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At least 649 records · Page 36Linked to original sources
PubMed1994

[Effects on hemodynamics and myocardial metabolism of nicardipine and nitroglycerin during aortic cross clamp in dogs with experimentally produced coronary stenosis].

We investigated the effects of hemodynamics and myocardial metabolism of nicardipine (NIC) and nitroglycerin (NTG) in experimentally coronary constricted dogs. Coronary constriction was produced by reducing 50% of the left anterior descending coronary blood flow. After stabilization of hemodynamics, we cross-clamped the descending aorta and administered nicardipine (10 micrograms.kg-1.min-1) or nitroglycerin (10 micrograms.kg-1.min-1). The drugs were infused for 15 minutes and were discontinued just before the clamp on the aorta was released. In NIC group, the cardiac output (CO) increased 32% and the heart rate (HR) decreased 17% significantly, compared with pre-clamping values. The myocardial blood flow (MBF) in ischemic area measured by hydrogen clearance method was maintained. The value of the myocardial oxygen extraction ratio (MO2EX) decreased significantly for 24.3% compared with the pre-clamping value of 41.4%. On the other hand, in NTG group, CO, HR, and MO2EX were unchanged, but MBF in ischemic area was well maintained. The results of these experimentally coronary constricted dogs suggest that both NIC and NTG maintain the cardiac function during the aortic cross-clamping, but regarding the improvement of the myocardial metabolism, NIC appears to be the better choice for blood pressure control.

Animals↗
PubMed1993

[Safe and accurate coronary artery bypass grafting: combined use with single aortic clamp and retrograde coronary perfusion].

Neurological injury following myocardial revascularization may result from embolization of atheromatous debris from clamping the diseased aorta. The hazards of manipulating and clamping the aorta has been reported in some literatures. The proximal anastomoses with partial occluding clamp is conventional technique, but it may cause neurological injury, aortic tear or traumatic laceration. We developed a technique for coronary bypass grafting with single aortic cross clamp and combined antegrade/retrograde infusion of cardioplegia. Our method allows accurate performance of the proximal anastomosis without partial clamping and adequate protection of myocardium.

Aorta↗
PubMed1996

Comparison of herniorrhaphy versus clamping of umbilical hernias in horses: a retrospective study of 93 cases (1982-1994).

Many uncomplicated umbilical hernias have been managed successfully in foals by the application of a hernia clamp. Isolated reports of complications following clamp application have led some authors to suggest that it is an unsuitable method of treatment. Little information has been published comparing the complication rates associated with the use of hernia clamps and herniorrhaphy in the treatment of umbilical hernias. The purpose of this retrospective study was to report the characteristics of clinical cases of umbilical hernia and to compare the complication rates following these 2 treatment approaches. Information was collected from records or from owners to identify the occurrence of complications and owner satisfaction following treatment. Of 93 cases, 10 complicated and 18 uncomplicated hernias were treated by herniorrhaphy, 40 uncomplicated hernias were treated by clamping, 1 originally uncomplicated hernia was treated by both techniques, and 24 cases were untreated. Nineteen percent of uncomplicated hernias treated by herniorrhaphy, and 19% of those clamped developed minor complications. This study demonstrates that although minor complications may be associated with either technique, they generally do not result in significant morbidity.

Animals↗
PubMed1996

Effect of sodium nitroprusside on cerebral haemodynamics during cross-clamping of the descending thoracic aorta in pigs.

OBJECTIVE: To assess the effect of sodium nitroprusside on cerebral haemodynamics during cross-clamping of the descending thoracic aorta in pigs. DESIGN: Non-randomised controlled animal study. SETTING: University hospital, Norway. MATERIAL: 17 Pigs. INTERVENTIONS: Cross-clamping of the descending thoracic aorta for 30 minutes. In 8 pigs sodium nitroprusside was given to prevent proximal hypertension (sodium nitroprusside group); 9 pigs were given no sodium nitroprusside (control group). MAIN OUTCOME MEASURES: Intracerebral pressure, sagittal sinus pressure, cerebral flux, and internal carotid artery blood flow. RESULTS: Intracerebral pressure, sagittal sinus pressure, and cerebral flux increased in both groups during cross-clamping of the descending thoracic aorta. There were no differences between the groups in these variables despite significantly lower mean proximal aortic pressure in the sodium nitroprusside group. CONCLUSIONS: Sodium nitroprusside did not affect intracerebral pressure, sagittal sinus pressure, or cerebral flux during cross-clamping of the descending thoracic aorta. Increased cerebral blood flow rather than venous congestion is the most likely cause of increased intracranial pressure during cross-clamping of the descending thoracic aorta.

Animals↗
PubMed1976

Unimpaired renal, myocardial and neurologic function after cross clamping of the thoracic aorta.

Twelve patients who had sustained trauma presented at the emergency department with either asystole or profound hypotension. All underwent thoracotomy and temporary cross clamping of the descending thoracic aorta as part of the resuscitative measures; all received massive amounts of fluids and cold blood and underwent prompt surgical intervention. In none of these patients was there evidence of myocardial, peripheral nerve, neurologic or renal damage. One patient had residual cortical blindness. Measures were taken to preserve renal function before, during and after aortic cross clamping. These included the avoidance of nephrotoxic antibiotics, limit of clamping time to the minimum effective period, intermittent release of the aortic clamp, and intraoperative administration of osmotic diuretics or furosemide, or both. Other factors which may have contributed to these results were the youth of these patients, the absence of cardiac, renal or metabolic diseases and the hypothermia resulting from the administration of large amounts of cold blood. We concluded that temporary cross clamping of the descending thoracic aorta should be performed only for patients with massive exsanguine trauma who have cardiac arrest or who do not respond to other intensive resuscitative measures.

Adolescent↗
PubMed1997

The postoperative drain-clamping method for hemostasis in total knee arthroplasty. Reducing postoperative bleeding in total knee arthroplasty.

We attempted to decrease the amount of postoperative bleeding after total knee arthroplasty (TKA) by clamping the suction drain and through retrograde infusion of saline containing a low concentration of epinephrine. When TKA was completed and the sutured wound was bandaged, 50 ml of saline containing epinephrine diluted to 1:200,000 and 0.5 g of antibiotic was injected into the knee joint via the inserted suction drain. The drain was clamped for 20 hours and then unclamped to begin aspiration until 48 hours after surgery. To clarify the effectiveness of this method, patients were divided into three groups. Group I consisted of 116 knees (in 95 patients) infused with 50 ml saline containing a low dose of epinephrine: Group II was composed of 70 knees (42 patients) infused with 50 ml saline only; and Group III included 97 knees (78 patients) who did not undergo this drain-clamp method. The average amount of postoperative bleeding was 207 ml in Group I, 255 ml in Group II (p < 0.01), and 501 ml in Group III (p < 0.001). With this method of using saline with a low dose of epinephrine and sustained clamping of up to 20 hours, we have been able to operate on elderly patients with rheumatoid arthritis without blood transfusion, even in cases of simultaneous bilateral TKA. Drain-clamping with saline infusion effectively controlled postoperative bleeding after TKA, and when epinephrine was added to the saline, the hemostatic effect was even greater than that of saline alone.

Adult↗
PubMed1978

Nitroglycerin infusion during infrarenal aortic cross-clamping in dogs: an experimental study.

The effects of an intravenous infusion of nitroglycerin on cardiac index and peripheral vascular resistance during infrarenal aortic cross-clamping were determined in normal animals and in animals subjected to low cardiac output state. Both groups of untreated animals demonstrated progressive fall in cardiac index with a rise in total peripheral resistance during infrarenal aortic cross-clamping. The infusion of nitroglycerin during the period of aortic cross-clamping prevented the increase in total peripheral resistance and therefore prevented the progressive fall in cardiac index that occurred in untreated animals. In the animals with depressed myocardial function, the infusion of nitroglycerin produced a 44% increase in cardiac index during aortic cross-clamping. The results of this study showed that the infusion of nitroglycerin during abdominal aortic cross-clamping can prevent adverse cardiovascular sequelae from occurring and should be used in patients undergoing abdominal aortic resection, especially those with impairment of left ventricular function.

Animals↗
PubMed2002

Feasibility, safety and image quality of cardiac FDG studies during hyperinsulinaemic-euglycaemic clamping.

Fluorine-18 fluorodeoxyglucose (FDG) imaging for the assessment of myocardial viability has become an integral part of the diagnostic and prognostic work-up of patients with ischaemic cardiomyopathy. To ensure good image quality, in particular in patients with diabetes mellitus, hyperinsulinaemic-euglycaemic clamping has been proposed. In this study we evaluated the safety and the image quality of cardiac FDG imaging during clamping in a large group of patients, including a subgroup with diabetes mellitus. The incidence of viability (on both a segment and a patient basis) was also determined for patients with and without diabetes mellitus. The safety and image quality of cardiac FDG studies during clamping were evaluated in 131 patients, including 19 with diabetes mellitus. Image quality was assessed visually and quantitatively using heart-to-lung (H/L), heart-to-liver (H/Li) and myocardium-to-background (M/B) ratios. Blood samples were drawn at baseline and at the time of FDG injection to determine levels of glucose, free fatty acids and insulin. The metabolic circumstances were optimal for FDG imaging: high insulin levels, low free fatty acid levels and glucose levels in the normal range (levels of substrates were comparable between patients with and patients without diabetes mellitus). No serious side-effects occurred in any patient. Image quality (assessed visually) was good in all patients. The quantitative parameters of image quality (H/L, H/Li and M/B) were comparable between patients with and patients without diabetes mellitus. The incidence of viability was high: 38% of patients without and 58% of patients with diabetes mellitus had substantial viability despite contractile dysfunction. It is concluded that cardiac FDG imaging during clamping is safe and provides excellent image quality, including in patients with diabetes mellitus. The incidence of viability is high, in particular in patients with diabetes mellitus.

Aged↗
PubMed2000

Dendrimer-assisted patch-clamp sizing of nuclear pores.

Macromolecular translocation (MMT) across the nuclear envelope (NE) occurs exclusively through the nuclear pore complex (NPC). Therefore, the diameter of the NPC aqueous/electrolytic channel (NPCC) is important for cellular structure and function. The NPCC diameter was previously determined to be approximately equal to 10 nm with electron microscopy (EM) using the translocation of colloidal gold particles. Here we present patch-clamp and fluorescence microscopy data from adult cardiomyocyte nuclei that demonstrate the use of patch-clamp for assessing NPCC diameter. Fluorescence microscopy with B-phycoerythrin (BPE, 240 kDa) conjugated to a nuclear localization signal (NLS) demonstrated that these nuclei were competent for NPC-mediated MMT (NPC-MMT). Furthermore, when exposed to an appropriate cell lysate, the nuclei expressed enhanced green fluorescence protein (EGFP) after 5-10 h of incubation with the plasmid for this protein (pEGFP, 3.1 MDa). Nucleus-attached patch-clamp showed that colloidal gold particles were not useful probes; they modified NPCC gating. As a result of this finding, we searched for an inert class of particles that could be used without irreversibly affecting NPCC gating and found that fluorescently labeled Starburst dendrimers, a distinct class of polymers, were useful. Our patch-clamp and fluorescence microscopy data with calibrated dendrimers indicate that the cardiomyocyte NPCC diameter varies between 8 and 9 nm. These studies open a new direction in the investigation of live, continuous NPC dynamics under physiological conditions.

Animals↗
PubMed1988

The glucose stimulus-response curve of the beta-cell in physically trained humans, assessed by hyperglycemic clamps.

In order to examine the effect of habitual exercise on beta-cell responses over a wide range of plasma glucose levels, plasma insulin and C-peptide responses to 2 1/2-hour hyperglycemic clamps at 7.5, 10, and 15 mmol/L glucose were assessed in six trained athletes and six age- and weight-matched sedentary controls. Athletes were significantly fitter than controls (estimated maximal oxygen uptake [VO2 max] mean 44 v 30 mL.kg-1.min-1, P less than .05) and were more sensitive to insulin as assessed by dividing the mean glucose infusion rate over the last 20 minutes of the clamp by the steady-state plasma insulin (mean 0.44 v 0.19 mg.min-1.kg-1.nmol-1. L, respectively, P less than .01). Plasma C-peptide responses were lower in the athletes, both fasting (geometric mean 0.28 v 0.62 nmol/L, P less than .05), and at the end of all clamps (at 7.5, 10, and 15 mmol/L plasma glucose, respectively, 0.65 v 1.43, 1.25 v 2.85, and 2.40 v 4.46 nmol/L each, P less than .05). First-phase plasma C-peptide responses were lower in the athletes at the 10 and 15 mmol clamp levels. The slope of the glucose-C-peptide stimulus-response curve was approximately linear over the range examined, the slope being significantly shallower in athletes than controls for both first phase (P less than .01) and second phase (P less than .01). Plasma insulin responses were similar to C-peptide responses. The attenuation of beta-cell responsiveness over a wide glucose range may be an adaptation to the enhanced peripheral insulin sensitivity seen in athletes.

Adult↗
PubMed2006

Improved perfusion conditions for patch-clamp recordings on human erythrocytes.

Various configurations of the patch-clamp method are powerful tools for examining the transport of charged solutes across biological membranes. Originally developed for the study of relatively large cells which adhere to solid surfaces under in vitro culture, these methods have been increasingly applied to small cells or organelles in suspension. Under these conditions, a number of significant technical problems may arise as a result of the smaller geometry. Here, we examined these problems using human erythrocytes infected with the malaria parasite, Plasmodium falciparum, a system where experimental differences and the technical difficulty of erythrocyte patch-clamp have hindered universal agreement on the properties of the induced ion channels. We found that patch-clamp recordings on infected erythrocytes are especially susceptible to artifacts from mechanical perturbations due to solution flow around the cell. To minimize these artifacts, we designed a new perfusion chamber whose geometry allows controlled solution flow around the fragile erythrocyte. Not only were recordings acquired in this chamber significantly less susceptible to perfusion artifacts, but the chamber permitted rapid and reversible application of known inhibitors with negligible mechanical agitation. Electrophysiological recordings then faithfully reproduced several findings made with more traditional methods. The new perfusion chamber should also be useful for patch-clamp recordings on blood cells, protoplasts, and organelles.

Animals↗
PubMed2004

Possible novel index determined by the glucose clamp test for selection of a suitable therapy for each type 2 diabetic patient.

The hallmark of type 2 diabetes is insulin resistance and insufficient insulin secretion, and appropriate therapy should be selected for each patient. In this study, to establish some index to select suitable therapy for each patient, we evaluated insulin sensitivity and insulin secretion with euglycemic hyperinsulinemic clamp and hyperglycemic clamp tests, respectively, and found that specific GIR index (GIRxIRI (90)) could be a useful marker to select suitable therapy for each type 2 diabetic patient (GIR: glucose infusion rate in euglycemic hyperinsulinemic clamp test; IRI (90): plasma insulin level 90 min after starting the hyperglycemic clamp test).

Blood Glucose↗
PubMed2004

Patch-clamp study of the apical membrane of the midgut of Manduca sexta larvae: direct demonstration of endogenous channels and effect of a Bacillus thuringiensis toxin.

The patch-clamp technique was applied to the apical membrane of epithelial midgut cells of a lepidoptera, Manduca sexta L. Access to the apical membrane, the main target site of Bacillus thuringiensis (Bt) toxins, was achieved by using freshly isolated larval midgut preparations mounted onto holding glass pipettes. The epithelial cells retained their functional integrity, as evidenced by the magnitude of intracellular potentials recorded with microelectrodes. With standard 32 mM K(+) solution in the bath and the patch-clamp pipette, endogenous channel activity was detected in about 50% of experiments, mainly in moulting larvae and larvae that had been kept at reduced temperature for at least two days prior to the experiments. In both cell-attached and inside-out patch-clamp configurations, different types of channel were observed, with conductances varying between about 5 and 50 pS and different conducting properties. Addition of trypsin-activated Cry1Ac Bt toxin in the patch-clamp pipette triggered, after a delay, large conductances of a few nanosiemens. This is the first study allowing exploration, in the intact midgut, of the properties of apical membrane channels and the direct interaction between the apical membrane of epithelial cells and pathogenic agents such as Bt toxins.

Animals↗
PubMed2006

Properties of voltage-gated Na+ channels in the human rhabdomyosarcoma cell-line SJ-RH30: conventional and automated patch clamp analysis.

Conventional and automated patch clamp electrophysiology were used to characterise the Na+ current of the SJ-RH30 human rhabdomyosarcoma. In conventional recordings SJ-RH30 cells exhibited a fast activating, fast inactivating Na+ current at potentials positive to -40 mV; in full current-voltage curves maximum current occurred between -20 and -10 mV. Inactivation kinetics at 0 mV were biexponential with time constants of 0.5 and 3.7 ms. Deinactivation at -90 mV also exhibited two kinetic components. Tetrodotoxin (TTX) blocked the Na+ current completely at 1 microM. The NaV 1.4 selective toxin mu-CTx-GIIIB reversibly blocked the Na+ current approximately 60% at 10 microM. Very similar biophysical behaviour was observed in automated patch clamp and conventional recordings. For example, inactivation mid-point was -72+/-2 mV (slope factor 7.2+/-0.2) in automated patch clamp and -74+/-2 mV (slope factor 7.4+/-0.4) with conventional recording. The corresponding values for activation mid-point were -33.2+/-2.4 and -30.3+/-2.7 mV (slope 5.8+/-0.3 and 6.4+/-0.3, respectively). The throughput of the automated method was used to generate additional pharmacological data on inhibition of the Na+ current. TTX inhibited with an IC50 of 23 nM. Mu-CTx-GIIIB also inhibited the channel in a concentration-dependent manner. Inhibition produced by both tetracaine and amitriptyline were shown to be frequency-dependent. Our experiments indicate that the Na+ current of SJ-RH30 cells arises mainly from channels with a phenotype like recombinant NaV 1.4 channels. The suitability of these cells for automated patch clamp suggests they may be useful for higher throughput studies of the interaction of drugs with human skeletal muscle Na+ channels.

Action Potentials↗
PubMed2002

Ion channels in small cells and subcellular structures can be studied with a smart patch-clamp system.

We have developed a scanning patch-clamp technique that facilitates single-channel recording from small cells and submicron cellular structures that are inaccessible by conventional methods. The scanning patch-clamp technique combines scanning ion conductance microscopy and patch-clamp recording through a single glass nanopipette probe. In this method the nanopipette is first scanned over a cell surface, using current feedback, to obtain a high-resolution topographic image. This same pipette is then used to make the patch-clamp recording. Because image information is obtained via the patch electrode it can be used to position the pipette onto a cell with nanometer precision. The utility of this technique is demonstrated by obtaining ion channel recordings from the top of epithelial microvilli and openings of cardiomyocyte T-tubules. Furthermore, for the first time we have demonstrated that it is possible to record ion channels from very small cells, such as sperm cells, under physiological conditions as well as record from cellular microstructures such as submicron neuronal processes.

Animals↗
PubMed2002

Whole cell patch clamp recording performed on a planar glass chip.

The state of the art technology for the study of ion channels is the patch clamp technique. Ion channels mediate electrical current flow, have crucial roles in cellular physiology, and are important drug targets. The most popular (whole cell) variant of the technique detects the ensemble current over the entire cell membrane. Patch clamping is still a laborious process, requiring a skilled experimenter to micromanipulate a glass pipette under a microscope to record from one cell at a time. Here we report on a planar, microstructured quartz chip for whole cell patch clamp measurements without micromanipulation or visual control. A quartz substrate of 200 microm thickness is perforated by wet etching techniques resulting in apertures with diameters of approximately 1 microm. The apertures replace the tip of glass pipettes commonly used for patch clamp recording. Cells are positioned onto the apertures from suspension by application of suction. Whole cell recordings from different cell types (CHO, N1E-115 neuroblastoma) are performed with microstructured chips studying K(+) channels and voltage gated Ca(2+) channels.

Animals↗
PubMed1999

Series resistance compensation for whole-cell patch-clamp studies using a membrane state estimator.

Whole-cell patch-clamp techniques are widely used to measure membrane currents from isolated cells. While suitable for a broad range of ionic currents, the series resistance (R(s)) of the recording pipette limits the bandwidth of the whole-cell configuration, making it difficult to measure rapid ionic currents. To increase bandwidth, it is necessary to compensate for R(s). Most methods of R(s) compensation become unstable at high bandwidth, making them hard to use. We describe a novel method of R(s) compensation that overcomes the stability limitations of standard designs. This method uses a state estimator, implemented with analog computation, to compute the membrane potential, V(m), which is then used in a feedback loop to implement a voltage clamp; we refer to this as state estimator R(s) compensation. To demonstrate the utility of this approach, we built an amplifier incorporating state estimator R(s) compensation. In benchtop tests, our amplifier showed significantly higher bandwidths and improved stability when compared with a commercially available amplifier. We demonstrated that state estimator R(s) compensation works well in practice by recording voltage-gated Na(+) currents under voltage-clamp conditions from dissociated neonatal rat sympathetic neurons. We conclude that state estimator R(s) compensation should make it easier to measure large rapid ionic currents with whole-cell patch-clamp techniques.

Animals↗
PubMed2003

Endocardial versus epicardial differences in L-type calcium current in canine ventricular myocytes studied by action potential voltage clamp.

OBJECTIVES: The aim of the present study was to assess and compare the dynamics of L-type Ca(2+) current (I(Ca,L)) during physiologic action potential (AP) in canine ventricular cardiomyocytes of epicardial (EPI) and endocardial (ENDO) origin. METHODS: I(Ca,L) was recorded on cells derived from the two regions of the heart using both AP voltage clamp and conventional whole cell voltage clamp techniques. RESULTS: AP voltage clamp experiments revealed that the decay of I(Ca,L) is monotonic during endocardial AP, whereas the current is double-peaked (displaying a second rise) during epicardial AP. The amplitude of the first peak was significantly greater in ENDO (-4.6+/-0.8 pA/pF) than in EPI cells (-2.8+/-0.3 pA/pF). Application of epicardial APs as command pulses to endocardial cells yielded double-peaked I(Ca,L) profiles, and increased the net charge entry carried by I(Ca,L) during the AP from 0.187+/-0.059 to 0.262+/-0.056 pC/pF (n=5, P<0.05). No differences were observed in current densities and inactivation kinetics of I(Ca,L) between EPI and ENDO cells when studied under conventional voltage clamp conditions. Nisoldipine shortened action potentials and eliminated the dome of the epicardial AP. CONCLUSION: I(Ca,L) was shown to partially inactivate before and deactivate during phase-1 repolarization and reopening of these channels is responsible for the formation of the dome in canine EPI cells. The transmural differences in the profile of I(Ca,L) could be well explained with differences in AP configuration.

Action Potentials↗