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At least 505 records · Page 28Linked to original sources
PubMed1980

Differential embryonic cardiovascular responses to acute maternal uterine ischemia: an in vivo microscopic study of rabbit embryos with either intact or clamped umbilical cords.

The effects of acute episodes of maternal uterine ischemia on the cardiovascular system of New Zealand white rabbit embryos were studied by in vivo microscopic methods. On gestational day 12, gravid uteri were surgically externalized, and the walls of the implantation sites were carefully incised and reflected to reveal the embryos. Throughout all procedures, temperature, water, and electrolyte homeostasis were preserved. The embryos within each litter were divided into two groups: 1) two randomly selected embryos whose umbilical cords were clamped, and 2) the remaining embryos of the litter whose umbilical cords were uncompromised. Uterine ischemia was induced by clamping all uterine arterial and venous channels. Occlusion of the maternal uterine vessels produced severe uterine cyanosis within 1-2 min. The embryos whose umbilical cords were not clamped exhibited severe cardiovascular derangements beginning within 3-4 min. In contrast, the embryos whose umbilical cords were clamped (thereby interrupting both umbilical and vitelline circulations) had no observable cardiovascular alterations. The absence of effects in embryos with clamped umbilical cords suggests that acute episodes of hypoxia are well tolerated by young embryos. In contrast, the rapid appearance of cardiovascular derangements after interruption of maternal uterine circulation in embryos with unclamped umbilical cords emphasizes the idea that even brief intervals of uterine ischemia are deleterious to the rabbit embryo.

Animals↗
PubMed2003

Reduction of blood loss during extensive pelvic procedures by aortic clamping--a preliminary report.

OBJECTIVE: The aim was to determine the effect of intraoperative aortic clamping during extensive pelvic procedures on blood loss, operative time, and morbidity. METHODS AND MATERIALS: Thirteen women with ovarian cancer, 1 with cervical cancer, and 1 with an extensive pelvic sarcoma had their aortas completely occluded with a vascular clamp before the pelvic phases of their operations. Heparin and protamine reversal were used. RESULTS: Patients requiring en bloc excision of the internal reproductive organs, pelvic peritoneum, and recto-sigmoid colon in the context of a cytoreductive operation had a median estimated total blood loss of 650 ml (range 200 to 3500), a median of 2 units (range 0 to 8) of blood transfused, and a median total operative time of 155 min (range 90 to 280). There were no complications due to the aortic clamping. CONCLUSION: Most procedures were completed with a less than anticipated blood loss and operative time. Clamping of the aorta may potentially diminish blood loss, operative time, and the incidence of transfusion-related morbidity associated with extensive pelvic operations. Intraoperative aortic clamping merits further investigation.

Adult↗
PubMed1996

The kinetic mechanism of formation of the bacteriophage T4 DNA polymerase sliding clamp.

DNA replication in bacteriophage T4 requires the assembly of a structure called the "sliding clamp" near the 3' end of the DNA strand that is to be extended. This structure is a trimer ring of the T4 gene 45 product (gp45) and serves to regulate the processivity of the DNA polymerase within the T4 DNA replication system. The placement of this ring is performed by an ATPase complex of the products of T4 genes 44 and 62 (gp44/62) that consists of four gp44 subunits and one gp62 subunit. In an effort to understand the role of ATP hydrolysis in processes occurring during the formation of the phage T4 DNA sliding clamp, we have performed direct substrate and product binding experiments and steady-state and presteady kinetic experiments on the gp44/62-gp45 system. Substrate (ATP) and product (ADP) binding studies show that the gp44/62 complex binds 4(+/-1) ATP molecules with a Kd of 34(+/-12) microM, and 3.7(+/-0.3) ADP molecules with a Kd of 14(+/-7) microM. The binding of the other reaction product (inorganic orthophosphate) could not be detected. Presteady-state kinetic analysis of ATP hydrolysis during the sliding-clamp-loading process indicates a biphasic progress curve, consisting of an initial rapid "burst" phase with an amplitude of four ATP molecules per gp44/62 complex and a rate of 15 s(-1), followed by a second slower phase corresponding to the steady-state rate of ATP hydrolysis by this complex. The rate of the burst phase is kinetically consistent with the previously observed rate of T4 DNA polymerase holoenzyme formation. The burst amplitude depends solely on the concentration of gp44/62 ATP binding sites present. These results suggest that the formation of a single T4 sliding clamp requires the hydrolysis of four ATP molecules by one gp44/62 complex in a process requiring 0.5 to 1 second. A model describing the clamp-loading process is discussed in the context of these results.

Adenosine Diphosphate↗
PubMed1994

Voltage clamping of Xenopus laevis oocytes utilizing agarose-cushion electrodes.

Two-electrode voltage clamping of expressed ion channels in intact oocytes of the South African clawed frog Xenopus laevis has been refined to allow stable, low-resistance electrical access to the cytosol (50-800 k omega). Glass microelectrodes were filled with a cushion of 1% agarose at their tips to prevent KCl leakage (agarose-cushion electrodes). Insertion of these electrodes into X. laevis oocytes yielded stable preparations for periods of more than 1 h with a stable input resistance of 1-4 M omega. Furthermore, a simple modification of the voltage-clamp circuit (charging compensator) is described that increases the flexibility of arrangements for differential recording of the membrane potential in order to subtract voltage drops across a series resistance. The result is a considerable increase in the practically attainable speed of the voltage clamp with the conventional two-electrode arrangement. The performance of the charging compensator was tested on an equivalent circuit that simulates the oocyte and electrodes. In addition, the combination of agarose-cushion electrodes and the charging compensator was tested on oocytes expressing Shaker H4 currents. The fidelity of the voltage-clamp circuit was also verified by measuring the membrane potential with additional independent microelectrodes connected to a differential amplifier, independent of the two-electrode voltage clamp system. The system described here will be useful for ion channel studies in X. laevis oocytes requiring long-term recordings and/or measurements of large, fast ion currents.

Animals↗
PubMed1981

Structural responses to voltage-clamping in the toad urinary bladder. I. The principal role of granular cells in the active transport of sodium.

The structural consequences of clamping the transepithelial potential difference across the toad's urinary bladder have been examined. Reducing the potential to zero (short-circuiting) produced no apparent changes in the morphology of any of the four cell types which comprise the epithelium. Computer assisted, morphometric analysis of quick frozen specimens revealed no measurable difference in granular cell volume between open-and short-circuited preparations. However, when the open-circuit potential was quantitatively reversed (serosa negative with respect to mucosa), some of the preparations showed a marked increase in granular cell volume. To examine this more systematically twelve preparations were voltage-clamped at 50 mV (serosa negative); eight of the twelve revealed prominent granular cell swelling relative to control, short-circuited preparations. Only in this group of eight had the external circuit current fallen substantially during the clamping interval. Mitochondria-rich cells were not affected detectably. Application of the diuretic amiloride prior to clamping at reversed potential prevented granular cell swelling in every case. Goblet cells which were often affected by the - 50 mV clamp were not protected by the diuretic. Granular cell swelling thus appeared to be dependent on sodium entry at the mucosal surface. We also observed that, after voltage reversal, the apical "tight" junctions of the bladders were blistered as they are with hypertonic mucosal media. This blistering was associated with an increase in passive ionic permeability and was not prevented by application of amiloride. This finding is consistent with the evidence that the junction is a complex barrier with asymetric, and hence, rectifying properties for intrinsic ionic conductance as well as hydraulic permeability. These findings, together with others from the literature, lead to the conclusion that the granular cells constitute the principal, if not sole, elements for active sodium transport across toad urinary bladder and that they swell when sodium entry exceeds the transport capacity of the pump at the basal-lateral surface.

Amiloride↗
PubMedDate not supplied

Glucose-clamp by artificial pancreas in the study and management of a patient with insulinoma.

Four euglycemic glucose-clamp studies by artificial pancreas (Biostator, Miles) have been performed during prolonged fast before and after pharmacological treatment in a patient with insulinoma. In the basal state a high glucose infusion rate (8.9 g/h) was unable to achieve the preselected blood glucose plateau of 80 mg/100 ml. The plasma insulin levels during this first glucose-clamp were comprised between 18 and 50 microunits/ml. On the first day of diazoxide treatment (300 mg/die),. the glucose infusion rate decreased to 6.4 g/h, without variation in plasma insulin level, thus suggesting a diazoxide effect independent of the inhibition of insulin secretion. After 7 days of diazoxide treatment, a further reduction of glucose infusion (5.8 g/h), together with a lowering of plasma insulin levels (7-18 microunits/ml) was observed. Both in the basal state and during diazoxide treatment a circadian pattern of glucose requirement was noted, with lower glucose need and plasma insulin levels during the night. Surgery was undertaken with glucose-clamp by artificial pancreas; blood glucose level being higher than the preselected value of 80 mg/100 ml, simple monitoring of glycemia was performed. The excision of a single adenoma was followed by a substantial rise in blood glucose 20 min later. An additional glucose-clamp, performed 3 months after surgery showed a dramatic fall of the glucose infusion rate (2.9 g/h) needed to achieve the preselected blood glucose plateau, confirming the completeness of the intervention. This experience shows that glucose-clamp by artificial pancreas may be of great value in the study as well as in the pharmacological and surgical treatment of patients with insulinoma.

Adenoma, Islet Cell↗
PubMed1984

A newly designed clamp facilitates hepatic resection.

We designed a new clamp (Inokuchi liver clamp), mainly used for partial or wedge resection of the liver. This clamp is gently curved and has 9 non-traumatic teeth with double step locking devices at the tips. This clamp proved to be most useful for limited hepatic resection, a common procedure for primary liver cancer associated with cirrhosis, however, it can also be used for major resections. From August 1981 to February 1984, this clamp was used by our surgical team in 45 resections of the liver for primary and secondary malignant tumors and benign hemangiomas.

Constriction↗
PubMed2004

Postoperative renal function after elective abdominal aortic aneurysm repair requiring suprarenal aortic cross-clamping.

PURPOSE: To examine postoperative renal function after suprarenal aortic cross-clamping performed without renal hypothermia in patients undergoing elective abdominal aortic aneurysm (AAA) surgery. METHODS: Between 1991 and 2000, 18 patients underwent surgery for a juxtarenal AAA, which required a suprarenal aortic cross-clamp. All AAAs were repaired with a proximal anastomosis just below the renal arteries. We divided the patients into two groups according to the duration of the renal ischemia: <45 min (n = 12) and > or =45 min (n = 6). The postoperative changes in renal function were analyzed. RESULTS: There were no hospital deaths and none of the patients needed permanent hemodialysis. The postoperative peak in the serum creatinine level after suprarenal cross-clamping for > or =45 min was significantly higher than that after cross-clamping for <45 min. The percentage changes in serum creatinine and blood urea nitrogen were correlated positively with the duration of renal ischemia, and were significantly greater in the group with renal ischemia of <45 min than in the group with prolonged renal ischemia (> or =45 min). CONCLUSIONS: Suprarenal aortic cross-clamp without performing renal hypothermia is safe and able to be tolerated well by the patient during elective AAA surgery, although careful attention must be paid to limiting the period of renal ischemia.

Acute Kidney Injury↗
PubMed2002

Biochemical alterations in cerebrospinal fluid during thoracoabdominal aortic cross-clamping in dogs.

Spinal cord damage during and after thoracoabdominal aortic cross-clamping continues to be a major problem. Somatosensory and motor evoked potentials have been used to monitor spinal cord function but their value for predicting paraplegia has been controversial. The aim of this study was to measure biochemical markers in the cerebrospinal fluid (CSF) and correlate changes with spinal cord ischemia. Since neural tissue utilizes only glucose as substrate for its metabolism and energy supply, we measured changes of metabolites of anaerobe glycolysis. In a canine model in which general anesthesia was used, the thoracoabdominal aorta was cross-clamped proximally and distally for 60 min. Hemodynamic parameters, blood gases, and glucose level were monitored continuously. Blood and CSF sampling were performed at baseline, at 15, 30, and 55 min during cross-clamping, and at 5 and 15 min after aortic declamping. Levels of lactate (1.7 +/- 0.1 to 3.2 +/- 0.3 mmol/L), pCO2 (43 +/- 2 to 35 +/- 1.6 mmHg), and neuron-specific enolase (NSE) (5.17 +/- 0.5 to 13.0 +/- 3.5 mg/L) in CSF showed significant changes (p < 0.05) during clamping and reperfusion. Changes in CSF lactate and NSE levels correlate with the duration of spinal cord ischemia. These markers of ischemic metabolism appear suitable to monitor the degree of spinal cord ischemia during thoracoabdominal cross-clamping and may be useful to predict the efficacy of preventive methods.

Animals↗
PubMed1990

Cerebrospinal fluid drainage and steroids provide better spinal cord protection during aortic cross-clamping than does either treatment alone.

We investigated whether intravenous methylprednisolone (30 mg/kg) before 30 minutes of aortic cross-clamping and after 4 hours could enhance the effects of cerebrospinal fluid drainage on spinal cord perfusion pressure and postoperative paraplegia when proximal blood pressure was controlled with sodium nitroprusside and partial exsanguination. Dogs were randomized into three groups: group 1 (n = 6), control; group 2 (n = 7), steroids; and group 3 (n = 6), steroids with cerebrospinal fluid drainage. During aortic cross-clamping, blood pressure proximal to the clamp decreased significantly in each group compared with baseline (p less than 0.05), but did not differ among groups (group 1 = 82.2, group 2 = 82.1, group 3 = 86.6 mm Hg, p greater than 0.05). Mean distal pressure decreased from systemic values to 8.4, 8.5, and 3.7 mm Hg, respectively, after aortic cross-clamping (p less than 0.05); these values did not differ from one another (p greater than 0.05). During aortic cross-clamping, cerebrospinal fluid pressure in groups 1 and 2 did not differ significantly compared with baseline (12.2 versus 8.2, 14.2 versus 10.7 mm Hg, p greater than 0.05), whereas in group 3 the baseline cerebral spinal fluid pressure of 10.7 mm Hg decreased to 0.4 mm Hg (p less than 0.05). Spinal cord perfusion pressure in group 3 was significantly higher than in groups 1 and 2 (3.3 versus -3.9 and -5.7 mm Hg, p less than 0.05), but did not differ between groups 1 and 2 (p greater than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1984

Analysis of EEG changes with carotid clamping by selective analog filtering, matched inverse digital filtering and automatic adaptive segmentation: a comparative study.

A comparative evaluation was made of 3 methods for possible use in a system for automatic evaluation and signaling of significant EEG changes associated with carotid clamping. The methods were: (1) selective analog filtering in two frequency bands ("fast'--4-20 c/sec; and "slow'--0.8-1.0 c/sec); (2) inverse digital filtering, a computer-based method in which a filter is formed from a pre-clamping EEG baseline such that only frequency components different from the baseline components appear in the filter output; and (3) automatic adaptive segmentation, a computer-based method of detecting and signaling EEG changes by comparison of the autocorrelogram of a pre-clamping reference sample with that from an equal-duration sample "seen' through a progressively moving window in the post-clamping period. For the analyses, portions of ink-recorded monitoring EEGs previously interpreted as showing changes consequent to carotid clamping were transferred to a cassette tape recorder system by means of a multichannel photo-optical scanning system. Of the 3 methods, automatic adaptive segmentation was clearly the best. For selective analog filtering, the thresholds for a significant change were difficult to set. Inverse digital filtering was unsatisfactory because of its insensitivity to changes in the amplitude frequency components already present, although new frequency components could be detected. An incidental finding was that a slow-speed write-out of the analog filter outputs provided a good visual indication of EEG changes.

Brain↗
PubMed1984

Effect of descending thoracic aorta clamping and unclamping on phasic coronary blood flow.

Myocardial infarctions during aortic surgery often occur after aortic clamping and unclamping. In order to investigate the aortic blood pressure (AoBP)-coronary blood flow (CBF) relationship, hemodynamic parameters and phasic circumflex CBF in 15 anesthetized and open-chest dogs during clamping and unclamping of the thoracic descending aorta have been recorded. During clamping, mean aortic blood pressure (MAoBP) rose from 97 + 17 to 150 + 42 mm Hg (P less than 0.001), and total combined left-ventricular power (Wtc) from 692 + 232 to 923 + 402 mW (P less than 0.001) while the ascending aortic blood flow (AoBF) and heart rate did not change significantly. The mean circumflex blood flow (MCBF) increased from 67 + 30 to 88 + 30 ml/min. The increase in systolic coronary blood flow (+73%) was larger than that in diastolic coronary blood flow (DCBF) (19%). The late coronary resistances were increased 39%. Conversely, after unclamping, MAoBP decreased while AoBF and Wtc increased. During the first cardiac cycles after aortic unclamping DCBF decreased 50% with a decrease in the diastolic blood pressure (DBP). Four cycles later, DCBF reincreased while DBP kept on decreasing. This may be related to an active coronary vasodilatation. A linear relationship between DCBF and DBP has been obtained during acute change in DBP due to clamping or unclamping. From these linear relationships, the change in diastolic zero flow pressure (PfO) has been found to be about + 40 mm Hg during clamping. This change in PfO may be responsible for the observed large fall in DCBF during unclamping. The decrease in DCBF associated with the increase in Wtc accounts for the delayed active vasodilatation.

Animals↗
PubMed1993

Estimation of the steady-state characteristics of the Hodgkin-Huxley model from voltage-clamp data.

In a companion paper in this issue we show that all the parameters and functions of the Hodgkin-Huxley (HH) model can be calculated in a unique and optimal manner from voltage-clamp peak current data when the steady-state activation (x infinite) and inactivation (z infinite) characteristics are known. Assuming that x infinite and z infinite can be adequately expressed by a Boltzmann equation with two parameters, the present paper describes an optimization procedure to estimate these parameters from peak current data without any constraint on the time constants of activation and inactivation. The required voltage-clamp data are the peak ionic current value (Ip) and its time of occurrence (tp), as provided by two complementary voltage-clamp protocols involving, in each case, a single fixed value of clamp potential. The performance of the procedure was very good with simulated medium- or high-resolution data as it was then possible to determine with confidence the degrees of the gating variables. The performance was also very good with low-resolution data, provided that the degrees of the gating variables were chosen correctly. Good results were also obtained in the presence of Gaussian noise. On the other hand, estimates of x infinite and z infinite based on normalization of peak current measurements always give uncertain results that are likely to be incorrect in a number of circumstances. It is concluded that the HH model can be a useful tool for the interpretation of voltage-clamp peak current data when a reasonable database is available.

Animals↗
PubMed1980

Design of a single electrode voltage clamp.

The detailed schematic diagrams and construction techniques are presented for a single microelectrode voltage clamp. The devices is used to study the membrane processes of small cells not able to be penetrated with the traditional two microelectrode system. The technique utilizes the same microelectrode alternately for current injection and membrane potential sampling on a time-sharing basis controlled by electronic switching circuitry. Current is injected in pulses and the membrane potential is sampled after an individual current pulse discharges from the microelectrode capacitance to the true membrane potential. The device can either measure the voltage response to an injected current waveform (current injection mode) or the membrane currents generated during a controlled change in membrane potential (voltage clamp mode). In voltage clamp mode, the membrane potential reaches steady-state within 2 msec (maximum time) in response to a 40 mV step command. The single electrode voltage clamp is potentially very important to the investigation of slow current processes within electrically excitable cells too small to be previously studied with traditional voltage clamp technology.

Animals↗
PubMed1990

High resolution recording of asymmetry currents from the squid giant axon: technical aspects of voltage clamp design.

The design, realisation and performance of a voltage clamp system dedicated to recording asymmetry currents from the squid giant axon is presented. The design has been optimised with respect to dynamic response, signal-to-noise ratio and linearity. Analytical expressions are given for both the dynamic performance and noise characteristics which simplify the design and setting up of the clamp and provide excellent agreement between design theory and practice. A 0.5 cm2 area of membrane can be voltage clamped in response to a command input voltage step within 10 microseconds with smooth settling and up to 100% of the effective series resistance being compensated. The noise contributions of the recording chamber, voltage sensing electrodes and clamp electronics have been reduced such that recording of gating currents with a more than 10-fold reduction in the number of averages required compared with previous clamp designs is possible. The overall system nonlinearity results in typically less than 1% contribution to the measured asymmetry charge.

Animals↗
PubMed1993

A new configuration for voltage clamp of axons used to demonstrate nerve conduction blockade by a 2,5-disubstituted pyrrolidine.

An original voltage-clamp technique on axons from crayfish Procambarus clarkii is described in this paper. Its advantages are: a fast dissection leading to the availability of several fibers of different diameters (10-500 microns) that may contain different ion channels; and use of a double-electrode voltage clamp on a chosen fiber with good clamping characteristics (short time clamp and good space clamp, small leak conductance). Because of the absence of exogenous lipidic phase in the superfusion chamber, this technique appears particularly suited to studying how liposoluble neurotoxins affect nerve conduction. This method has been successfully applied to test the effect of a synthetic derivative (2-(1non-8enyl)-5(1non-8enyl)pyrrolidine (Pyr 9)) of ant venom alkaloids from Monomorium species on nerve conduction. We present here evidence of a strong blocking effect on inward current involved in spike conduction. The resting potential of the treated axons did not change and it appears that only the inward current was affected.

Animals↗
PubMed1993

The immobility response elicited by clamping, bandaging and grasping in the Mongolian gerbil (Meriones unguiculatus).

When grasped by the skin of the nape and lifted into the air, the young of many altricial mammals exhibit an immobility response in which they tuck their limbs against their bodies and remain inert. Such a response can be induced in the adults of some species, especially if a stronger tactile stimulus such as bandaging the head and neck or clamping the skin of the nape, is applied. In this study, the immobility response of the Mongolian gerbil (Meriones unguiculatus) is investigated, which appears to differ in potentially useful ways from other commonly studied species such as rats (Rattus norvegicus). It has been previously reported that for rats clamping or bandaging had a more profound effect on the immobility response than grasping. Mongolian gerbils were tested with all three methods (grasping, bandaging and clamping), which were repeated at intertrial intervals ranging from 3 h to 40 days. Grasping induced a significantly longer duration of immobility than either bandaging or clamping. However, repeated trials significantly increased the duration of immobility induced by clamping, whereas repeated grasping or bandaging did not do so. The marked difference in the induction of the immobility response in gerbils as compared to rats, may provide a useful model for the study of this behavior.

Animals↗
PubMed1986

Synaptic currents at interpositorubral and corticorubral excitatory synapses measured by a new iterative single-electrode voltage-clamp method.

A new iterative single-electrode voltage clamp method was applied to the measurement of synaptic currents in the red nucleus (RN) neuron of the cat. Voltage clamp was attained within 10 repetitions with great stability and the new algorithm was demonstrated to be superior to the original algorithm of iterative voltage clamp. With a conventional microelectrode, it was possible to measure the synaptic current with the time resolution of 50 microseconds. The synaptic currents evoked by stimulation of the contralateral interpositus nucleus (IP) had time-to-peak ranging from 200 to 540 microseconds and fitted well to alpha functions. Corticorubral (CR) synaptic current was also measured by making use of synaptic plasticity. The stimulation of the ipsilateral cerebral peduncle in cats with chronic lesion of the contralateral IP evoked fast rising EPSPs, as reported previously. The CR-EPSPs with times-to-peak less than 1 ms were subjected to voltage clamp. The CR synaptic currents had times-to-peak ranging from 350 to 880 microseconds. Since most of the interpositorubral (IR) synapses and a part of the CR synapses in IP-lesioned cats are situated on the somatic membrane of RN neurons and some of the CR synaptic currents were as rapid as the IR synaptic currents, the observed synaptic currents evoked by stimulation of the IP and those of the fast-rising CR-EPSPs were taken to originate from the synaptic membrane under space-clamp, i.e. soma. The present study provided additional evidence for the sprouting of the CR fibers as well as the time course of the synaptic current at the dendritic synapses remote from the soma, for the first time.

Animals↗