[A concomitant operation of Damus-Kaye-Stansel procedure, atrioventricular valvuloplasty and total cavopulmonary connection]

A 2-year-old girl with single ventricle and coarctation of aorta, who received subclavian flap aortoplasty and pulmonary artery banding at 30 days of age, developed subaortic stenosis and atrioventricular valve regurgitation. At the age of 2 years and 10 months, physiologic correction with atrioventricular valvuloplasty, Damus-Kaye-Stansel procedure, and total cavopulmonary connection were performed concomitantly. She showed uneventful convalescence, and postoperative cardiac catheterization revealed trivial atrioventricular valve regurgitation with a mild pressure gradient between the left ventricle and aorta.

[Anorexia nervosa complicated with pulmonary tuberculosis]

A study was made on a patient with anorexia nervosa complicated with pulmonary tuberculosis treated with intravenous hyperalimentation (IVH). A 24-year-old female was admitted to our hospital because of progressive loss of body weight during medication for pulmonary tuberculosis at another hospital. She was diagnosed as having anorexia nervosa. After the nutritional assessment IVH was performed. As a result of IVH, her body weight increased and her nutritional deprivation, (i.e., low visceral proteins, low branched amino acids, etc.) recovered. Nutritional support was effective upon treating pulmonary tuberculosis.

Bioceramic implantation in the intermandibular space in bilateral rostral mandibulectomy of the dog

Effect of bioceramic implantation on the intermandibular space along with plating in rostral mandibulectomy was investigated in the dog. In this group, bioceramic beads consisting of a complex of hydroxyapatite and tricalcium phosphate were implanted in the intermandibular space between the lingual surfaces of the fracture ends. In two other groups, the dogs received only plating on the ostectomized end, or they received only rostal mandibulectomy without plating. No difficulty in mastication was observed in the implanted group after surgery. In the dogs which received plating, however, difficulty was noted only in the 4th week when wet food was replaced by dry food, and in the control group in the 6th week after the surgery. From the radiological and microscopical findings, in dogs with only plating or without the fixation there was no bony union in the intermandibular space at 16 weeks, though the increase in fibrous tissue and bony callus in the area was much greater in the plated dogs than in the control group. In the implanted group, on the other hand, the increase in callus formation was considerable compared to the other groups. Moreover, the lingual surfaces of the fracture ends were well ossified at 12 postoperative weeks. This suggests that in canine bilateral rostral mandibulectomy the stabilization of the fracture ends with plates and bioceramic implants filling a gap in the intermandibular space may enhance the ossification between the fracture ends and prevent postoperative difficulty in mastication.

Hematoma enlargement in spontaneous intracerebral hemorrhage

In order to evaluate the incidence and risk factors of hematoma enlargement in spontaneous intracerebral hemorrhage (ICH), 419 cases of ICH were reviewed. The first computerized tomography (CT) scan was performed within 24 hours of onset and the second within 24 hours of admission; a blood sample was taken for laboratory examination within 1 hour of admission. In 60 patients (14.3%) the second CT scan showed an enlarged hematoma. The incidence of enlargement significantly decreased with time (p < 0.05) and significantly increased with the severity of liver dysfunction and the volume of the hematoma on the first CT scan. Patients with an irregularly shaped hematoma had a higher risk of hematoma growth than those with a round hematoma. In addition, patients with hematoma enlargement were more likely to have coagulation abnormalities (low platelet counts and low levels of fibrinogen, alpha 2-antiplasmin activity and platelet aggregation). Moreover, hematoma growth was associated with a poor clinical outcome. It is concluded that patients admitted to a hospital within 6 hours of onset of ICH, especially those admitted within 2 hours, and patients with liver dysfunction or irregularly shaped large hematomas should be closely observed for at least 6 hours after onset in preparation for emergency surgery, since the risk of hematoma growth in these circumstances is high.

Thapsigargin, a Ca(2+)-ATPase inhibitor, relaxes rat aorta via nitric oxide formation

Thapsigargin induced endothelium-dependent relaxation and cGMP production in rat thoracic aorta, and these effects were inhibited by nitric oxide (NO) pathway inhibitors, a calmodulin inhibitor and removal of Ca2+, suggesting that NO is involved in the thapsigargin-induced relaxation. Thapsigargin may deplete Ca2+ stores in the endothelial cells by inhibiting the Ca(2+)-ATPase, a Ca2+ pump, which in turn triggers influx of extracellular Ca2+, leading to activation of constitutive NO synthase and resultant NO generation. The NO thus formed may activate soluble guanylate cyclase to produce cGMP in the vascular smooth muscle.

Heparin administration and monitoring for neuroangiography

PURPOSE

To establish the optimal protocol of heparin administration during interventional neuroradiology.

METHODS

We assessed 100 cases of neuroangiography, including endovascular surgery, and measured activated coagulation time before and 5 minutes after heparin administration, and before and 5 minutes after protamine neutralization. In some cases actual heparin concentration was assayed using a chromogenic substrate technique.

RESULTS

The actual plasma heparin concentration significantly correlated with the dose of heparin administered intravenously (r = .98; P < .0001) and changes in activated coagulation time (r = .85; P < .0001). The change in activated coagulation time significantly correlated with the dose of heparin injected intravenously (r = .54, P < .0001). The ratio of change in activated coagulation time significantly correlated with time elapsed after heparin administration (r = -.70, P < .0001).

CONCLUSIONS

The activated coagulation time is useful in monitoring administration and neutralization of heparin during neuroangiography, and a bolus injection of 60 U/kg heparin should be adequate to carry out neuroangiography for 75 minutes safely, even for endovascular surgery.

[A comparative study among ftorafur, ftorafur plus tamoxifen, and tamoxifen in adjuvant therapy for breast cancer. The Chubu Cooperative Study Group of Adjuvant Chemoendocrine Therapy for Breast Cancer, Japan]

A randomized study assessing the efficacy of three treatment of ftorafur (FT), ftorafur plus Tamoxifen (TAM), and Tamoxifen in patients diagnosed as having stage II (N1b) or stage III breast cancer was carried out at 90 institutions in the Chubu district of Japan. After 10 mg of MMC administration on the day of surgery and the next day, patients were allocated to one of three treatments: FT 600 mg/day for 2 years, FT 600 mg/day plus TAM 20 mg/day for 2 years, or TAM 20 mg/day for 2 years. A total of 647 cases were analyzed. No significant differences were observed in the 5-year disease-free survival rates or in the 5-year survival rates. In the stratified analysis, however, a beneficial effect of adding FT to TAM was observed in the patients with ER-positive tumors in the 5-year survival rate, and FT plus TAM treatment was favorable compared with the other two treatments for postmenopausal patients with ER-positive tumors.

Malignant paraganglioma presenting as Cushing syndrome with virilism in childhood. Production of cortisol, androgens, and adrenocorticotrophic hormone by the tumor

BACKGROUND

A 12-year-old girl with intractable retroperitoneal paraganglioma experienced increased appetite, acne, obesity, "moon face," and enlargement of the clitoris during the course of the tumor. Plasma cortisol, serum testosterone, and dehydroepiandrosterone sulfate (DHEA-S) levels were increased to 34.1 micrograms/dl, 2.0 ng/ml, and 6.628 ng/ml, respectively. Adrenocorticotrophic hormone (ACTH) levels were not increased, and results of dexamethasone suppression tests were negative. Her condition was diagnosed as Cushing syndrome with virilism. Plasma cortisol levels were increased to a level of 107.1 micrograms/dl before death.

METHODS

Tumor samples were obtained at the time of autopsy. The concentrations of cortisol, androgens, ACTH, and catecholamines were assayed in the tumor extracts. The indirect immunoperoxidase procedure was performed on fixed tissues for cortisol, DHEA-S, testosterone, and ACTH.

RESULTS

Extracts of the tumor masses contained steroid hormones: the amount of immunoreactive cortisol was 1.64 micrograms/g wet weight; the amount of immunoreactive testosterone was 25.60 ng/g wet weight; immunoreactive DHEA-S, 579.00 ng/g wet weight; and immunoreactive ACTH, 891.00 pg/g wet weight in the metastatic mass of the lung. Immunohistochemically, immunoreactive cortisol, testosterone, and DHEA-S were detectable in the tumor cells. The adrenal gland was atrophic.

CONCLUSIONS

The patient is the first reported with malignant paraganglioma with the capacity to produce cortisol, androgens, and ACTH.

[A clinical study of chronic lower respiratory tract infections with Pseudomonas aeruginosa by transtracheal aspiration]

We investigated the yearly changes of the incidence of Pseudomonas aeruginosa (P. aeruginosa) isolated from chronic lower respiratory tract infections (CLRTI), and also performed a clinical study on CLRTI with P. aeruginosa by transtracheal aspiration (TTA) to clarify the recent trend of P. aeruginosa infection in CLRTI and the predisposing clinical factors to the acute exacerbation. The isolation rate of P. aeruginosa among the total isolated bacteria in CLRTI between December 1978 and March 1983 was 8.4%, but it increased to 23.1% between April 1988 and March 1993. In 69 episodes (40 cases) of P. aeruginosa isolated from CLRTI between April 1983 and March 1993, monomicrobial infections of P. aeruginosa were 42 episodes (60.9%) and polymicrobial infections were 27 episodes (39.1%). When the diseases were classified into acute exacerbated and non-exacerbated phases, polymicrobial infections were seen more in the former phase, and the principal organisms detected with P. aeruginosa were Haemophilus influenzae and Streptococcus pneumoniae. In the acute exacerbated cases, predisposing conditions concerning the exacerbation were divided into four patterns: 1. polymicrobial infections with H. influenzae or S. pneumoniae, 2. after acute upper respiratory tract infections due to viral superinfection, 3. early phase from bacterial replacement by P. aeruginosa, 4. immunocompromised states such as adrenal corticosteroid administration or systemic underlying diseases. These results suggest that the importance of P. aeruginosa in CLRTI is increasing year by year and we must pay attention to the fact that P. aeruginosa alone may also cause acute exacerbation in the latter 2 patterns of the condition.

Effect of LC9018 combined with radiation therapy on carcinoma of the uterine cervix. A phase III, multicenter, randomized, controlled study

BACKGROUND

The failure rate with radiation therapy alone for Stage III cervical cancer is quite high, and therefore other modalities are being pursued as adjuvants to radiation therapy in hopes of improving the results.

METHODS

A randomized, controlled, comparative study on the efficacy and safety of radiation therapy combined with LC9018 (a biologic response modifier prepared from heat-killed Lactobacillus casei YIT9018) was conducted using 228 patients with Stage IIIB cervical cancer.

RESULTS

LC9018 enhanced tumor regression (P < 0.1) by radiation after both 30 Gy of external radiation and at the completion of radiation therapy. The combination therapy also prolonged survival and the relapse-free interval (P < 0.05) compared to radiation alone. Analysis of survival using the Cox proportional hazard model indicated that use of LC9018 was a significant factor related to survival duration. Major side effects of combined LC9018 included fever and skin lesions at the injection site, but no severe symptoms were noted. Radiation-induced leukopenia was significantly less severe (P < 0.05) in the LC9018-combined group than in the radiation-alone group, suggesting that this agent might help to prevent leukopenia during radiation therapy.

CONCLUSIONS

LC9018 was shown to be an effective agent for adjuvant immunotherapy when combined with radiation therapy.

Two types of chloride channel in the basolateral membrane of vestibular dark cells

Transepithelial and cell membrane potential measurements have suggested that the basolateral membrane of gerbil vestibular dark cells contains Cl- conductive pathways. We used the patch clamp technique to search this membrane for Cl- conductive channels which could account for the macroscopic observations. Two types of Cl- channel were found in both cell-attached and excised membrane patches. One type was found with an incidence of 19% and had a single-channel conductance of 95 +/- 1 pS (N = 20) in symmetrical Cl- solutions. The other type was found with an incidence of 3% and had a large single-channel conductance of 360 +/- 11 pS (N = 12) in symmetrical Cl- solutions (LC-type Cl- channel). Both types of Cl- channel had linear current-voltage relations and at least 2 substates. In asymmetrical Cl- solutions (gluconate substitution) the current-voltage relations fit the Goldman-Hodgkin-Katz current equation for Cl-. Neither channel was blocked by Zn2+, NPPB, DIDS, DNDS or quinine. The 95 pS channel exhibited a spontaneous 'rundown' of its activity within 1 to 10 min after being excised. This rundown was not reversed by the catalytic subunit of protein kinase A. Channel activity was not dependent on the presence of cytosolic Ca2+ nor markedly altered by variations in cytosolic pH between 6.5 and 8.0. The two Cl- channels were distinguished by the membrane voltage ranges in which they were active and by their anion selectivity. The open probability of the 95 pS channel was insensitive to voltage and the anions NO3-, I- and Br- were only half as permeable as Cl-. By contrast, the LC-type Cl- channel was mostly active between about +/- 30 mV and equally permeable to NO3-, I-, Br- and Cl-. The 95 pS Cl- channel may account for the observed transepithelial and intracellular voltage responses to Cl- concentration steps and provide the path for the recirculation of Cl- across the basolateral membrane. The LC-type Cl- channel shows the same lack of anion discrimination as the anion pathway activated during hyposmotic challenge.

[Determination of neutrophil function in the respiratory infection by chemiluminescence (CL). I: Change in neutrophil's CL by chemotherapy against the bacterial pneumonia]

We measured neutrophil's CL (CL-index) in 12 patients of the bacterial pneumonia three times per each case: before, during and after chemotherapy. Before the initiation of chemotherapy. CL-index in the six patients remained higher than that in healthy controls, while the remaining six showed lower levels of CL-index compared to the controls. In the 11 cases, their CL-indexes fell to levels lower than those obtained before treatment. Additionally, in the 11 cases their CL-indexes increased after the termination of chemotherapy. Furthermore, in the nine cases the product of the neutrophil number and CL-index was decreased by chemotherapy, and the decrease in the product correlated with improvement in their clinical conditions.

Alterations of host response by a long-term treatment of roxithromycin

Roxithromycin (10 mg/kg) was administered once-daily for seven or 28 days to mice intragastrically and its effects on cytokine synthesis were studied. Administration of roxithromycin for 28 days resulted in increased synthesis of interleukin (IL)-1 and tumour necrosis factor (TNF-alpha) production by macrophages, and the production of IL-2, IL-4 and interferon gamma by splenocytes. In contrast, 7 day administration of roxithromycin did not affect these parameters. Furthermore, clindamycin treatment did not significantly increase the capacity of host cells to produce cytokines, irrespective of the duration of treatment, when compared with the solvent control receiving 0.9% ethanol solution or the untreated controls. In addition, the supernatant of a 7 day culture of splenocytes with roxithromycin showed suppression of the production of TNF-alpha and prostaglandin E2 by mitogen-stimulated macrophages, and this suppressive activity was impaired by a monoclonal antibody to murine IL-4. Thus, this data suggests that roxithromycin may not only enhance the host defence system through increased cytokine synthesis by host cells, but also exhibit anti-inflammatory activity by including an anti-inflammatory cytokine, IL-4.

[Effect of erythromycin on production of cytotoxin and attachment factors of bacteria]

We studied the effect of erythromycin (EM) on the attachment of Pseudomonas aeruginosa and Neisseria gonorrhoeae to HeLa and HT-177 cell and on cytotoxin production of P. aeruginosa. 1. EM inhibited attachment of these bacteria. 2. EM inhibited manifestation of the pili of these bacteria. 3. EM inhibited production of protein II, the second attachment factor of N. gonorrhoeae. 4. EM inhibited production of 66 K cytotoxin of P. aeruginosa. On the basis of these findings, it was suggested that EM might inhibit infection by repressing manifestation of the attachment factor and production of cytotoxin of the bacteria.

Serum cathepsin B levels and urinary excretion of cathepsin B in the cancer patients with remote metastasis

Serum cathepsin B levels and urinary excretion of cathepsin B in the cancer patients without remote metastasis were significantly higher than those in the control non-cancer patients. Moreover, these parameters in the cancer patients with remote (liver or lung) metastasis were significantly higher than those in the cancer patients without remote metastasis. After radical curative operations, these parameters were restored to the control values. These results suggest a possible role of lysosomal enzyme, cathepsin B in the pathogenesis of tumor metastasis, and also suggest that these parameters might be possible indicators for tumor malignancy such as remote metastasis.

[Morphological study on edentulous mandibula]

For the purpose of studying morphology of edentulous mandibula, not only the bone change of edentulous alveolar part, but the whole morphological change of edentulous mandibula was examined. Thirty-three edentulous mandibulae that have no sockets owing to the bone absorption of alveolar ridge and eighty dentulous mandibulae that possess no missing teeth except wisdom teeth were measured and compared. The authors obtained the following results concerning the morphological change of edentulous mandibula: 1. Although the body height was significantly low on account of bone absorption at the alveolar ridge, bone absorption at base of mandibula was not much observed. 2. Both condylar process height and coronoid process height were significantly low. 3. Mandibular angle of edentulous mandibular was greater. 4. In dentulous mandibula a negative correlation between mandibular angle and condylar process height, coronoid process height was found. A correlation between mandibular angle and the difference of total mandibular length and body length was observed. A great mandibular angle was found because it seems that the bone deposition was less at the inferior and posterior margin of mandibular angle part. 5. It seems that bone absorption at inferior and posterior margin of edentulous mandibular angle part was due to less bone deposition. Because a bite force decreased for missing teeth.

Aminoglycoside antibiotics inhibit maxi-K+ channel in single isolated cochlear efferent nerve terminals

Patch clamp recordings were obtained from isolated cochlear efferent nerve terminals. The effect of aminoglycoside antibiotics on single maxi-K+ channels was determined. At positive voltages (cytosol with respect to extracellular side), neomycin, streptomycin, and kanamycin significantly reduced the single channel current amplitude of the maxi-K+ channel from the cytosolic side. The IC50 for neomycin was 9.10(-4) M from the cytosolic side and >> 10(-3) M from the extracellular side. Streptomycin and kanamycin were less potent. No significant difference in inhibition of the single channel current amplitude by 2.5.10(-4) M cytosolic neomycin was observed between 7.10(-4) M and 10(-6) M free cytosolic Ca2+. Neomycin had no significant effect on the open probability of the maxi-K+ channel either from the cytosolic or from the extracellular side. These findings demonstrate that the maxi-K+ channel in cochlear efferent nerve terminals can be a site of action for aminoglycoside antibiotics.

[Age-related alterations in the mechanism of renovascular contractility in patients with essential hypertension]

Systemic hemodynamics and renal blood flow (RBF) were studied before and during isometric exercise (IE) in 48 hypertensive patients. Of the 48 hypertensives, 21 were unmedicated and the remaining 27 patients were given one of the following drugs for 3 days prior to the study: 15 patients were treated with Enalapril (5 mg/day) and 12 patients were treated with Bunazosin (2 mg/day). Cardiac output (CO) and RBF were measured simultaneously with two different thermodilutional catheters. To elucidate the influence of aging on the renovascular response to IE, each group was divided into younger (age > 50) and older (age > or = 50) subgroups. RBF decreased and calculated renovascular resistance (RVR) increased significantly during IE in the unmedicated group, but showed no difference in the degree of changes in these parameters between the younger and older subgroups. In the Bunazosin group, RBF and RVR did not change during exercise in either subgroups. In the Enalapril group, RBF did not change in either subgroup, and RVR increased significantly in the younger subgroup, but was unchanged in the older subgroup. There was a negative linear relationship between delta RVRI (change of RVR corrected by body surface area) and age (y = -0.15x + 9.7, r = -0.59: p < 0.05). Plasma norepinephrine increased after IE, but these changes were not significant in all 3 groups. These data suggest that the enhanced renovascular contractility during IE is accomplished mainly through alpha 1-adrenoceptor, and the responsiveness of alpha 1-adrenoceptor may decrease with age.(ABSTRACT TRUNCATED AT 250 WORDS)

[Clinical study of acute bacterial bronchitis]

Eighty-two episodes (77 cases) in which any pathogens were isolated from transtracheal aspiration (TTA) and which satisfied the new clinical criteria of acute bacterial bronchitis were clinically evaluated. Major pathogens isolated from TTA included H. influenzae, S. pneumoniae and B. catarrhalis. Fever developed in 91.5% of the patients. Sputum volume averaged 16.3 +/- 14.9 ml per day. All the patients suffered from coughs, which were so severe as to disturb sleep in 8.5% of the patients. Inflammatory indices included WBC 9738.0 +/- 3158.5/microliter, CRP 10.1 +/- 7.9 mg/dl and ESR 69.0 +/- 38.8 mm/hr on average, PaO2 fell in most cases. Compared to the group of patients with acute bacterial bronchitis from which a single pathogen was isolated, the numbers of elderly patients and smokers were significantly more in the group of multiple pathogens isolated from TTA. Prior episodes related to the development of acute bacterial bronchitis were upper respiratory inflammation in 46.3% and undergoing bronchoscopy in 4.9% of the patients. Antibiotics therapy cured acute bacterial bronchitis in 96.3% of the patients. In spite of treatment, 3 patients developed pneumonia and died.

[Pneumonia due to respiratory syncytial virus diagnosed by transtracheal aspiration in an adult]

A healthy-looking 44-year-old female was admitted to our hospital complaining of fever and hemosputum. The chest roentgenogram on admission showed patchy infiltrates of the segment 3 and 8 of the right lung. Laboratory studies showed a leukocyte count of 9700/microliters, erythrocytes sedimentation rate of 55 mm/hour and C reactive protein of 8.7 mg/dl. The arterial PO2 was 71.9 torr while the patient was breathing room air. Transtracheal aspiration was performed on admission, and strains and culture for bacteria, acid fast bacilli, fungi and mycoplasma were negative. Respiratory syncytial virus was isolated from transtracheal aspirates. The RSV complement fixing antibody titers rose from 1:40 to 1:16. She became afebrile on the fourth day after admission and her chest roentgenogram improved gradually. RSV infection should be considered in the differential diagnosis of atypical adult pneumonias.

[Clinical study of anaerobic respiratory infection]

This clinical study involved 35 cases, anaerobic bacteria were detected by TTA (transtracheal aspiration) or percutaneous lung aspiration, or pleural puncture. These cases were treated over the last 8 years in our department. There were 9 empyema, 9 pneumonitis, 5 lung abscess, 1 necrotizing pneumonia and 11 chronic lower airway infection. In 13 cases (37%), anaerobic bacteria alone were detected, whereas both anaerobic and aerobic bacteria were observed in the other 22 cases (63%). Of all bacteria detected. Bacteroids and Peptostreptococcus were the most common. With respect to host factors involved in the pathogenesis of pleural and parenchymal infection, aspiration was though to be a major trigger in only 11 out of the 24 cases (46%). The other 13 cases (54%) showed no evidence of aspiration, indicating that some other triggers was responsible. In further study, these 13 cases were found either to be heavy smokers with Brinkman index of more than 600, or to show sign of chronic lower airway infection. Both conditions were characterized by an inhibition of the mucociliary transport in the lower airway. Therefore, this study suggested that in the case without apparent aspiration the failure of local defense mechanisms in the airway, as a result of heavy smoking and/or chronic lower airway infection are involved in the pathogenesis of anaerobic respiratory infection.

Endothelin-3-induced relaxation of rat thoracic aorta: a role for nitric oxide formation

1. Endothelin-3 (ET-3) at concentrations below those which caused contraction (30 nM) elicited endothelium-dependent relaxation followed by rebound contraction in rat isolated thoracic aorta. 2. Endothelin-1 also relaxed the rat aorta with a similar potency. 3. The nitric oxide (NO) synthase inhibitor, NG-nitro L-arginine, the radical scavenger, haemoglobin and the soluble guanylate cyclase inhibitor, methylene blue, each inhibited the ET-3-induced relaxation. 4. The calmodulin inhibitor, calmidazolium, considerably attenuated the relaxation caused by ET-3 without affecting that to nitroprusside. 5. Concentrations of ET-3 that were necessary to induce the relaxation also caused concentration-dependent elevation of guanosine 3':5'-cyclic monophosphate (cyclic GMP) levels. 6. NG-nitro L-arginine, haemoglobin, methylene blue, calmidazolium and removal of the endothelium completely abolished ET-3-stimulated cyclic GMP production. 7. These results suggest that ET-3 triggers NO formation possibly via ETB receptors on the endothelium to activate soluble guanylate cyclase, which in turn stimulates cyclic GMP production and smooth muscle relaxation. The enzyme contributing to the NO formation may be of the calcium/calmodulin-dependent, constitutive type.

Maxi-K+ channel in single isolated cochlear efferent nerve terminals

Patch clamp recordings were obtained from isolated cochlear efferent nerve terminals. Channel activity was found in 85% of membrane patches, was present in on-terminal and excised patches and was characterized to originate from a maxi-K+ channel. An average of 2.0 +/- 0.1 (N = 33) maxi-K+ channels were found per active patch. In symmetrical solutions, the current-voltage relationship was linear and the single-channel conductance was 221 +/- 5 pS (N = 22). The open probability of the maxi-K+ channel increased with depolarization of the membrane potential and with an increasing free Ca2+ concentration on the cytosolic side. The open probability was insensitive to changes in the free Ca2+ concentration on the extracellular side. TEA (20 mM) and charybdotoxin (10(-7) M) decreased the open probability to nearly zero from the extracellular side but had no effect from the cytosolic side. The high incidence with which this channel was found suggests that the maxi-K+ channel is physiologically relevant which might include protection against overstimulation of the efferent synapse.