The voltage-dependent potassium channel subunit Kv2.1 regulates insulin secretion from rodent and human islets independently of its electrical function.

AIMS/HYPOTHESIS: It is thought that the voltage-dependent potassium channel subunit Kv2.1 (Kv2.1) regulates insulin secretion by controlling beta cell electrical excitability. However, this role of Kv2.1 in human insulin secretion has been questioned. Interestingly, Kv2.1 can also regulate exocytosis through direct interaction of its C-terminus with the soluble NSF attachment receptor (SNARE) protein, syntaxin 1A. We hypothesised that this interaction mediates insulin secretion independently of Kv2.1 electrical function. METHODS: Wild-type Kv2.1 or mutants lacking electrical function and syntaxin 1A binding were studied in rodent and human beta cells, and in INS-1 cells. Small intracellular fragments of the channel were used to disrupt native Kv2.1-syntaxin 1A complexes. Single-cell exocytosis and ion channel currents were monitored by patch-clamp electrophysiology. Interaction between Kv2.1, syntaxin 1A and other SNARE proteins was probed by immunoprecipitation. Whole-islet Ca(2+)-responses were monitored by ratiometric Fura red fluorescence and insulin secretion was measured. RESULTS: Upregulation of Kv2.1 directly augmented beta cell exocytosis. This happened independently of channel electrical function, but was dependent on the Kv2.1 C-terminal syntaxin 1A-binding domain. Intracellular fragments of the Kv2.1 C-terminus disrupted native Kv2.1-syntaxin 1A interaction and impaired glucose-stimulated insulin secretion. This was not due to altered ion channel activity or impaired Ca(2+)-responses to glucose, but to reduced SNARE complex formation and Ca(2+)-dependent exocytosis. CONCLUSIONS/INTERPRETATION: Direct interaction between syntaxin 1A and the Kv2.1 C-terminus is required for efficient insulin exocytosis and glucose-stimulated insulin secretion. This demonstrates that native Kv2.1-syntaxin 1A interaction plays a key role in human insulin secretion, which is separate from the channel's electrical function.

Direct interaction of a brain voltage-gated K+ channel with syntaxin 1A: functional impact on channel gating.

Presynaptic voltage-gated K(+) (Kv) channels play a physiological role in the regulation of transmitter release by virtue of their ability to shape presynaptic action potentials. However, the possibility of a direct interaction of these channels with the exocytotic apparatus has never been examined. We report the existence of a physical interaction in brain synaptosomes between Kvalpha1.1 and Kvbeta subunits with syntaxin 1A, occurring, at least partially, within the context of a macromolecular complex containing syntaxin, synaptotagmin, and SNAP-25. The interaction was altered after stimulation of neurotransmitter release. The interaction with syntaxin was further characterized in Xenopus oocytes by both overexpression and antisense knock-down of syntaxin. Direct physical interaction of syntaxin with the channel protein resulted in an increase in the extent of fast inactivation of the Kv1.1/Kvbeta1.1 channel. Syntaxin also affected the channel amplitude in a biphasic manner, depending on its concentration. At low syntaxin concentrations there was a significant increase in amplitudes, with no detectable change in cell-surface channel expression. At higher concentrations, however, the amplitudes decreased, probably because of a concomitant decrease in cell-surface channel expression, consistent with the role of syntaxin in regulation of vesicle trafficking. The observed physical and functional interactions between syntaxin 1A and a Kv channel may play a role in synaptic efficacy and neuronal excitability.

Modulation by protein kinase C activation of rat brain delayed-rectifier K+ channel expressed in Xenopus oocytes.

The modulation by protein kinase C (PKC) of the RCK1 K+ channel was investigated in Xenopus oocytes by integration of two-electrode voltage clamp, site-directed mutagenesis and SDS-PAGE analysis techniques. Upon application of beta-phorbol 12-myristate 13-acetate (PMA) the current was inhibited by 50-90%. No changes in the voltage sensitivity of the channel, changes in membrane surface area or selective elimination of RCK1 protein from the plasma membrane could be detected. The inhibition was mimicked by 1-oleoyl-2-acetyl-rac-glycerol (OAG) but not by alphaPMA, and was blocked by staurosporine and calphostin C. Upon deletion of most of the N-terminus a preceding enhancement of about 40% of the current was prominent in response to PKC activation. Its physiological significance is discussed. The N-terminus deletion eliminated 50% of the inhibition. However, phosphorylation of none of the ten classical PKC phosphorylation sites on the channel molecule could account, by itself or in combination with others, for the inhibition. Thus, our results show that PKC activation can modulate the channel conductance in a bimodal fashion. The N-terminus is involved in the inhibition, however, not via its direct phosphorylation.

[Effect of thrombolytic, anticoagulant and anti-thrombocytic therapy on the development of left-ventricular thrombosis and the incidence of thromboembolic complications in patients with myocardial infarction]. / Vliianie tromboliticheskoi iantitrombotsitarnoi terapii na razvitie tromboza levogo zheludochka i chastoty tromboémbolicheskikh oslozh- nenii u bol'nykh infarktom miokarda.

To reveal the effects produced by thrombolytic and anticoagulative therapies on the formation of left ventricular mural thrombosis (LVT) and the frequency of thromboembolic events, a prospective randomized study was performed in 285 patients with primary transmural myocardial infarction. LVT was diagnosed from the serial two-dimensional echocardiographic findings. No significant effect of the therapy with thrombolytic and anticoagulative agents was found on the incidence and periods of intracavitary LVT development. There was a significant reduction in the incidence of LVT during early (less than 3 hours) reperfusion of the occluded coronary artery. Anticoagulative and antiplatelet therapies performed within the first month of myocardial infarction decrease the risk for systemic thromboembolism in patients with diagnosed LVT.

[Evaluation of the overall contractile function of the right ventricle using two-dimensional echocardiography in patients with myocardial infarction]. / Otsenka obshchei sokratitel'noi funktsii pravogo zheludochka s pomoshch'iu dvukhmernoi ékhokardiografii u bol'nykh infarktom miokarda.

The paper presents two methods for calculating the contractile function of the right ventricle (RV): (1) three-plane one with the use of short- and long-axis-cut RV; (2) single-plane one which was modified to the use of long-axis RV images in the projection of 4 chambers. A total of 56 patients with first acute gross myocardial infarction were studied. A control group included 14 healthy subjects aged 25-60 years. The proposed three-plane method for estimating the volume parameters and ejection fraction of the right ventricle was shown to correlate with contrast ventriculography significantly. A high correlation was found between the stroke output of RV (as calculated for the left ventricle by the Chapman method) and that (by the three-plane method). The RV volume values in patients with anterior or inferior myocardial infarction suggest that there is a trend to suppress RV function in the patients, but it is more specific for those with inferior myocardial infarction.

[Evaluation of the informative value and safety of the transesophageal atrial electric stimulation test in patients with unstable stenocardia and myocardial infarction (data of 24-hour ECG monitoring)]. / Otsenka informativnosti i bezopasnosti proby s chrespishchevodnoi élektricheskoi stimuliatsiei predserdii u bol'nykh s nestabil'noi stenokardiei i infarktom miokarda po dannym sutochnogo monitorirovaniia EKG.

The effect of the transesophageal pacing test (TEPT) on the occurrence of ventricular arrhythmias and ischemic episodes was examined on the basis of 24-hour ECG monitoring in patients with unstable angina (UA) and myocardial infarction (MI). It is demonstrated that TEPT is a relatively safe test for UA and MI patients (to be performed on day 10-14), which does not provoke severe arrhythmias during and after the testing, but for short paroxysms of ventricular tachycardia seen in 2-4% of the cases. Both painful and painless ST displacements were recorded during the test; ST elevation was only noted in MI patients. The time of ECG baseline recovery was longer in painful ischemic episodes, as compared to painless ones. The TEPT test is a valuable instrument for detecting latent atrioventricular conductivity disorders in UA and MI patients.

[Hemodynamic effects of intravenous allapinine in patients with myocardial infarction]. / Vliianie vnutrivennogo vvedeniia allapinina na gemodinamiku u bol'nykh infarktom miokarda.

Single intravenous allapinine, 30 mg, given to patients with acute myocardial infarction, including those with moderate circulatory insufficiency, fails to affect central hemodynamic parameters or has a favourable action: normalizes pulmonary diastolic pressure, cardiac index, diminishes total peripheral vascular resistance. The agent also produces a weak antihypertensive effect and increases heart rate.

[Effects of restored blood flow on the contractile function of the right ventricle in patients with acute myocardial infarct: data of two-dimensional computerized echocardiography]. / Vliianie vosstanovleniia krovotoka na sokratitel'nuiu funktsiiu pravogo zheludochka u bol'nykh ostrym infarktom miokarda po dannym dvukhmernoi kompiuternoi ékhokardiografii.

The volumes of the right and left ventricles were measured in 78 patients with first acute transmural myocardial infarction at days 1, 3, 7, 14, and 28 of the disease. Thirty four patients were diagnosed as having anterior myocardial infarction, 35 presented with inferior myocardial infarction, and 9 had a concurrent right and left ventricular inferior wall myocardial infarction. A high incidence of right ventricular dysfunction was confirmed both in anterior and inferior myocardial infarction. The most profound right ventricular contractile dysfunctions were detected in patients with proximal right coronary occlusion in the absence of reperfusion. Successful thrombolytic therapy for myocardial infarction was found to affect right ventricular function to a lesser extent than left function.

[Study of the effect of the restoration of coronary blood flow on left-ventricular contractility in patients with acute myocardial infarction based on the data of computerized two-dimensional echocardiography]. / Vliianie vosstanovleniia koronarnogo krovotoka na sokratitel'nuiu funktsiiu levogo zheludochka u bol'nykh ostrym infarktom miokarda po dannym komp'iuternoi dvukhmernoi ékhokardiografii.

Total and local left-ventricular contractility was assessed by computerized two-dimensional echocardiography in 52 patients with acute myocardial infarction. Three groups of patients were identified: those with recovered coronary flow (group 1), reperfusion failure (group 2) and the lack of occlusion at first coronarography (group 3). Patients from group 3 showed the most intact left-ventricular myocardial contractility and the most favorable clinical course of the disease, while second-group patients had particularly impaired left-ventricular contractility. In the first group, the size of the asynergic area diminished by day 28 of the disease to a greater extent, as compared to the second group. Therefore, coronary reperfusion within the first 6 hours after the attack shows correlation to a smaller asynergic zone and a more favorable clinical course of the disease.

[Computerized two-dimensional echocardiography in acute myocardial infarction. Possibility of determining the size of necrotic focus]. / Komp'iuternaia dvukhmernaia eknokardiografiia pri ostrom infarkte miokarda. Vozmozhnosti opredeleniia razmerov ochaga porazheniia.

Myocardial asynergic area was estimated, using a new special mathematical model based on computerized assessment of echocardiographic images, in 42 patients with first acute transmural myocardial infarction. The results were compared with those of other standard methods used for the estimation of the size of damage, and with morphologic findings in 7 fatal cases. The latter comparison demonstrated that the special estimate of asynergic area, unlike the planimetric method, used earlier, showed a high correspondence to the actual size of damage. The comparison of echocardiographic data to those obtained by other techniques showed a significant correlation with the results of serial MB CFK assays and myocardial 201Tl scintigraphy.

[Determination of the right ventricular volume and ejection fraction by echocardiography (a comparison with angiographic data)]. / Opredelenie ob''ema i fraktsii vybrosa pravogo zheludochka pri pomoshchi ékhokardiografii (sopostavlenie s angiograficheskimi dannymi).

The determination of function of all cardiac chambers is important in clinical practice. The improvement of the method of two-dimensional echocardiography permitting visualization of the right ventricle (RV) in different topographic projections made possible ultrasonic assessment of RV function. The RV volume and ejection fraction were determined by two-dimensional echocardiography in 25 patients and the results obtained were compared with contrast ventriculography findings. Taking into account the complexity of geometrical shape of the right ventricle its volume based on the results of echocardiography, equaled the sum of the volumes of 3 figures: 2 frusta and one cone. Comparing the results obtained by two methods, significant correlation of all indices characterizing RV function (r-0.85-0.89) was revealed. The prospects of future development of the calculation of RV volumetric indices by the results of two-dimensional echocardiography were discussed. Limitations of the use of this method were described.

[Diagnosis of thrombosis of the left ventricle in patients with acute myocardial infarction using 2-dimensional echocardiography]. / Diagnostika tromboza levogo zheludochka u bol'nykh ostrym infarktom miokarda metodom dvukhmernoi ékhokardiografii.

The authors demonstrate the possibilities of two-dimensional echocardiography in the diagnosis of left ventricular thrombosis (LVT) with special reference to patients with acute myocardial infarction (AMI). Provide the data of echocardiographic examination of 34 patients with transmural AMI. LVT was identified in 8 patients with anterior AMI. The authors show the relationship between the development of LVT and the site and extent of lesion, and the degree of left ventricular contractility disorders. Outline the prospects of further studies into LVT in patients with AMI.

[Normal indices of left ventricular function assessed by using computer technology]. / Normal'nye pokazateli funktsional'nogo sostoianiia levogo zheludochka, otsenennye s primeneniem komp'iuternoi tekhniki.

While analysing ventriculograms of 18 persons without any cardiovascular pathology 3 "independent" research workers (to exclude a subjective factor in the appraisal of the left ventricle contours) have developed normal indicators of the total and regional contractility of the left ventricle. The data obtained with the use of angiographic and computer-aided techniques of the recent generation and machine analysis employing unpaired statistics can be recommended for application as normal indicators during the performance of different hemodynamic studies.

[Embolism of the anterior descending artery as a cause of myocardial infarct in a patient with a prosthetic aortic valve]. / Emboliia peredenei niskhodiashchei arterii kak prichina infarkta miokarda u bol'nogo s protezom aortal'nogo klapana.

A patient aged 42 with the aortic valve prosthesis was examined with the help of coronography and ultrasonic scanning of the heart in the period of ischemic injury of the anterior myocardium: occlusion of the unchanged anterior descending artery by an embolus formed on the artificial cardiac valve was revealed. Despite rapid recovery of arterial permeability (3 h 47 min, after the onset of disease) by intracoronary administration of streptase with subsequent anticoagulant and antiplatelet drug therapy the patient developed anterior myocardial infarction with left ventricular aneurysm and intracardiac thrombosis.

[Modern methods for the instrumental diagnosis of intracavitary thrombosis of the left ventricle in myocardial infarct]. / Sovremennye metody instrumental'noi diagnostiki vnutripolostnogo tromboza levogo zheludochka pri infarkte miokarda.

To study the sensitivity and specificity of two-dimensional echocardiography in the diagnosis of left ventricle thrombosis which often attends myocardial infarction and to define diagnostic potentialities of the new research methods (digital subtraction ventriculography and MR tomography), 449 patients with acute transmural myocardial infarction were examined. Based on the comparison of the echocardiographic readings and morbid anatomy data it has been shown that the sensitivity of two-dimensional echocardiography in revealing left ventricle thrombosis amounts to 89%, specificity to 88%. Digital subtraction ventriculography has a lower (77%) sensitivity, with the specificity being satisfactory enough (88%). Meanwhile MR tomography enables a highly precise diagnosis of left ventricle thrombosis and can be used as a supplementary diagnostic method in questionable cases and in thrombi small in size or in unsatisfactory ultrasonic visualization of the heart structures.

[The action of triftorfenazin on the Ca-ATPase activity of fibroblasts and Ehrlich ascites cells]. / Deistvie triftorfenazina na aktivnost' Ca-ATFazy fibroblastov i astsitnykh kletok Erlikha.

The authors studied the mechanisms underlying the increase of the Ca-ATPase activity in tumoral cells. The kinetic analysis showed that Michaelis constant for ATP was higher in comparison with proliferating cells.

[Postradiation changes in the activity of membrane-bound nerve tissue enzymes]. / Postradiatsionnye izmeneniia aktivnosti membranosviazannykh fermentov nervnoi tkani.

A study was made of the effect of various radiation doses (1.75 to 12.25 Gy) on the enzyme activity of Na,K-ATPase system of the microsomal brain fraction of mongrel and Wistar rats. With a similar method of the fraction isolation different response of the activity of this enzyme was registered. Different radiosensitivity of M9-ATPase is responsible for the direction of changes in the Na,K-ATPase activity of the preparations.

[The radiomodifying action of ATP and ADP on membrane-bound enzymes]. / Radiomodifitsiruiushchee deistvie ATF i ADF na membranosviazannye fermenty.

A modifying action of ATP and ADP on the activity of some key membrane-bound enzymes of the brain and heart microsomes of rats exposed to 7 Gy radiation has been investigated. The difference in the reactions of energy-dependent enzymes is attributed to the compensatory systems involved at the molecular level.