Activation of ATP-Sensitive Potassium Channels Underlies Contractile Failure in Single Human Cardiac Myocytes During Complete Metabolic Inhibition

ATP-Sensitive Potassium Channels in Human Heart. Introduction: The purpose of this study was to examine the electrophysiologic derangements that underlie contractile failure in single human heart muscle cells exposed to metabolic inhibition. Methods and Results: Single myocytes were isolated from right atrial appendage specimens obtained intraoperatively from patients undergoing routine cardiac surgery. On exposure to lO-mM 2-deoxyglucose (to inhibit glycolysis) and 2-mM cyanide (to inhibit oxidative phosphorylation), twitch shortening decreased to undetectable levels over 5–6 minutes. The action potential duration declined in parallel with the contractile failure. Using voltage clamp depolarizations of a fixed duration the twitch was maintained in metabolic blockade until the development of maintained (rigor) contracture. At this time a large increase in K⁺ conductance, which can be attributed to the activation of ATP-sensitive K ⁺ channels (K _ATP channels), was measured. In isolated inside-out membrane patches, the ATP dependence of K_aTP channel activity was described by a sigmoid curve with K_i,_ATP (ATP concentration required for half-maximal inhibition of K _ATPchannel activity) = 8 μM and Hill coefficient (n_H) = 1.2. The single channel current-voltage relationship reversed close to the K ⁺ equilibrium potential and the conductance was approximately linear (g = 29 pS) over the voltage range included in the action potential (-60 m V to +20 mV). Conclusion: In human atrial cardiac myocytes subjected to complete metabolic inhibition, contractile failure is caused by action potential shortening resulting from an increase in K + conductance presumably through the activation of K_ATP channels. (J Cardiovasc Electrophysiol, Vol. 3, pp. 56–63, February 1992)     

The clinical and financial impact of non-invasive vascular testing in the USA

Health care costs in the USA have increased dramatically during the past 10 years, and it is widely believed that they have reached crisis dimensions. Vascular laboratories are a segment of the USA health care industry that has experienced particularly rapid growth in the last decade. In 1992, USA Medicare payments (for patients ≥ 65 years) totalled US$304 492 588 for 3 673 695 non-invasive vascular studies. This figure represents only one segment of USA health care costs and, if all segments were considered, the 1992 total for vascular laboratory services would probably approach one billion USA dollars. The expansion of vascular laboratory utilization is attributed to a number of factors: (i) increased recognition of the clinical value of non-invasive vascular studies; (ii) replacement of invasive (angiographic) procedures; (iii) expanded surveillance application; (iv) the verification of carotid endarterectomy for treatment of carotid stenosis; (v) widespread, unlimited access; (vi) over-utilization; (vii) greed. Widespread awareness of the crisis in USA health care funding has imposed cost-containment pressure where virtually none existed previously. The vascular laboratory is no exception to this trend, and the following measures have been suggested for controlling vascular laboratory costs: (i) demonstration of the clinical and cost effectiveness of non-invasive vascular studies; (ii) utilization review; (iii) pre-approval of requests for vascular studies; (iv) linkage of vascular study reimbursement with clinical diagnosis; (v) limitations on self-referral; (vi) reduced reimbursement; (vii) capitation; (viii) diagnosis-related reimbursement; (ix) accreditation. This article summarizes the factors that have led to increased utilization of vascular laboratory services, and discusses methods proposed for containing vascular laboratory expenditure.     

Improved prediction of bone mineral content and density

To establish improved predictive values for normal bone mineral content (BMC) and density (BMD) in adolescent girls a community based study of schoolgirl volunteers was carried out by dual energy x ray absorptimetry. Measurements were performed on 216 subjects aged 11.0 to 17.9 years; measurements were repeated one year later on 84 of the girls, providing a total of 300 studies. For total body BMC the standard error of the prediction was improved from 290.9 g to 134.1 g when weight, height, and shoulder width were added to the normal variable of age. For spine BMD the standard error of the prediction was improved from 0.105 g/cm2 to 0.066 g/cm2 when height, weight, and shoulder width were added to the normal variable of age. Significant improvements were also obtained for total BMD and spine BMC. Despite the normal practice of predicting bone density from age alone this was not selected as the first variable in a multiple stepwise regression for either total body or spine. The prediction of BMC and BMD can be significantly improved by the inclusion of simple body habitus parameters in the prediction equations. As the mean (SE) z score derived from the manufacturer's normal data was - 0.36 (0.02) these American data are probably not appropriate for use in adolescents in the UK.     

Staghorn calculi: endourologic management in 120 patients

Symptomatic staghorn renal calculi were removed from 106 of 124 kidneys (85%) with percutaneous ultrasonic lithotripsy. All remaining fragments were less than 5 mm in greatest diameter, small enough to pass spontaneously. Use of two or more access routes was necessary in 91 kidneys (73%), and 29 patients (24%) required multistage nephrolithotripsy for complete stone removal. The total operative time averaged 162 minutes per patient. The average hospitalization period was 12.5 days, and the average convalescence time after discharge was 15 days. The most common adverse effect was bleeding necessitating transfusion (57%). Infection occurred in 27% of patients and may be intrinsic to removal of these infected stones. There was one death in the study group: a patient with multiple medical problems died of myocardial infarction. Successful stone extraction requires a clear understanding of renal anatomic features, properly placed access routes, and radiologic-urologic expertise. It is concluded that staghorn calculi can be safely and effectively treated with the use of percutaneous techniques.     

胆红素IXα在碱溶液中的荧光性质和异构化作用

研究了朋红素IX_α的荧光性质,发现胆红素IX_α在碱溶液中有较强的特征荧光,考察了影响胆红素碱溶液荧光性质及其稳定性的因素,时间扫描的荧光动力学研究表明胆红素IX_α碱溶液在30min内有足够稳定的强荧光信号,这对建立胆红素的荧光分析方法有重要意义。从胆红素IX_α的碱溶液中分离出荧光活性物,结构分析认为是胆红素IX_α的某一异构体。讨论了胆红素IX_α的异构化作用与胆红素IX_α碱溶液荧光性质的变化规律。