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At least 1,063 records · Page 59Linked to original sources
PubMed1987

Voltage clamp analysis of lamprey neurons--role of N-methyl-D-aspartate receptors in fictive locomotion.

Spinal neurons in the lamprey have been subjected to a voltage clamp analysis of the excitatory currents generated during fictive locomotion with particular reference to the phasic activation of voltage dependent N-methyl-D-aspartate (NMDA) receptors. Voltage-clamped neurons observed during NMDA-induced fictive swimming show excitatory and inhibitory synaptic currents in phase with the ipsilateral and contralateral ventral root discharges, respectively. The excitatory synaptic currents showed a marked voltage dependence suggesting that potential sensitive conductances such as the NMDA ionophore are involved in the synaptic events underlying rhythmic locomotor activity. The effect of NMDA receptor activation during application of tetrodotoxin has also been analyzed during NMDA-induced pacemaker-like oscillations. Such NMDA-induced oscillations are essentially abolished during the voltage clamp. In the presence of NMDA current voltage plots reveal a negative slope conductance in the potential range of the inherent oscillations. The addition of tetraethyl ammonium (TEA) to NMDA solution enhanced a net steady state inward current by more than 10-fold due to a partial block of the outward currents. A kinetic analysis was done with a frequency domain technique using a white noise stimulus to linearly perturb the membrane potential over a wide range of frequencies. The analysis revealed that the induced negative conductance leads to a response which is nearly 180 degrees out of phase with the stimulus at low frequencies. This is an unstable condition which leads to the depolarizing phase of the induced oscillations.

Action Potentials↗
PubMed1988

Voltage- and current-clamp recordings of the receptor potential in mouse taste cell.

Intracellular recordings were obtained using the current-clamp and voltage-clamp techniques. When the taste cell membrane was voltage-clamped, the sucrose stimulus induced an inward current accompanied by a membrane resistance increase while the NaCl stimulus induced an inward current accompanied by a membrane resistance decrease. These phenomena indicated that sucrose and NaCl have quite a different generation mechanism of taste responses.

Animals↗
PubMed1989

Ionic currents on type-I cells of the rabbit carotid body measured by voltage-clamp experiments and the effect of hypoxia.

Type-I cells (from rabbit embryos) in primary culture were studied in voltage-clamp experiments using the whole cell arrangement of the patch-clamp technique. With a pipette solution containing 130 mM K+ and 3 mM Mg-ATP, large outward currents were obtained positive to a threshold of about -30 mV by clamping cells from -50 mV to different test pulses (-80 to 50 mV). Negative to -30 mV, the slope conductance was low (outward rectification). The outward currents were blocked by external Cs+ (5 mM) and partially blocked by TEA (5 mM) and Co2+ (1 mM). The initial part of the outward currents during depolarizing voltage pulses exhibited a transient Ca2+ inward component partially superimposed to a Ca2+-dependent outward current. Inward currents were further characterized by replacing K+ with Cs+ in the intra- and extracellular solution in order to minimize the outward component and by using 1.8 mM Ca2+, 10.8 mM Ca2+ or 10.8 mM Ba2+ as charge carrier. Slow-inactivating inward currents were recorded at test potentials ranging from -50 to 40 mV (holding potential -80 mV). The maximal amplitude, measured at 10 mV in the U-shaped I-V curve, amounted to 247 +/- 103 pA (n = 3). This inward current was insensitive to 3 microM TTX, but blocked by 1 mM Co2+ and partially reduced by 10 microM D600 and 3 microM PN 200-100. In contrast to outward currents, the inward currents exhibited a 'run-down' within about 10 min. Lowering the pO2 from the control of 150 Torr (air-gassed medium) to 28 Torr had no apparent effect on inward currents, but depressed reversibly outward currents by 28%. In conclusion, it is suggested that type-I cells possess voltage-activated K+ and Ca2+ channels which might be essential for chemoreception in the carotid body.

Adenosine Triphosphate↗
PubMed1990

Whole-cell voltage-clamp study of sodium current in neuroblastoma cells: effects of inhibition of neurite outgrowth by colchicine.

A method is described for the production of large numbers of neurite-free neuroblastoma cells that are especially suitable for studies involving whole-cell voltage clamp. Differentiation in the presence of colchicine yielded cells having abundant sodium channels, highly reproducible peak currents and no space-clamp problems. Treatment with this drug did not alter the electrophysiological properties of the cells. Colchicine might be similarly advantageous in voltage-clamp studies of different ion channels and other types of cultured neurons.

Axons↗
PubMed1993

Mechanisms of anoxia-induced depolarization in brainstem neurons: in vitro current and voltage clamp studies in the adult rat.

To determine the mechanisms underlying the depolarization induced by anoxia in brainstem neurons, we studied single neurons in brainstem slices using conventional micro-electrodes and freshly dissociated hypoglossal and vagal cells using patch clamp techniques (whole-cell configuration). Since glutamate concentration increases in the extracellular space during O2 deprivation, we first tested whether N-methyl-D-aspartate (NMDA) and non-NMDA receptors are involved in this anoxia-induced depolarization. APV, MK-801, CNQX and KYN (NMDA and non-NMDA blockers), which bathed slices after control anoxia runs, did not affect the depolarization trajectory. Decreasing extracellular Na+ (Nao+) from 150 mM to 5 mM attenuated markedly and significantly the depolarization observed during anoxia (15-20% of control). The relation between intracellular adenosine triphosphate (ATP) and the anoxia-induced depolarization was also investigated in the slice and in dissociated single brainstem neurons. In the slice, iontophoresis of ATP did not give consistent results. Since we could not ascertain that ATP was actually iontophoresed through high resistance (50-80 M omega) microelectrodes, we patched single neurons and studied the effect of clamping intracellular ATP levels on the hyperpolarizing holding current (IH) in the voltage clamp mode. The increase in IH with anoxia (or cyanide) was markedly attenuated in cells patched with pipettes containing ATP. We conclude that in brainstem neurons, the anoxia-induced depolarization: (a) is not a function of an increase in extracellular glutamate concentration; and (b) depends on Na+ and ATP-mediated processes.

6-Cyano-7-nitroquinoxaline-2,3-dione↗
PubMed1994

Electrical coupling between cultured glomus cells of the rat carotid body: observations with current and voltage clamping.

Electrically coupled pairs of cultured rat glomus cells were used. In one group of experiments, both cells were current-clamped. Delivery of positive or negative pulses to Cell 1 elicited appreciable voltage noise in this cell and large action potentials (probably Ca2+ spikes) in about 10% of them. Both passive and active electrical events spread to Cell 2, presumably through the gap junctions between them. The coupling coefficient (Kc) was larger for the spikes than for non-regenerative voltage noise. In another group of experiments, Cell 1 was current-clamped and Cell 2 was voltage-clamped at Cell 1 EM. Pulses of either polarity, delivered to Cell 1, produced current flow through the intercellular junction and allowed direct measurements of junctional currents (Ij) and total conductances (Gj). Ij had a mean value of about 12.5 pA and Gj of 391 pS. Unitary (presumably single channel) conductance (gj) was about 78 pS.

Action Potentials↗
PubMed1987

Ontogeny of immobility reactions elicited by clamping, bandaging, and maternal transports in rats.

Wistar neonate rats assume a characteristic posture when being transported by the mother. This carrying posture is normally elicited by the pressure given by the mother's teeth on the pup's neck. By clamping or bandaging the neck and head an immobility reflex with flexion of body and limbs resembling the carrying posture is elicited when pups are in a supine position. On the contrary, by bandaging or by lightly clamping the pups in a prone position, a dorsiflexion with extension of forelimbs is elicited. Both clamping or bandaging inhibits contact and air righting. After a period of immobility bursts of activity follow. The characteristics of all the reactions described above depend on the age of the developing pups. It seems that the immobility reflex with ventroflexion of the body is a behavior used initially by pups to facilitate carrying by the mother, and by both pups and adults as a defense against predators. The posture adopted by the pups bandaged in the neck in a prone position is very similar to the posture they adopt while suckling from the mother. It is postulated that the weight of the mother when lying over the pups plus the pressure on the paws caused by their prone position, could be the stimulus that normally produces the suckling posture.

Aging↗
PubMed1996

The pelvic C-clamp for the emergency treatment of unstable pelvic ring injuries. A report on clinical experience of 30 cases.

An unstable pelvic ring injury was stabilized with the AO C-clamp in thirty multiply injured patients. The average ISS was 29 (19-57). Transfusions totalled 24 units of blood/fresh frozen plasma/platelets (0-117) on average. In 12 cases, the application was for an unstable fracture alone, in 18 patients there was an unstable haemodynamic situation in addition. The application was haemodynamically effective in 10 cases. In 66% of cases, the initial reduction was good and the anatomy of the pelvic ring was adequately restored. Ten patients (33%) died; five during the first hours after admission due to haemorrhagic shock; the remaining five from multiple organ failure, fat embolism and head injury. Definitive stabilization was accomplished after 4.5 days on average (0-15). Complications relating directly to the clamp did not occur. The application of the C-clamp has a clear place in the management of polytraumatized patients with linear unstable pelvic ring injuries.

Adolescent↗
PubMed1984

A new clamping and stretching procedure for determination of collagen fiber stiffness and strength relations upon maturation.

Clamping of tendon fibers is a major concern in connective tissue biomechanics. We present here a new clamping method. Also the stretching procedure is different from the conventional extension until the point of failure. Thus we have used a procedure of interval stretches, where 0.01 extensions during 2.5 s are succeeded by periods of relaxation. This procedure reduces the stress on clamps and transducers which causes serious problems in conventional extensions of some older specimen. The influence of stretching rate and periods of relaxation on the observed values of stiffness has been tested and discussed. The fibers from rat tail tendons only show a minor increase in stiffness between 40 day and 90 day old animals, and do not show significant changes from the age of 90 to 240 days. The values of stiffness expressed as Young's modulus of elasticity, had maximal values of 1.2, 1.8 and 1.9 kNmm-2 at the three ages investigated. The fiber strength, however, increases dramatically, thus the ultimate value was 18 Nmm-2 for 40 day old fibers, while at 90 days and 240 days it had increased to 102 Nmm-2 and to 106 Nmm-2, respectively.

Age Factors↗
PubMed1992

A multimodality approach lengthens warm ischemic time during aortic cross-clamping.

To evaluate the effects of exsanguination, cerebrospinal fluid drainage (CSFD), steroids alone and in conjunction with CSFD on spinal cord perfusion pressure (SCPP), and neurological outcome following 70 min of normothermic spinal cord ischemia, we monitored proximal (Px BP) and distal (Ds BP) aortic blood pressure, cerebrospinal fluid pressure, and somatosensory evoked potentials (SEP) in 29 mongrel dogs. In all animals Px BP during aortic cross-clamping was controlled with partial exsanguination (40-50% circulating blood volume). Dogs were randomized into four groups (gp): gp 1 (n = 6) control; gp 2 (n = 8) steroids only (methylprednisolone 30 mg/Kg 10 min before aortic occlusion and 4 hr later); gp 3 (n = 8) CSFD only; gp 4 (n = 7) steroids and CSFD. Partial exsanguination effectively controlled Px BP during aortic cross-clamping in all groups. After the statistically significant decrease from preclamp values, mean Px BP did not differ among groups (78.9, 81.2, 80.5, and 80.3 mm Hg, respectively, P greater than 0.05). Mean Ds BP decreased from systemic values to 12.6, 16.8, 16.7, and 17 mm Hg, respectively, after aortic occlusion (P less than 0.05); these values did not differ from one another. CSFP did not change significantly from its baseline value while the aorta was cross-clamped in gp 1; CSFP was significantly reduced to 6.2 mm Hg in gp 2, steroid-treated animals (P less than 0.05 vs gp 1); a further significant reduction in CSFP was noted in gp 3 and 4 undergoing CSFD (0.07 and 0.67 mm Hg, respectively, P less than 0.05 vs gp 1 and 2).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

On the interpretation of voltage-clamp data using the Hodgkin-Huxley model.

This paper describes a method to extract membrane model parameters from experimental voltage-clamp records. The underlying theory is based on two premises: (1) the membrane dynamics can be described by a Hodgkin-Huxley (HH) model, and (2) the most reliable data provided by voltage clamp experiments are peak current (Ip) measurements. First, the steady-state characteristics of activation (x infinity) and inactivation (z infinity) must be estimated, and it is shown that Ip data provided by standard voltage-clamp stimulation protocols are sufficient for this purpose for the case of well-separated activation (tau x) and inactivation (tau z) time constants, tau x << tau z. Next, we propose a test (R test) to establish the suitability of the HH model to represent the data. When the HH model is applicable (successful R test), the procedure yields the degree of the gating variables, a range of maximum membrane conductance (g) values, and a tau x/tau z ratio that relates x infinity and z infinity to the Ip data. When additional information is available, such as the time of occurrence of Ip or an estimate of tau z from the late portion of the ionic current response, one can narrow down the value of g and estimate all the HH parameters and functions. Otherwise, when the R test is not successful, one can conclude that x infinity and z infinity have been incorrectly estimated because tau x and tau z are not sufficiently separated or that the HH model is not applicable to the data.

Algorithms↗
PubMed1975

The development of a glucose clamp.

A reliable control system was developed for clamping (i.e., holding at a steady level) the concentration of blood glucose in the hyperglycemic region of a normal nonanesthetized dog. The system is based upon, and hence largely validates, a mathematical model of the canine glucoregulatory mechanism which was assembled from the results of experiments in which radioisotopes were used. The operation of the clamp, however, does not require the use of radioisotopes. The glucose clamp is a tool which may be applicable clinically in the measurement of glucose turnover and in the laboratory in the study of the effects of glucose turnover of variable insulin with constant glucose levels.

Animals↗
PubMed1980

Measurement of euglobulin fibrinolysis time in women with retarded fetal development. The effect of the clamping and step tests on plasminogen activator activity.

The effects of two experimental stimuli, clamping of the cubital vein and exercise (step test), on the euglobulin lysis time of women with retarded fetal development (92 cases), with physiologic pregnancy (50 cases) and non-pregnant women (20 cases) were studied. Both tests resulted in a pronounced shortening of euglobulin lysis time in the non-pregnant and to a lesser extent in the physiologic pregnancy cases (statistically significant after clamping of the cubital vein, statistically insignificant after the step test). In the etiologically heterogeneous group of pregnancy with retarded fetal development the response to both stimuli was weaker in comparison with the normal pregnancy group, and in many cases (58.7%) even "paradoxical", that is, instead of a rise in fibrinolytic activity, a fall was observed. These results indicate that in women with retarded fetal development fibrinolytic activity of the blood doses not rise as readily as it does in normal pregnancies. This applies both to local response (clamping test) and systemic response (step test), and is probably due to a fall in the plasminogen activator content of the venous vessel walls. As a working hypothesis, it is presumed that insufficiency of the plasminogen activator activity system facilitates the accumulation of fibrin deposits in the uterine--placental blood circulation, and contributes to retardation of intrauterine fetal growth.

Exercise Test↗
PubMed1975

Application of a lateral compression clamp in the management of mandibular fractures.

A lateral compression clamp system has been used in the treatment of fractures of the mandible. It provides rigid fixation and promotes earlier osteogenesis at the fracture site. Intermaxillary fixation can often be eliminated in edentulous persons and greatly reduced in duration when necessary as an adjunct to fixation in patients with teeth. These significant qualities make the compression clamp quite beneficial in the treatment plan and postoperative management of many otherwise difficult cases. Having evaluated our experiences with compression clamps, we believe that this approach deserves further attention and may contribute to a solution of the controversy that often exists regarding the management of mandibular fractures in both edentulous patients and those with a compromised complement of teeth.

Accidents, Traffic↗
PubMed1996

Saturation revealed by clamping the gain of the retinal light response.

The saturation nonlinearity of the retinal light response in human was measured by a psychophysical technique in which the adaptive gain control mechanism was clamped by the presence of a fixed surround in a small (7') foveal test field. Gain clamping was established by showing that the normal variation in temporal summation properties with test intensity was abolished in the gain clamping paradigm. The static saturation function constructed from the increment/decrement asymmetries around a range of base intensities was shown to conform more closely to the Naka-Rushton hyperbolic saturation equation than to three other candidate nonlinearities.

Adaptation, Ocular↗
PubMed1992

The capture of a DNA double helix by an ATP-dependent protein clamp: a key step in DNA transport by type II DNA topoisomerases.

The binding of linear and circular forms of DNA to yeast DNA topoisomerase II or its complex with AMPPNP, the nonhydrolyzable beta,gamma-imido analog of ATP, was carried out to probe the ATP analog-induced conformational change of the enzyme. Binding of the ATP analog is shown to convert the enzyme to a circular clamp with an annulet, through which only a linear DNA can pass; subsequent circularization of the bound linear DNA forms a salt-stable catenane between the protein circular clamp and the DNA ring. Analysis of catenane formation between a small DNA ring originally bound to the topoisomerase and a large DNA ring subsequently added, under conditions such that the two do not exchange, supports a model in which a second DNA double-helix can enter the open jaws of a DNA-bound protein clamp, and the closure of the jaws upon ATP-binding traps the second duplex and transports it through an enzyme-operated gate in the first DNA duplex.

Adenosine Triphosphatases↗
PubMed1989

A monolithic patch-clamping amplifier with capacitive feedback.

Patch-clamping is an established method for directly measuring ionic transport through cellular membranes with sufficient resolution to observe open/close transitions of individual channel molecules. This paper describes an alternative technique for patch-clamping which uses a capacitor as the transimpedance element. This approach eliminates bandwidth and saturation limitations experienced with resistive patch-clamping amplifiers. A complete monolithic design featuring an on-chip operational amplifier, a capacitor array with gain-ranging from 30 pF down to 0.03 pF, and reset and gain ranging switches has been fabricated using 5 microns CMOS technology. It is shown that the voltage noise of the CMOS operational amplifier limits the overall noise performance, but that performance competitive with conventional instruments can be achieved over a 10 kHz bandwidth, at least for small input capacitances (less than or equal to 5 pF). Results are presented along with an analysis and comparison of noise performance using both resistive and capacitive elements.

Amplifiers, Electronic↗
PubMed1993

Pressure-clamp technique for measurement of the relaxation kinetics of mechanosensitive channels.

The pressure-clamp technique, used in conjunction with patch-clamp techniques, allows the application of precise pressure/suction waveforms to membrane patches and whole cells. Using step perturbations in pressure, it allows rapid relaxation measurements of the latency, turn-on, turn-off and adaptation kinetics of mechanosensitive membrane ion channels. The pressure-clamp technique also provides the ability to apply gentle and reproducible sealing protocols to establish tight seals and thereby minimize membrane-cytoskeleton disruption which can otherwise alter channel properties.

Animals↗