Monetary reinforcement for self-monitoring of blood glucose among young people with type 1 diabetes: evaluating effects on psychosocial functioning.

AIMS: To explore the auxiliary psychosocial effects of a monetary reinforcement intervention targeting self-monitoring of blood glucose among young people with Type 1 diabetes. METHODS: Sixty young people with Type 1 diabetes, HbA1c concentrations between 58 and 119 mmol/mol (7.5-13.0%), and average self-monitoring of blood glucose <4 times per day were randomized to either enhanced usual care or a 24-week intervention of monetary rewards for self-monitoring of blood glucose and associated behaviours (e.g. uploading glucose meters). Data were collected from the young people and their parents at baseline, during the intervention (6, 12 and 24 weeks) and after the intervention (36 weeks). RESULTS: Linear mixed models were used to evaluate the intervention effects on psychosocial outcomes, adjusting for corresponding baseline levels and potential moderation by baseline level. The intervention reduced diabetes distress at week 6 among young people who had average and high baseline distress. It also reduced diabetes distress at weeks 12 and 24 among those with low baseline distress. The intervention also reduced young person-reported diabetes-related family conflict and diabetes-related interference among those with high baseline scores in these areas; however, the intervention worsened young person-reported diabetes interference among those with low baseline interference. Effects were medium-sized and time-limited. CONCLUSIONS: Findings indicate predominantly positive impacts of monetary reinforcement interventions on psychosocial outcomes, although effects varied by outcome and time point. Whereas early improvements in diabetes distress were observed for all who received the intervention, improvements in other areas varied according to the level of psychosocial challenge at baseline. Incorporating psychosocial interventions may bolster and maintain effects over time.

Evaluación de la función muscular del cuádriceps en pacientes con EPOC modera-severa / Evaluation of quadricep muscle function in patients with moderate-severe COPD

Objetivo: el objetivo del estudio fue evaluar la función muscular periférica de pacientes con EPOC moderadasevera, mediante la medición de la fuerza muscular isométrica e isotónica del cuádriceps y la masa muscular mediante ecografía. Método: fueron incluidos pacientes con EPOC moderada-severa estables, remitidos a Rehabilitación Respiratoria. En la extremidad dominante, se midió la fuerza isométrica (dinamómetro hidráulico), test 1RM y se realizó una ecografía para obtener el área transversal y dimensiones de diversas secciones musculares. Resultados: participaron 34 pacientes con EPOC estable: GOLD 2 (n = 11), GOLD 3 (n = 12) y GOLD 4 (n = 11) Los GOLD 4 tenían un IMC P50 (P25 - P75) 25,3 (22,5 - 28,8), significativamente menor que los GOLD 3: 32,0 (27,5 - 34,0); p = 0,025. Se evidenció debilidad del cuádriceps (1RM/peso <0,60 1RM/IMC <120%), de forma global: 0,33 (0,22 - 0,41) y 93% (61 - 112) respectivamente, y en cada grupo, sin diferencias significativas entre ellos. Tampoco hubo diferencias significativas entre los grupos en las mediciones de ecografía muscular. La fuerza isotónica (1RM) se correlacionó con el grosor del cuádriceps QT (r = 0,529; p = 0,003) y el grosor del músculo vasto intermedio Q1(r = 0,514; p = 0,004) La fuerza isométrica se correlacionó con el QT (0,621; p <0,001), Q1 (0,441; p = 0,009) y el área transversal AQ (r = 0,587; p <0,001) Para cada grupo, el QT y la fuerza isométrica se correlacionaron significativamente. Conclusión: en nuestra serie de pacientes se demuestra la existencia de debilidad muscular del cuádriceps, independientemente del grado de severidad de la enfermedad y en estrecha relación con la masa muscular de dicho músculo. Palabras clave: disfunción muscular, fuerza isotónica, 1RM, fuerza isométrica, ecografía muscular

Objective: The objective of this study was to evaluate peripheral muscle function in patients with moderate-severe COPD by measuring isometric and isotonic muscular strength of the quadriceps and muscle mass through ultrasound. Method: This study included stable patients with moderate-severe COPD who were referred to pulmonary rehabilitation. In the dominant extremity, isometric strength (hydraulic dynamometer) and the 1RM test were measured and an ultrasound was done to determine the transversal area and dimensions of different sections of muscle. Results: 34 stable patients with COPD participated: GOLD 2 (n = 11), GOLD 3 (n = 12) and GOLD 4 (n = 11). GOLD 4 patients had a BMI P50 (P25 - P75) 25.3 (22.5 - 28.8), which was significantly lower than GOLD 3 patients: 32.0 (27.5 - 34.0); p = 0.025. Weakness in the quadriceps was observed (1 RM/weight <0.60; 1 RM/BMI <120%) overall: 0.33 (0.22 - 0.41) and 93% (61 - 112), respectively, and in each group, without significant differences between groups. There were also no significant differences between groups for ultrasound muscle measurements. Isotonic strength (1 RM) correlated to quadricep thickness QT (r = 0.529; p = 0.003) and vastus intermedius muscle thickness Q1(r = 0.514; p = 0.004). Isometric strength correlated to QT (0.621; p <0.001), Q1 (0.441; p = 0.009) and transversal area AQ (r = 0.587; p <0.001). QT and isometric strength were significantly correlated in each group. Conclusion: In our study, patients showed muscular weakness in the quadriceps, regardless of the degree of disease severity and this weakness was closely related to the mass of said muscle

Assessing patient-reported outcomes for automated insulin delivery systems: the psychometric properties of the INSPIRE measures.

AIM: Participants in clinical trials assessing automated insulin delivery systems report perceived benefits and burdens that reflect their experiences and may predict their likelihood of uptake and continued use of this novel technology. Despite the importance of understanding their perspectives, there are no available validated and reliable measures assessing the psychosocial aspects of automated insulin delivery systems. The present study assesses the initial psychometric properties of the INSPIRE measures, which were developed for youth and adults with Type 1 diabetes, as well as parents and partners. METHODS: Data from 292 youth, 159 adults, 150 parents of youth and 149 partners of individuals recruited from the Type 1 Diabetes Exchange Registry were analysed. Participants completed INSPIRE questionnaires and measures of quality of life, fear of hypoglycaemia, diabetes distress, glucose monitoring satisfaction. Exploratory factor analysis assessed factor structures. Associations between INSPIRE scores and other measures, HbA1c , and technology use assessed concurrent and discriminant validity. RESULTS: Youth, adult, parent and partner measures assess positive expectancies of automated insulin delivery systems. Measures range from 17 to 22 items and are reliable (α = 0.95-0.97). Youth, adult and parent measures are unidimensional; the partner measure has a two-factor structure (perceptions of impact on partners versus the person with diabetes). Measures showed concurrent and discriminant validity. CONCLUSIONS: INSPIRE measures assessing the positive expectancies of automated insulin delivery systems for youth, adults, parents and partners have meaningful factor structures and are internally consistent. The developmentally sensitive INSPIRE measures offer added value as clinical trials test newer systems, systems become commercially available and clinicians initiate using these systems.

Maternal hypothyroxinemia impairs spatial learning and synaptic nature and function in the offspring.

Neurological deficits in the offspring caused by human maternal hypothyroxinemia are thought to be irreversible. To understand the mechanism responsible for these neurological alterations, we induced maternal hypothyroxinemia in pregnant rats. Behavior and synapse function were evaluated in the offspring of thyroid hormone-deficient rats. Our data indicate that, when compared with controls, hypothyroxinemic mothers bear litters that, in adulthood, show prolonged latencies during the learning process in the water maze test. Impaired learning capacity caused by hypothyroxinemia was consistent with cellular and molecular alterations, including: 1) lack of increase of phosphorylated c-fos on the second day of the water maze test; 2) impaired induction of long-term potentiation in response to theta-burst stimulation to the Schaffer collateral pathway in the area 1 of the hippocampus Ammon's horn stratum radiatum, despite normal responses for input/output experiments; 3) increase of postsynaptic density protein 95 (PSD-95), N-methyl-D-aspartic acid receptor subunit 1, and tyrosine receptor kinase B levels in brain extracts; and 4) significant increase of PSD-95 at the PSDs and failure of this molecule to colocalize with N-methyl-D-aspartic acid receptor subunit 1, as it was shown by control rats. Our findings suggest that maternal hypothyroxinemia is a harmful condition for the offspring that can affect key molecular components for synaptic function and spatial learning.

Prevalencia de displasia de vesícula biliar / Frequency of gallbladder dysplasia in gallbladders excised during cholecystectomy

Introducción: El cancer de vesícula biliar es una enfermedad muy frecuente en la actualidad, sobre todo en Chile, la India y Japón. La displasia de vesícula biliar es considerada como una lesión que precede la aparición de carcinoma vesicular. Objetivos: El objetivo de este estudio es determinar la prevalencia de la displasia de vesícula biliar en nuestro centro hospitalario y conocer sus características histológicas y clínicas. Material y Método: Los datos obtenidos de 1.237 informes de biopsias de colecistectomías realizadas en el hospital durante el año 2003 fueron procesados y analizados. Resultados: La prevalencia de la displasia de vesícula biliar fue de 2,5%. Del total de displasias (31 casos), 12 pertenecen a grado I (38,7%), 14 a grado II (45,16%) y 5 a grado lll-CIS ( carcinoma in situ 16%). La edad promedio en que se detectó la displasia de vesícula biliar fue de 54.7 años, siendo predominante en el sexo femenino con un 74,2%. Discusión: La displasia de vesícula biliar es una patología prevalente que sólo es posible diagnosticar mediante la histología realizada a los pacientes sometidos a colecistectomías.

Introduction: Gallbladder dysplasia is considered a premalignant stage, preceding the appearance of carcinoma. Aim: To assess the prevalence of gallbladder dysplasia in gallbladder biopsies. Material and methods: Review of pathology reports of 1237 gallbladders obtained during cholecystectomies, during 2003. Results: Thirty one reports informed the presence of dysplasia (2.5%). Of these, 12 were in stage 1 (39%), 14 were in stage 2 (45%) and 5 in stage 3-ISC (in-situ carcinoma, 16%). The mean age of patients with gallbladder dysplasia was 54 years. Discussion: Gallbladder dysplasia is common. The pathological study of the excised gallbladders is the only way to make the diagnosis.

Estado de la cesárea en Chile: riesgos y beneficios asociados a esta intervención / State of the cesarean in Chile: risks and benefits associated to this intervention

Chile has one of the highest cesarean rates in the World. Many factors contribute to increase its incidence. Medical literature shows us that even though there are differences in neonatal and maternal outcomes among patients that undergo cesarean or vaginal delivery; evidence, besides the contrast in costs, is not concluding. Disparities between the private sector and the National System of Health Services (SNSS) are unquestionable. The application of regulatory rules and the individualized registry of actions, as well as a system of medical auditory could help lower significantly the numbers of cesareans. The actual state of cesarean in the public sector and some private health institutions is shown. The elevated rate of cesareans does not assure good quality obstetric care. Private sector interventions could be causing unsuitable handling of this situation, which is why they should give detailed information of the factors implied in their obstetric care and perinatal outcomes obtained in order to evaluate the impact of their interventions.

Cómo realizar una evaluación de deglución completa, eficaz y en corto tiempo / How to make a complete, efficient and short-time evaluation of deglution

El trastorno de deglución es una patología que va en aumento en los pacientes hospitalizados. El estudio y manejo de esta condición tiene muchas alternativas según la bibliografía. Analizamos las interconsultas para evaluación de deglución enviadas a nuestro servicio entre el 1 de enero al 31 de diciembre de 2004. Se confeccionó un protocolo con los antecedentes y el examen realizado y se clasificó a los pacientes según la severidad del trastorno observado ingresando así a un algoritmo diseñado para continuar su terapia y seguimiento. Este trabajo pudo comprobar la alta incidencia del trastorno de deglución en pacientes hospitalizados; que correspondió al 20 por ciento del total de interconsultas del Servicio. Las dos causas más frecuentes para este trastorno fueron: accidente vascular en un 56 por ciento e intubación prolongada en un 58 por ciento; algunos pacientes presentaban ambos diagnósticos. Los resultados mostraron que los factores que más se relacionaban con un trastorno de deglución severo eran: sexo masculino, limpieza oral incompleta, manejo anormal de la saliva, movilidad palatina anormal, saliva moviéndose libremente en glotis, disminución de la sensibilidad en la glotis, restos en seno piriforme y ahogo al comer. Se propone un protocolo de evaluación de deglución para este tipo de pacientes acorde a nuestra experiencia como Servicio de Otorrinolaringología.

Cirugía bariátrica y embarazo / Bariatric surgery and pregnancy

El número de pacientes sometidos a cirugía bariátrica ha aumentado rápidamente en el mundo. Esta revisión pretende describir la literatura publicada relativa a las deficiencias nutricionales posteriores a la cirugía bariátrica y su importancia en el embarazo.

Anticoagulación y embarazo / Anticoagulation and pregnancy

Se comentan los aspectos clínicos del tratamiento anticoagulante en la paciente embarazada.

Análisis clínico y economico de la histerectomía abdominal versus la histerectomía vaginal en el hospital clínico de la universidad de chile: revision de 2.338 casos

Antecedentes: La histerectomía es una intervención quirúrgica frecuente y de alto costo. Después de la operación cesárea, es el segundo procedimiento quirúrgico más frecuente en ginecología. Objetivos: Evaluar la relación costo/efectividad de la histerectomía vaginal versus la histerectomía abdominal. Método: Estudio retrospectivo observacional, en 2.338 pacientes sometidas a histerectomía por patología benigna en el Servicio de Ginecología del Hospital Clínico de la Universidad de Chile, en el período comprendido entre enero de 1997 a diciembre de 2005. Se analizaron variables clínicas y de costo entre las dos vías de abordaje. Resultados: La edad de las pacientes fluctuó entre 27 y 86 años. De las 2.338 histerectomías, la vía vaginal correspondió al 36,9 por ciento y la abdominal en el 63,1 por ciento; con una tasa de complicaciones de 29,8/100 mujeres operadas vaginalmente y de 42,8/100 mujeres operadas abdominalmente. Conclusión: Este estudio sugiere que el abordaje vaginal se asoció a tiempos operatorios más cortos, menor número de complicaciones y a costos más bajos que la vía abdominal.

Background: After cesarean delivery, hysterectomy it is the second most frequently performed major surgical procedure. Objective: To study de relation cost/effectivity between vaginal and abdominal hysterectomy. Method: Retrospective and observational study in 2338 hysterectomy, performed between January 1997 and December 2005. Clinical and cost variables were analysed between both surgical routes. Results: The study included 2338 patients aged 27 to 86 years in whom hysterectomy was performed for benign gynaecologic disorders. Of 2338 hysterectomies, 36.9 percent were performed vaginally and an abdominal approach was required in 63.1 percent. The overall complication rate was 29.8 per 100 women for vaginal hysterectomy and 42.8 per 100 women for abdominal hysterectomy. Conclusion: This study suggests that vaginal route presents some advantages in comparison to abdominal hysterectomy that include less expensive, fewer complications, shorter operating times and shorter stays.

Quistes vaginales

Se reportan dos casos de quistes vaginales: se analiza el cuadro clínico y su dificultad diagnóstica.

We report two cases of vaginal cysts: clinical presentation and diagnostic difficulties are analysed.

Evaluación de calidad de asistencia en obstetricia, periodo 2004-2005 en el Hospital Clínico de la Universidad de Chile / Evaluation of quality of attendance in obstetrics, period 2004-2005 in the Hospital Clínico de la Universidad de Chile

Existen numerosos indicadores de calidad de asistencia utilizados por organizaciones públicas, privadas y sin fines de lucro, que tienen por finalidad mejorar mejorar la práctica asistencial de maternidades. El objetivo de este trabajo fue comparar los estandares de dichos indicadores con los obtenidos en el Servicio de Maternidad del Hospital Clínico de la Universidad de Chile en el año 2004 y 2005.

Many public and private organizations use different obstetrical care quality indicators to improve medical care practice in maternity wards. The purpose of this study was to compare the available standards for those indicators, with the results obtained in the Obstetrics Service of the University of Chile’s Clinical Hospital, for the 2004-2005 period.

Perspectivas actuales de la obstetricia / Present perspectives of obstetrics

La probabilidad de que una pareja tenga un hijo con alguna alteración cromosómica o un defecto estructural varía entre 3 por ciento y 5 por ciento. Si bien los avances en el tratamiento del feto presentan limitaciones, la evaluación antenatal fetal ha mejorado en forma considerable. En los últimos años, los avances en técnicas de imagen, genética y procedimientos invasivos han permitido comprender la fisiopatología de muchas enfermedades y su historia natural. En comparación con la década pasada, nuevas estrategias en técnicas de screening han permitido disminuir en forma considerable los procedimientos invasivos antenatales. Aún queda mucho por hacer en parto prematuro, pre-eclampsia y parálisis cerebral fetal. Existen muchas patologías fetales en donde es posible realizar el tratamiento, obteniendo un buen resultado postnatal. Esto es una alternativa que en años anteriores no era posible realizar. Hoy en día, la normativa, la consejería a los padres, la planificación del momento del embarazo, el lugar del nacimiento y así la forma y vía del parto son inmensamente discutidos y habitualmente con una participación multidisciplinaría. En los países donde el aborto es legal, el principal objetivo de los métodos de screening es identificar a fetos afectados y dar la opción a los padres del término del embarazo.

The risk to any pregnant couple of having a liveborn infant with a chromosomal abnormality or structural defect is between 3 percent and 5 percent. Though advances in fetal treatment are limited, progress in fetal evaluation has been considerable. The advances in the last years in imaging technics, genetic and invasive technics as well as a better understanding physiology of many fetal diseases and the natural history. New developments in screening strategies have, however, resulted in improved performance, which has decreased the use of prenatal diagnostic procedures substantially over the past decade. Still remains to a large extent the prevention of preterm labour, pre-eclampsia and cerebral palsy. Many fetal conditions exist for which treatment is possible and gives a good postnatal outcome. This is an option that years ago would have been denied them. Extensive discussion and parental counselling, often interdisciplinary, is the norm, and careful consideration is given to timing, method, and place of delivery.

Tratamiento endovascular con «stent cubierto» de fístula arteriovenosa secundaria a biopsia renal percutánea / Endovascular treatment with "covered stent" of arteriovenous fistula secondary to percutaneous renal biopsy

No disponible

Application of receiver operating characteristics curve (ROC) analysis when definitive and suspect morphologic flags appear in the new Coulter LH 750 analyzer.

Workflow efficiency is important in every laboratory. Manual assessment of white blood cell counts and differentials that have been rejected by an automated analyzer is one of the most time-consuming tasks in the routine hematology laboratory. In this study, receiver operating characteristics (ROC) curve analysis was used for the first time when anomalous distribution and suspect flag alarms appeared in hemograms carried out with the new Beckman Coulter LH 750 analyzer. This article is our second about the LH 750 analyzer published in this journal; we increased the number of cases and describe the novel application of statistical analysis of ROC curves. In processing of specimens from patients with 3% to 6% immature granulocytes (myelocytes + metamyelocytes + bands ), the suspect flag Imm Ne 1 (immature granulocytes) showed 77% diagnostic efficiency with a maximum area under curve (AUC) of 0.71 and a 95% confidence interval (CI) of 0.597 to 0.831 without significant differences between the 3 available levels of alarms in the analyzer (L1, L2, L2). In processing of specimens from patients with >6% immature granulocytes, the Imm Ne 1 flag showed superior diagnostic efficiency of 98% with a maximum AUC of 0.80 and a CI of 0.713 to 0.879. The suspect flag Imm Ne 2 in processing of specimens from patients with >6% of immature granulocytes showed diagnostic efficiency of 92% with a maximum AUC of 0.77 and a CI of 0.665 to 0.871, finding a significant positive difference in level L3 regarding sensitivity in comparison with the other 2 levels of the analyzer (L1, L2). For specimens from patients with >2% blasts, the suspect Blasts alarm showed a diagnostic efficiency of 94%, an AUC of 0.91, and a CI of 0.775 to 1.043; positive differences were observed between the levels L2/L3 and L1. In processing of specimens with variant lymphocytes (large, granular, prolymphocytes, cleaved, chronic lymphocytic leukemia type, and so forth) >10% (x = 14%), the suspect alarm Var Lym (variant lymphocytes) showed a low diagnostic sensitivity of 20% with a maximum AUC of 0.59 and a CI of 0.300 to 0.870 without significant differences between the 3 available levels (L1, L2, L3). However, in processing of specimens presenting values >10% reactive or activated lymphocytes (x = 23%), typical for patients with infectious mononucleosis, the Var Lym flag showed a superior sensitivity of 75% with a diagnostic efficiency of 92% and an AUC of 0.84 with a CI of 0.587 to 1.089. Finally, the laboratory can easily program definitive abnormal morphological flags of distribution (granulocytosis, eosinophilia, monocytosis, and so forth) on the basis of its patient population. In this study we were able to carry out comparisons of AUC and to choose the values for the automated counts in percentage, absolute value, or both. Therefore we were able to define the reliability and impact on the alarm routine to optimize the performance of the user-adjustable definitive alarms for anomalous distribution.

Validation of the Coulter LH 750 in a hospital reference laboratory.

Validation of the Coulter LH 750 was carried out in our central hospital laboratory, which processes 1500 hemograms per day for patients admitted into the 4 hospitals of our hospital complex and their corresponding outpatient departments. It is the reference laboratory for the provincial health care area. The analytical quality and the practical use of the instrument were studied, and we obtained within- and between-run imprecision estimates with reference controls of between 0.24% and 2.56% and inaccuracies of between -1.32% and 3.07% for basic hemogram parameters. Similar results were obtained with specimens from patients, with imprecision estimates between 0.56% and 2.56%. Linearity estimates were between 0.3 x 10(9)/L and 380 x 10(9)/L for leukocytes and between 3 x 10(9)/L and 1900 x 10(9)/L for platelets. The instrument evaluation was completed with a study of interference by bilirubin, lipemia, hemolysis, platelet clumps, and heparin and an examination of other variables, including carryover, detection limits, and the correlation of results with those of the Coulter Gen-S. A special evaluation was made of the new erythroblast count feature; with reference controls, imprecision estimates for this count were 10% to 12%, and with patient specimens imprecision averaged 10.39% up to 4 erythroblasts per 100 leukocytes. We also studied the correlation of LH 750 results and interferences with those of the manual reference method. Finally, National Committee for Clinical Laboratory Standards protocols were used to test for suspect and confirmation flags in leukocyte differential counts for 258 specimens representative of our routine. The practicability of the analyzer was studied in terms of technical difficulty, speed, and cost; also evaluated were new software elements for validation by source clinic and pathology and for reference values based on age. In conclusion, we analyzed the impact and improvements that may be expected in our laboratory (a user of Technicon and Coulter instruments) from introducing the new LH 750 analyzer into our routine.

A marine snail neurotoxin shares with scorpion toxins a convergent mechanism of blockade on the pore of voltage-gated K channels.

kappa-Conotoxin-PVIIA (kappa-PVIIA) belongs to a family of peptides derived from a hunting marine snail that targets to a wide variety of ion channels and receptors. kappa-PVIIA is a small, structurally constrained, 27-residue peptide that inhibits voltage-gated K channels. Three disulfide bonds shape a characteristic four-loop folding. The spatial localization of positively charged residues in kappa-PVIIA exhibits strong structural mimicry to that of charybdotoxin, a scorpion toxin that occludes the pore of K channels. We studied the mechanism by which this peptide inhibits Shaker K channels expressed in Xenopus oocytes with the N-type inactivation removed. Chronically applied to whole oocytes or outside-out patches, kappa-PVIIA inhibition appears as a voltage-dependent relaxation in response to the depolarizing pulse used to activate the channels. At any applied voltage, the relaxation rate depended linearly on the toxin concentration, indicating a bimolecular stoichiometry. Time constants and voltage dependence of the current relaxation produced by chronic applications agreed with that of rapid applications to open channels. Effective valence of the voltage dependence, zdelta, is approximately 0.55 and resides primarily in the rate of dissociation from the channel, while the association rate is voltage independent with a magnitude of 10(7)-10(8) M-1 s-1, consistent with diffusion-limited binding. Compatible with a purely competitive interaction for a site in the external vestibule, tetraethylammonium, a well-known K-pore blocker, reduced kappa-PVIIA's association rate only. Removal of internal K+ reduced, but did not eliminate, the effective valence of the toxin dissociation rate to a value <0.3. This trans-pore effect suggests that: (a) as in the alpha-KTx, a positively charged side chain, possibly a Lys, interacts electrostatically with ions residing inside the Shaker pore, and (b) a part of the toxin occupies an externally accessible K+ binding site, decreasing the degree of pore occupancy by permeant ions. We conclude that, although evolutionarily distant to scorpion toxins, kappa-PVIIA shares with them a remarkably similar mechanism of inhibition of K channels.

Solution structure and proposed binding mechanism of a novel potassium channel toxin kappa-conotoxin PVIIA.

BACKGROUND: kappa-PVIIA is a 27-residue polypeptide isolated from the venom of Conus purpurascens and is the first member of a new class of conotoxins that block potassium channels. By comparison to other ion channels of eukaryotic cell membranes, voltage-sensitive potassium channels are relatively simple and methodology has been developed for mapping their interactions with small-peptide toxins. PVIIA, therefore, is a valuable new probe of potassium channel structure. This study of the solution structure and mode of channel binding of PVIIA forms the basis for mapping the interacting residues at the conotoxin-ion channel interface. RESULTS: The three-dimensional structure of PVIIA resembles the triple-stranded beta sheet/cystine-knot motif formed by a number of toxic and inhibitory peptides. Subtle structural differences, predominantly in loops 2 and 4, are observed between PVIIA and other conotoxins with similar structural frameworks, however. Electrophysiological binding data suggest that PVIIA blocks channel currents by binding in a voltage-sensitive manner to the external vestibule and occluding the pore. Comparison of the electrostatic surface of PVIIA with that of the well-characterised potassium channel blocker charybdotoxin suggests a likely binding orientation for PVIIA. CONCLUSIONS: Although the structure of PVIIA is considerably different to that of the alphaK scorpion toxins, it has a similar mechanism of channel blockade. On the basis of a comparison of the structures of PVIIA and charybdotoxin, we suggest that Lys19 of PVIIA is the residue which is responsible for physically occluding the pore of the potassium channel.

Modal gating in neuronal and skeletal muscle ryanodine-sensitive Ca2+ release channels.

The bursting behavior of ryanodine-sensitive single Ca2+ release channels present in chicken cerebellum endoplasmic reticulum (ER), rat hippocampus ER, and frog and rabbit skeletal muscle sarcoplasmic reticulum was established. Unconditional dwell time distributions fitted by the maximum likelihood method reveal at least three open and closed exponential components. Trains of low open probability (P(o)) bursts were interspersed with trains of high P(o) bursts (> or = 0.8) in all the ryanodine receptor isotypes tested. The gating kinetics of the Ca2+ release channels were defined in long recordings by analyzing burst sequences and gamma distributions of average intraburst open (T(o)) and closed times (Tc). The gamma distributions of T(o) had two gamma components, suggesting the existence of two distinct burst types. In contrast, the gamma distributions of Tc had only one component. The correlation between consecutive burst pairs was defined in terms of T(o) and then statistically tested by 2 x 2 matrix contingency analysis. The probability that the ubiquitous sequential burst pattern was generated by random occurrence was < 0.01 (two-tailed Fisher's exact test). Temporal correlations were observed in all ryanodine receptor isotypes under a variety of experimental conditions. These data strongly suggest that single Ca2+ release channels switch slowly between modes of gating. We propose that the effects of agonists of Ca2+ release channels such as Ca2+ itself can be explained as concentration-dependent changes in the availability of each mode.