[Clinical management and prognosis for descending necrotizing mediastinitis].

Objective: To investigate the clinical characteristics, treatment experiences and prognostic factors for descending necrotizing mediastinitis (DNM). Methods: A retrospective analysis was performed on the data of 22 patients with DNM diagnosed and treated in Henan Provincial People's Hospital from January 2016 to August 2022, including 16 males and 6 females, aged 29-79 years. After admission, all patients underwent CT scanning of the maxillofacial, cervical, and thoracic regions to confirm their diagnoses. Emergency incision and drainage were performed. The neck incision was treated with continuous vacuum sealing drainage. According to the prognoses, the patients were divided into cure group and death group, and the prognostic factors were analyzed. SPSS 25.0 software was used to analyze the clinical data. Rusults: The main complaints were dysphagia (45.5%, 10/22) and dyspnea (50.0%, 11/22). Odontogenic infection accounted for 45.5% (10/22) and oropharyngeal infection accounted for 54.5% (12/22). There were 16 cases in the cured group and 6 cases in the death group, with a total mortality rate of 27.3%. The mortality rates of DNM typeⅠand typeⅡwere respectively 16.7% and 40%. Compared with the cured group, the death group had higher incidences for diabetes, coronary heart disease and septic shock (all P<0.05). There were statistically significant differences between the cure group and the death group in procalcitonin level (50.43 (137.64) ng/ml vs 2.92 (6.33) ng/ml, M(IQR), Z=3.023, P<0.05) and acute physiology and chronic health evaluation Ⅱ(APACHEⅡ) score (16.10±2.40 vs 6.75±3.19, t=6.524, P<0.05). Conclution: DNM is rare, with high mortality, high incidence of septic shock, and the increased procalcitonin level and APACHE Ⅱ score combined diabetes and coronary heart disease are the poor prognostic factors for DNM. Early incision and drainage combined with continuous vacuum sealing drainage technique is a better way to treat DNM.

[Incidence and prognosis of olfactory and gustatory dysfunctions related to infection of SARS-CoV-2 Omicron strain: a national multi-center survey of 35 566 population].

Objective: This cross-sectional investigation aimed to determine the incidence, clinical characteristics, prognosis, and related risk factors of olfactory and gustatory dysfunctions related to infection with the SARS-CoV-2 Omicron strain in mainland China. Methods: Data of patients with SARS-CoV-2 from December 28, 2022, to February 21, 2023, were collected through online and offline questionnaires from 45 tertiary hospitals and one center for disease control and prevention in mainland China. The questionnaire included demographic information, previous health history, smoking and alcohol drinking, SARS-CoV-2 vaccination, olfactory and gustatory function before and after infection, other symptoms after infection, as well as the duration and improvement of olfactory and gustatory dysfunction. The self-reported olfactory and gustatory functions of patients were evaluated using the Olfactory VAS scale and Gustatory VAS scale. Results: A total of 35 566 valid questionnaires were obtained, revealing a high incidence of olfactory and taste dysfunctions related to infection with the SARS-CoV-2 Omicron strain (67.75%). Females(χ2=367.013, P<0.001) and young people(χ2=120.210, P<0.001) were more likely to develop these dysfunctions. Gender(OR=1.564, 95%CI: 1.487-1.645), SARS-CoV-2 vaccination status (OR=1.334, 95%CI: 1.164-1.530), oral health status (OR=0.881, 95%CI: 0.839-0.926), smoking history (OR=1.152, 95%CI=1.080-1.229), and drinking history (OR=0.854, 95%CI: 0.785-0.928) were correlated with the occurrence of olfactory and taste dysfunctions related to SARS-CoV-2(above P<0.001). 44.62% (4 391/9 840) of the patients who had not recovered their sense of smell and taste also suffered from nasal congestion, runny nose, and 32.62% (3 210/9 840) suffered from dry mouth and sore throat. The improvement of olfactory and taste functions was correlated with the persistence of accompanying symptoms(χ2=10.873, P=0.001). The average score of olfactory and taste VAS scale was 8.41 and 8.51 respectively before SARS-CoV-2 infection, but decreased to3.69 and 4.29 respectively after SARS-CoV-2 infection, and recovered to 5.83and 6.55 respectively at the time of the survey. The median duration of olfactory and gustatory dysfunctions was 15 days and 12 days, respectively, with 0.5% (121/24 096) of patients experiencing these dysfunctions for more than 28 days. The overall self-reported improvement rate of smell and taste dysfunctions was 59.16% (14 256/24 096). Gender(OR=0.893, 95%CI: 0.839-0.951), SARS-CoV-2 vaccination status (OR=1.334, 95%CI: 1.164-1.530), history of head and facial trauma(OR=1.180, 95%CI: 1.036-1.344, P=0.013), nose (OR=1.104, 95%CI: 1.042-1.171, P=0.001) and oral (OR=1.162, 95%CI: 1.096-1.233) health status, smoking history(OR=0.765, 95%CI: 0.709-0.825), and the persistence of accompanying symptoms (OR=0.359, 95%CI: 0.332-0.388) were correlated with the recovery of olfactory and taste dysfunctions related to SARS-CoV-2 (above P<0.001 except for the indicated values). Conclusion: The incidence of olfactory and taste dysfunctions related to infection with the SARS-CoV-2 Omicron strain is high in mainland China, with females and young people more likely to develop these dysfunctions. Active and effective intervention measures may be required for cases that persist for a long time. The recovery of olfactory and taste functions is influenced by several factors, including gender, SARS-CoV-2 vaccination status, history of head and facial trauma, nasal and oral health status, smoking history, and persistence of accompanying symptoms.

[Clinical analysis of 5 cases of dural arteriovenous fistulas complained of pulsatile tinnitus].

Objective: The clinical characteristics of dural arteriovenous fistula with pulsatile tinnitus were analyzed to deepen the understanding of the disease. Methods: The clinical data of five patients complained of pulsatile tinnitus and diagnosed dural arteriovenous fistula in Henan People's Hospital from May 2013 to June 2018 were retrospectively analyzed, including 3 males and 2 females, aged 27-65 years. Results: The main clinical symptoms of the five patients were continuous pulsatile tinnitus, accompanied/not accompanied by headache, memory decline, etc., with a course of three months to 20 years. They were diagnosed as dural arteriovenous fistula by digital subtraction angiography, and three cases of tinnitus disappeared and two cases of tinnitus were relieved after embolization. Conclusions: The dural arteriovenous fistula is a rare and complicated disease. When the patient complain of the pulsatile tinnitus, the related etiology should be considered and managed properly.

[Analyses of diagnosis and treatment of foreign body aspiration in children with tracheobronchial variations].

Objective: To investigate the key issues in the diagnosis and treatment of foreign body aspiration in children with tracheobronchial variations. Methods: A retrospective study was performed for 11 pediatric patients who were treated in Department of Otorhinolaryngology and Head and Neck Surgery, Henan Province People's Hospital after a diagnosis of foreign body aspiration with tracheobronchial variations between January 2015 and December 2017. There were 7 males and 4 females among the 11 cases of foreign body aspiration with tracheobronchial variations, ranging between 9 months and 11 years of age. Results: Among 11 cases, the types of variationswere tracheal bronchus in 9 cases, bridging bronchus in 1 case and simple tracheal stenosis in 1 case. All of the pediatric patients were under general anesthesia, and the foreign bodies were removed by bronchoscopy successfully with no significant complications. Conclusions: The possibility of tracheobronchial variations should be considered in children with recurrent wheezing and poor efficacy of regular treatment before foreign body aspiration. Removal of foreign body via rigid bronchoscope under general anesthesia is a safe and effective treatment. These children are needed to combine the situation oftracheobronchial variations and the location of foreign bodies to guide the operation, and strengthened the perioperative treatment.

[Diagnosis and therapy strategy of acute invasive fungal rhino-sinisitis].

Summary Acute invasive fungal rhino-sinisitis(AIFRS) is a kind of acute fungus infectious disease.It ofen deteriorates rapidly and abruptly,which occurs in the nose and sinuses with somepeople who have low immunological function.This paper reviewed the progress about the acute invasive fungal rhino-sinisitis's clinical characteristics,diagnosis,treatment and prognosis to improve the level of early diagnosis and reduce the mortality.

[Endoscopic sinus surgery for the treatment of invasive fungal sinusitis].

Objective:To explore the early diagnosis, the treatment and theprognosis of invasive fungal rhinosinusitis.Method:By summarizing the clinical data of 18 patients, CT and MRI images, pathological diagnosis and follow-up results to analysis the early diagnosis and the treatment.Result:All 5 patients with invasive fungal sinusitis were infected with mucor, 3 of whom died of intracranial complications. Among 13 patients with chronic invasive fungal rhinosinusitis, 9 were aspergillus, 3 were mucor, and 1 was negative. There were 9 cases of diabetes, 1 cases of ankylosing spondylitis, 3 cases of hypoproteinemia, 1 cases of organ transplantation, and 1 cases of leukemia. There were 3 cases of death who unenforced the operation, 15 patients received enlarged endoscopic surgery, postoperative antifungal therapy. Followed up 1-3 years, relapse in 3 cases, 1 case of death.Conclusion:The diagnosis of FRS needs to be combined with clinical manifestations, imaging features and pathological findings. The treatment requires surgery to completely remove diseased tissue (enlarged sinus open surgery) combined with antifungal use in sufficient quantities.

Protective role of curcumin on renal ischemia reperfusion injury via attenuating the inflammatory mediators and Caspase-3.

Renal ischemia/reperfusion (I/R) damage may arise due to nephron sparing surgery in patient with a solitary kidney of restricted renal parenchymas. Apoptosis, inflammation and oxidative stress play a significant role in the expansion of renal dysfunction following renal I/R. The aim of the current investigation was to particularize the potential effect of curcumin against hypoxia induced renal injury. The albino Wistar rats divided into groups and each group contains six rats. They groups are normal control; disease control; curcumin (5 mg/kg per day) and another group orally treated with curcumin (10 mg/kg per day) for two weeks before induction of renal I/R. The renal and serum samples were collected and used for the biochemical estimation. The renal tissue was further used for the histopathological estimation. The result of the current investigation demonstrated that the curcumin significantly (P<0.01) attenuated I/R induced renal injury in a dose-dependent way. It also causes significant (P<0.01) reduction in the serum creatinine, blood urea nitrogen level and also suppressed the kidney injury molecules-1. Additionally, it also causes significant inhibition of the malonaldehyde, caspase-3, myeloperoxide, lactose dehydrogenase and interferon-gamma together with enhanced interlukin-10 content.

[Voice acoustic study of plasma radiofrequency ablation for the treatment of laryngeal premalignant lesions].

Objective:To study the voice function effect of low temperature plasma radiofrequency ablation in the treatment of patients with laryngeal premalignant lesions. Method:Fifty cases of laryngeal premalignant lesions were treated with low temperature plasma radiofrequency ablation. All of the patients were examined by electronic laryngoscopy and acoustic analysis(F0，Jitter，Shimmer，NNE，HNR) in 2 weeks,1 month,3 months after surgery. Voice acoustic results were compared with a control group of 50 normal adults for the further analysis. Result:Fifty patients with laryngeal premalignant lesions were treated by low temperature plasma radiofrequency ablation.The result showed that 47 patients(94%)were successfully decannulated without serious complications, such as dyspnea, aphonia and anterior glottic stenosis. Acoustic analysis showed that F0,Jitter,Shimmer and NNE were significantly different from normal 2 weeks after surgery（P<0.01）.Voice function recovered weakly 1 month after operation（P<0.05）.There were no significant differences in the vocal parameters between plasma radiofrequency ablation group and control group 3 months after surgery(P>0.05). Conclusion:Radiofrequency coblation was a safe,minimally invasive and effective surgical method and can be widely used to treat laryngeal premalignant lesions．.

Comparison of dual-source parallel radio frequency transmission liver MRI at 3.0 T with conventional MRI.

AIM: Aim of the present study was to investigate the role of dual-source parallel Radio frequency (RF) and single-source excitation in liver imaging at 3.0 T MR. METHODS: This study was a retrospective analysis. One hundred and seven subjects underwent a 3.0 T TX MR scanning including axial spectrally selective attenuated inversion recovery (SPAIR) T2WI, axial DWI and coronal balanced-fast field echo (Balanced FFE). Each sequence was carried out with both single-source and dual-source RF excitation. Student's t test was used to compare whether there was difference between single-source and dual-source RF excitation in the image uniformity, single-to-noise ratio (SNR) and contrast-to-noise ratio (CNR). Wilcoxon signed rank test was used to determine whether there was difference between conventional and parallel transmission in the score of image quality. Reader agreement was assessed using the Cohen's Kappa test. RESULTS: For the image uniformity, there was significant difference between single-source and dual-source excitation (418.40±66.75 for single-source vs. 416.26±50.61 for dual-source, t=2.524, P<0.05). There also existed significant difference between single-source and dual-source excitation in SNR and CNR, respectively. The SNR and CNR of parallel transmission (22.03±12.16 and 18.33±10.01, respectively) were both higher than those of single transmission (20.36±11.21 and 15.22±8.95, respectively) (t=-2.630, P<0.05 for SNR and t=-4.238, P<0.05 for CNR). Image quality comparisons revealed significantly better results with dual-source than single-source RF excitation at SPAIR T2WI (1.4±0.42 vs. 1.81±0.27), DWI (1.08±0.46 vs. 1.63±0.36) and balanced FFE sequence (0.95±0.45 vs. 1.65±0.37, Z=-5.894, -5.801 and -6.985, respectively, P<0.01). In the comparison of image quality, the agreement between the two readers was very good (Kappa>0.8, P<0.05). CONCLUSION: Dual-source parallel RF excitation MR imaging in liver enables reducing dielectric shading, improving homogeneity of the RF magnetic induction field, and increasing SNR and CNR at 3.0 T.

The signaling network of tumor invasion.

The ability of a cell to invade its surroundings is an important hallmark of malignant tumors and results from aberrant cell signaling mechanisms. The signal transduction that leads to tumor invasion can be broken down into major pathways. Even though the pathway systems are distinct in themselves, none of these pathways operate independently when it comes to transmitting signals that culminate in an invasive phenotype. That is, the malignant change in one receptor not only leads to malignant changes directly downstream but can also affect the molecules of many other pathways. Three major pathway systems involved in tumor invasion are discussed in this review: the integrin system, the insulin-like growth factor system, and the Rho family GTPases. Here we see that although the individual signaling systems can each contribute to invasion, each system is networked to others and should not be considered isolated. Each system is first reviewed as independent contributors to an invasive phenotype and then discussed in the context of interacting pathways that collectively result in tumor invasion.

Methanethiosulfonate-modification alters local anesthetic block in rNav1.4 cysteine-substituted mutants S1276C and L1280C.

We previously showed that lysine substitutions at two residues in segment 6 of domain 3 in voltage-gated Na(+) channel rNav1.4 (S1276K, L1280K) reduced steady-state inactivated local anesthetic block. Here we studied cysteine substitutions at the same residues (S1276C, L1280C). We used whole-cell recordings to determine local anesthetic block (100 microM bupivacaine) before and after cysteine modification with 1.5 mM 2-aminoethyl methanethiosulfonate (MTSEA). Compared with rNav1.4, steady-state resting bupivacaine block at -180 mV was increased in S1276C, while inactivated block at -50 mV was not different in the mutants. After application of MTSEA at -160 mV, rNav1.4 showed enhanced bupivacaine block and a negative shift in V(1/2) of the bupivacaine affinity curve, while L1280C and S1276C showed a decrease in inactivated bupivacaine block after MTSEA. Application of MTSEA at 0 mV produced similar results in rNav1.4 and L1280C, but an opposite effect in S1276C, i.e., enhancement of bupivacaine block, with a large negative shift in V(1/2) of the bupivacaine affinity curve similar to that found in rNav1.4. We conclude that 1) MTSEA modification of 1276C or 1280C decreases inactivated bupivacaine block similar to that found in L1280K and S1276K, 2) residue 1276C is only accessible to MTS-modification in the resting state, and 3) MTSEA may modify a native cysteine in rNav1.4 that produces an allosteric, indirect effect on bupivacaine affinity.

Residue-specific effects on slow inactivation at V787 in D2-S6 of Na(v)1.4 sodium channels.

Slow inactivation in voltage-gated sodium channels (NaChs) occurs in response to depolarizations of seconds to minutes and is thought to play an important role in regulating membrane excitability and action potential firing patterns. However, the molecular mechanisms of slow inactivation are not well understood. To test the hypothesis that transmembrane segment 6 of domain 2 (D2-S6) plays a role in NaCh slow inactivation, we substituted different amino acids at position V787 (valine) in D2-S6 of rat skeletal muscle NaCh mu(1) (Na(v)1.4). Whole-cell recordings from transiently expressed NaChs in HEK cells were used to study and compare slow inactivation phenotypes between mutants and wild type. V787K (lysine substitution) showed a marked enhancement of slow inactivation. V787K enters the slow-inactivated state approximately 100x faster than wild type (tau(1) approximately 30 ms vs. approximately 3 s), and occurs at much more hyperpolarized potentials than wild type (V(1/2) of s(infinity) curve approximately -130 mV vs. approximately -75 mV). V787C (cysteine substitution) showed a resistance to slow inactivation, i.e., opposite to that of V787K. Entry into the slow inactivation state in V787C was slower (tau(1) approximately 5 s), less complete, and less voltage-dependent (V(1/2) of s(infinity) curve approximately -50 mV) than in wild type. Application of the cysteine modification agent methanethiosulfonate ethylammonium (MTSEA) to V787C demonstrated that the 787 position undergoes a relative change in molecular conformation that is associated with the slow inactivation state. Our results suggest that the V787 position in Na(v)1.4 plays an important role in slow inactivation gating and that molecular rearrangement occurs at or near residue V787 in D2-S6 during NaCh slow inactivation.

A common local anesthetic receptor for benzocaine and etidocaine in voltage-gated mu1 Na+ channels.

According to Hille's modulated receptor hypothesis, benzocaine shares a common receptor with all other local anesthetics (LAs) in the voltage-gated Na+ channel. We tested this single receptor hypothesis using mutant muscle Na+ channels of mu1-I1575A, F1579A, and N1584A transiently expressed in Hek-293t cells. Both benzocaine and etidocaine are more effective at blocking mu1-N1584A current than the wild-type current, while they are less potent at blocking mu1-F1579A current. Such concurrent changes of both benzocaine and etidocaine potency towards F1579A and N1584A mutants suggest that they share a common LA receptor. Consistent with results found in studies of native Na+ channels, permanently charged QX-314 at 1 mM is not effective at blocking wild-type, F1579A, and N1584A current via external application. In contrast, QX-314 is relatively potent at blocking I1575A current when applied externally. This increased potency of external QX-314 against the mu1-I1575A mutant has been reported previously in a study of the brain counterpart. Mutant I1575A also appears to be highly sensitive to the external divalent cation Cd2+, probably because of the presence of cysteine residues near the mu1-I1575 position in the IV-S6 segment. To our surprise, neutral benzocaine becomes more effective at blocking mu1-I1575A current than the wild-type current, whereas the opposite is found for etidocaine. We hypothesize that an increase in accessibility of external QX-314 to the mu1-I1575A mutant is accompanied by a reduction of binding towards the charged amine component.

4-Aminopyridine binding and slow inactivation are mutually exclusive in rat Kv1.1 and Shaker potassium channels.

In the present study we have used two-electrode voltage-clamping of Xenopus oocytes expressing either Kv1.1 or Shaker B (ShB) delta 6-46 K+ channels to examine the effects of 4-aminopyridine (4-AP) on the process of slow inactivation. Neither of these channels exhibits fast inactivation. Channel activation was required for block by 4-AP in both channel types. In the absence of drug, inactivation of Kv1.1 and ShB delta 6-46 channels at 0 mV was biexponential [tau fast = 7.8 +/- 0.3 sec, tau slow = 33.9 +/- 0.9 sec, and Aslow/(Afast + Aslow) = 0.79 +/- 0.02 (n = 10) for Kv1.1 and tau fast = 3.5 +/- 0.4 sec, tau slow = 13.1 +/- 1.8 sec, and Aslow/(Afast + Aslow) = 0.35 +/- 0.06 (n = 3) for ShB delta 6-46]. In the presence of 4-AP, the rates of inactivation of Kv1.1 and ShB delta 6-46 were markedly slowed, resulting in a crossover phenomenon where, in the presence of drug, the outward current was smaller than control at the beginning of the depolarizing pulse but crossed over during the pulse to become larger than the control. The most obvious change induced by 0.2 mM 4-AP was a 2-fold slowing of the slow phase of inactivation [tau fast = 3.9 +/- 1.1 sec, tau slow = 67.1 +/- 3.6 sec, and Aslow/(Afast + Aslow) = 0.85 +/- 0.04 (n = 4) for Kv1.1 and tau fast = 3.5 +/- 0.4 sec, tau slow = 23.7 +/- 2.6 sec, and Aslow/(Afast + Aslow) = 0.75 +/- 0.02 (n = 3) for ShB delta 6-46, in the presence of 0.2 mM 4-AP]. In addition, there was a significant increase in the contribution of the slower phase of inactivation of ShB delta 6-46 channels in the presence of 4-AP. The slowed inactivation in the presence of 4-AP was accompanied by removal of 4-AP block. These results are consistent with the processes of 4-AP block and slow inactivation of Kv1.1 and ShB delta 6-46 channels being mutually exclusive.

Identification of RBK1 potassium channels in C6 astrocytoma cells.

Ionic currents in C6 astrocytoma cells were studied using the patch clamp technique under the whole cell configuration. A delayed rectifier K+ current with an amplitude of approximately 1 nA at +50 mV was observed in 86% (92/107) of the cells examined. This K+ current resembled the delayed rectifier present in type-1 and type-2 astrocytes in vitro and could be inhibited by a variety of K+ channel blockers, including TEA (IC50:0.5 mM), 4-aminopyridine (IC50:0.2 mM), MCD peptide (IC50:52 nM), dendrotoxin I (IC50:9 nM), and charybdotoxin (74% inhibition at 50 nM). Northern blot analysis, cloning of cDNA and subsequent sequencing showed that the C6 cell delayed rectifier K+ channel is equivalent to the RBK1 K+ channel derived from a rat brain cDNA library. The level of RBK1 transcripts in C6 cells was comparable to that reported in rat brain. The C6 delayed rectifier K+ channel is probably a homomeric RBK1 K+ channel judging from its pharmacological properties which are similar to the RBK1 channel expressed in Xenopus oocytes. Some C6 cells also expressed a transiently activated outward K+ current (IA). This current was found in less than 50% of the cells and in general contributed no more than 8% of the total outward current. No voltage-dependent inward Na+ or Ca2+ currents or inwardly rectifying K+ currents were observed in over 100 C6 cells examined. The present results show that the dominant voltage gated ionic current in C6 cells is the RBK1 delayed rectifier K+ channel.(ABSTRACT TRUNCATED AT 250 WORDS)

An integrated view of the molecular toxinology of sodium channel gating in excitable cells.

The neurotoxins that modify Na channels have actions that are characterized by different degrees of specificity (Table 2). These specificities can be correlated with their chemical properties. For example, guanidinium toxins, which are small charged ligands, appear only to "block" Na channels by binding to a site on the external surface. Peptide toxins, which are also positively charged and relatively small, also act from the external solution to modify channel activation and inactivation processes but do not alter ion selectivity. The lipophilic toxins, hydrophobic, neutral drugs, act from either side of the membrane and modify all the functions of Na channels. From such differences, and from the independence of toxin binding as well as toxin action, separate binding sites for these agents have been classified (Catterall 1980). Recent findings reviewed here suggest that all these toxins share certain features: They differentiate between various states of the channel. Effects of lipophilic activators, polypeptide toxins, and, indeed, even STX and TTX are enhanced or reversed in fractions of seconds under voltage clamp by patterns of membrane potential that selectively populate the channel open state, or the slow or fast inactivated states. Other assays--such as the binding of radiolabeled ligands or the changes of steady-state Na flux that require seconds to minutes of toxin-channel interaction--reveal interactions of the toxins with states of the channel not detected in the usual voltage-clamp analysis. Pharmacological probes may thus reveal channel states or transitions previously unrecognized. The bound toxins appear to interact with one another. The well-documented synergism at equilibrium of alpha-toxins with lipophilic activators provided a model for allosteric interactions between two separate binding sites (Catterall 1979, 1980). The other toxin interactions are more ephemeral and are characterized by kinetic variations that reflect the availability of reactive channel states. For example, the appearance of beta-toxin induced modifications of Na currents is accelerated in the presence of alpha-toxin (Wang & Strichartz 1983), whereas the modifications of inactivation by alpha-toxins are prevented by concurrent incubation with tetrodotoxin, although such modifications, once effected, are not reversed by the subsequent addition of TTX. Modifications of gating by lipophilic toxins confer a selective voltage-dependence on STX and TTX inhibition of open channels that is not observed in drug-free channels.(ABSTRACT TRUNCATED AT 400 WORDS)

Irreversible modification of sodium channel inactivation in toad myelinated nerve fibres by the oxidant chloramine-T.

The effects of externally applied chloramine-T on the excitability of single toad myelinated nerve fibres were studied. Chloramine-T is a mild oxidant which reacts specifically with the cysteine and methionine residues of proteins. Chloramine-T prolongs the action potential of a single myelinated fibre by more than 1000-fold. This effect is concentration- and time-dependent; higher concentrations and longer incubation times increase prolongation. Under voltage-clamp conditions, sodium channel inactivation is markedly inhibited by chloramine-T while sodium channel activation remains normal. Prolonged depolarization of the membrane leads to a maintained sodium current. The maintained sodium currents show activation kinetics, dependence on membrane potential, and reversal potentials which are similar to those of normal, inactivating sodium currents in untreated fibres. Both the maintained and the peak sodium currents are equally inhibited by tetrodotoxin. After partial removal of sodium inactivation by brief exposures to chloramine-T, the voltage dependence of the steady-state sodium current inactivation (h infinity) is shifted in the depolarized direction by about 20 mV, even after correction for the non-inactivating component contributed by the maintained current. The phenomena described here imply that cysteine or methionine residues are critical for the sodium channel inactivation processes. The two different modifications of inactivation, its removal shown by the maintained current, and the shift in the voltage-dependence of the remaining inactivatable channels, reveal that at least two separate residues are modified by chloramine-T.

Ligand responses of alpha-bungarotoxin binding sites from skeletal muscle and optic lobe of the chick.

Binding properties of detergent-solubilized receptors for alpha-bungarotoxin from skeletal muscle of the 13th day chick embryo and from optic lobe of the hatching chick were compared. It was found that both types of receptor are nicotinic, although they differ in their affinities for individual ligands and in the rank order of ligands. In contrast to the muscle receptor, the neuronal receptor binds the toxin in a reversible fashion (KD = 2.1 X 10(-10) M at 23 degrees C). Small ligands inhibit brain equilibrium procedures. Toxin and ligands compete for a single type of noninteracting site, and the ratio of toxin binding sites to ligand-binding sites is unity. The inhibitory potency of ligands parallels their ability, at higher concentrations, to accelerate receptor . toxin by interaction with the same site on the receptor derived from the optic lobe.