uniform proliferation of oncocytic tumour cells. The patient underwent repeated operations for recurrences and metastases, and eventually died of acute pneumonia 18 months after the first admission. Metastases to the lymph nodes, ribs, spine and liver had been clinically pointed out. Immunohistochemically, the tumour cells were positive for alpha-1-antitrypsin, alpha-1-antichymotrypsin, lactoferrin, secretory component and carcinoembryonic antigen (CEA), while they were negative for S-100 protein and HHF35 (muscle specific actin). Ultrastructural pictures disclosed numerous mitochondria in the cytoplasm of the tumour cells, revealing neither myofibrils nor secretory granules. These findings therefore support the concept that this tumour is of a glandular epithelial origin.

Interlay method for myringoplasty.

Sixty-nine ears with perforation of the tympanic membrane were reviewed. All had undergone myringoplasty by the interlay method. The average period for complete epithelization was 16.1 days after surgery. Neither blunting of the anterior tympanomeatal angle nor lateralization of the tympanic membrane was observed. The success rate was 94.2% for the initial surgery, when "success" is defined as closure of the perforation and complete epithelization (dry ear). The surgical technique and various advantages of the interlay method of myringoplasty are described.

Importance of atticotomy in chronic otitis media with fixation of ossicles.

Seventy-seven patients with chronic otitis media were reviewed. Of the 77 patients, 42 underwent tympanoplasty with a columella, and 35 underwent myringoplasty and atticotomy. Twenty-five of the latter 35 patients showed less than 10 dB of hearing improvement with a patch test before operation. The ossicular chain was not disconnected in any of the 25 patients, but the mobility was severely restricted. It was interesting that fixation of the malleus was found at surgery in 80% (20/25) of the patients, whereas the stapes was immobilized in only 16% (4/25). Myringoplasty and atticotomy instead of tympanoplasty with a columella was sufficient to achieve hearing improvement in most of such cases. However, conventional atticotomy was not able to achieve improvement in the mobility of the ossicles because the mobility is usually severely restricted at the malleus. Removal of the anterior tympanic spine is the key to recovery of the mobility of the malleus, resulting in hearing improvement. Rate of success was obtained in 24 of 25 ears (96%).

Ototoxic effect of potassium canrenoate on the guinea pig cochlea.

Potassium canrenoate (PC) is a diuretic with antialdosterone action, reducing the reabsorption of sodium in the efferent renal tubules. This drug has been reported to damage only the marginal cells of the stria vascularis in the cochlea. The perilymphatic space of the guinea pig cochlea was perfused with an artificial perilymph containing 5 x 10(-3) M potassium canrenoate. Following the onset of perfusion, the endocochlear dc potential (EP) gradually declined to around 10 mV but did not become negative even when the perfusion was continued. A similar decrease in EP was observed in kanamycin-deafened guinea pigs. When the respirator was turned off and perfusion discontinued, a large negative EP appeared during 5 min of anoxia in normal guinea pigs but not in the kanamycin-deafened guinea pigs. The decreased EP recovered to preanoxic level after resumption of ventilation. The cochlear microphonics (CM) also gradually declined in parallel with the EP. The summating potential (SP) showed only a minor change. The potassium ion activity in the endolymph decreased slightly but the sodium ion activity remained unchanged during perfusion. These findings suggest that the main target of the PC is the cells of the stria vascularis.

[Effect of potassium canrenoate on the EP and Na+, K+ activities in endolymph].

The perilymphatic space was perfused with artificial perilymph containing 5 x 10(-3)M potassium canrenoate. The EP, K+ and Na+ activities in the scala media were measured with double barrelled K+ or Na+ selective microelectrode. Following the onset of the perfusion, the EP gradually declined and was stable after about 20 minutes. K+ activity also declined gradually but Na+ activity was unchanged. When the EP became stable, the artificial ventilation was stopped. The EP dropped to a large negative potential and K+ activity decreased gradually, but Na+ activity increased by degrees. The same results were observed in the untreated animals when the ventilation was stopped. There are no pathological changes both in the TEM view of the stria vascularis and in the SEM view of the hair cell. These results suggest that this drug may affect K+ conductance of the stria vascularis specifically.

Susceptibility of the endocochlear potential to pH and osmolarity changes in the perilymph of the cochlea in the guinea pig.

The effects of artificial perilymph at various pH levels and osmolarities on the endocochlear potential (EP) were investigated in a guinea pig model. In 47 ears, the mean EP was 74.5 +/- 0.5 mV in the second turn of the cochlea before perilymphatic perfusion. The artificial perilymph with a pH ranging from 5 to 9 and tonicity less than 1.25 (osmolarity, 345 mosmol/l) did not alter the EP when testings were recorded for at least 1 h. However, after the start of a perfusion with a pH less than 4, the EP declined gradually but recovered to the pre-perfusion level rapidly when the perfusion was stopped. The artificial perilymph with a pH over 10 decreased the EP considerably but showed no recovery, even after cessation of the perfusion. Tonicity more than 1.35 (osmolarity, 372.6 mosmol/l) also decreased the EP, with this decrease paralleling further increases in the tonicity used. From these data, we have concluded that a perilymph perfusate with a pH from 5 to 9 and an osmolarity less than 350 mosmol/l can be used in animal testing without any noxious effects on the EP.