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At least 793 records · Page 44Linked to original sources

PubMed2002

K(+) transport in the mesonephric collecting duct system of the toad Bufo bufo: microelectrode recordings from isolated and perfused tubules.

We studied the mechanisms of K(+) transport in cells from isolated and perfused collecting tubules and ducts from the mesonephric kidney of the toad Bufo bufo. Cells were impaled with microelectrodes across the basal cell membrane. The basolateral membrane potential (V(bl)) depolarized upon change of bath [K(+)] from 3 to 20 mmol l(-1) demonstrating a large K(+) conductance in this membrane. In collecting tubules and collecting ducts a V(bl) of -66+/-2 mV and -74+/-4 mV depolarized by 30+/-2 mV and 36+/-3 mV, respectively (N=23; 15). The K(+) channel inhibitor Ba(2+) (1 mmol l(-1)) inhibited the basolateral K(+) conductance and depolarized a V(bl) of -64+/-4 mV by 30+/-6 mV (N=8). Luminal K(+) steps (3 to 20 mmol l(-1)) demonstrated a K(+) conductance in the apical cell membrane. In collecting tubules and collecting ducts a V(bl) of -70+/-3 mV and -73+/-3 mV depolarized by 11+/-3 mV and 16+/-3 mV, respectively (N=11; 11). This conductance could also be inhibited by Ba(2+), which depolarized a V(bl) of -71+/-5 mV by 9+/-3 mV (N=5). The pump inhibitor ouabain (1 mmol l(-1)) depolarized V(bl), but addition of furosemide to bath solution did not affect V(bl). The [K(+)] in urine varied from 1.3 to 22.8 mmol l(-1). In conclusion, we propose that the collecting duct system of B. bufo secretes K(+) into the urine via luminal K(+) channels.

Animals↗

PubMed1985

Simultaneous monitoring of electrochemical and unitary neuronal activities by a single carbon fiber microelectrode.

Simultaneous measurements of electrochemical and electrophysiological changes in the substantia nigra pars compacta of the rat were tried with a single carbon fiber microelectrode. Electrochemical detection of catecholamines was done by differential pulse voltammetry. The effects of haloperidol on the level of catecholamines in extracellular spaces and on dopaminergic neuronal discharges were investigated. Haloperidol induced an increase in unitary discharges parallel to the elevation of the catecholamine level. With this technique, direct information can be obtained on the relationship between released catecholamines and unitary neuronal activity.

Animals↗

PubMed1990

Intracellular recording of rat neuron activity at the medial preoptic area of the hypothalamus using triangular wave microelectrode oscillation.

A triangular wave microelectrode oscillating apparatus was constructed to evaluate an intracellular recording of rat neuron activity in the medial preoptic area (POA) of the hypothalamus. In this apparatus, electrodes passed a current with a frequency of 1.0 to 1.8 kHz and a voltage of 2.2 to 3.2 V and produced micro-oscillation of the electrode tip. The electrode was inserted into a neuron of the rat POA in vivo. In vivo recording of the activity of the rat POA neuron was possible. By means of electrical stimulation of the median eminence arcuate of the hypothalamus, an intracellular recording of antidromic, orthodromic or non-responding neuron was also possible. As a result, various components of the action potential such as the resting, threshold and spike potentials, and depolarization and repolarization such as after-hyperpolarization and after-depolarization were observed. The resting potentials ranged from 45 to 90 mV, and POA neurons possessed action potentials of almost the same magnitude. Several problems, however, remain to be solved. In general, the time available for the intracellular recordings is too short. The cells survive only for 15 minutes at the longest and may die in only a few minutes. An improvement of the apparatus was mandatory.

Action Potentials↗

PubMed2006

Fabrication of microelectrodes using the lift-off technique.

The lift-off technique is one of the most prevalent methods for fabricating microelectrodes on a flat surface (e.g., a silicon [Si] wafer). It represents an alternative for metal-etching techniques that often utilize hazardous chemicals in order to define a pattern. This chapter presents an example of patterning gold electrodes on an Si wafer.

Gold↗

PubMed1986

Intracellular free Ca2+ in the course of the Ca2+ paradox and during poisoning. Ca2+-selective microelectrode measurements in the perfused rat heart.

The free intracellular Ca2+ concentration of perfused rat hearts was measured using Ca2+-selective microelectrodes. In Krebs-Ringer bicarbonate buffer + 0.1 mmol/l Ca2+ (controls) the intracellular Ca2+ concentration was 0.87 +/- 0.07 mumol/l and the membrane potential was -51.5 +/- 0.3 mV. Without glucose the membrane potential approached zero after ca. 60 min, whereas the Ca2+ concentration during 110 min increased only slowly to 10.0 mumol/l. During Ca2+-free perfusion (5 min) both parameters did not change significantly. With reintroduction of 2.0 mmol/l Ca2+ the membrane potential rapidly collapsed and the intracellular Ca2+ concentration was elevated above 0.1 mmol/l within two min. Reperfusion with only 0.1 mmol/l Ca2+ decelerated both changes. Poisoning by carbonyl cyanide-p-trifluoromethoxyphenylhydrazone or antimycin A in Ca2+-free Krebs-Ringer bicarbonate buffer increased the intracellular Ca2+ concentration to 30.0 and 25.0 mumol/l, and the membrane potential was collapsed after 16 and 10 min, respectively. In antimycin A- and Ca2+-containing sucrose medium the intracellular Ca2+ during 16 min increased above 1.0 mmol/l, and the membrane potential began to increase only after 10 min. The results are consistent with the postulate of a hypothetical mechanism of cell injury, in which noxious membrane-cytoskeleton interactions are induced by an elevated intracellular Ca2+ concentration. It is concluded that Ca2+ entry via Na/Ca exchange is not fundamentally involved with induction of injury.

Animals↗

PubMed2003

A glass capillary microelectrode based on capillarity and its application to the detection of L-glutamate release from mouse brain slices.

A new glass capillary microelectrode for L-glutamate is described using pulled glass capillaries (tip size, approximately 12.5 microm) with a very small volume (approximately 2 microl) of inner solution containing glutamate oxidase (GluOx) and ascorbate oxidase. The operation of the electrode is based on capillary action that samples L-glutamate into the inner solution. The enzyme reaction by GluOx generates hydrogen peroxide that is detected at an Os-gel-HRP polymer modified Pt electrode in a three-electrode configuration. The amperometric response behavior of the electrode was characterized in terms of the capillarity, response time, sensitivity and selectivity for measurements of L-glutamate. The currents at 0 V vs. Ag/AgCl increased linearly with the L-glutamate concentration from 10 to 150 microM for in vitro and in situ calibrations. The response was highly selective to L-glutamate over ascorbate, dopamine, serotonin and other amino acids. The detection of L-glutamate in the extracellular fluids of different regions of mouse hippocampal slices under stimulation of KCl was demonstrated.

Animals↗

PubMed2004

Attachment of DNA to the carbon fiber microelectrode via gold nanoparticles for simultaneous determination of dopamine and serotonin.

A novel biochemical sensor was fabricated on a carbon fiber microelectrode, which consisted of an inner layer of electrodeposited gold nanoparticles, as a nano-array electrode, and an outer layer of electrodeposited calf thymus ds-DNA at +1.5 V vs. SCE. This modified electrode was characterized by X-ray photoelectron spectroscopy, scanning electron microscope, atomic force microscopy, cyclic voltammetry and differential pulse voltammetry (DPV). It was found that this electrochemical sensor exhibits a strong catalytic activity toward the oxidation of dopamine (DA), serotonin (5-HT) and ascorbic acid (AA), as a result of resolving the anodic voltammetric peaks of DA, 5-HT and AA into three well-defined peaks. Simutaneous DPV determination of DA and 5-HT can be achieved in the presence of 2000-fold AA. The modified electrode shows good sensitivity, selectivity and stability.

Ascorbic Acid↗

PubMed1976

Microelectrode study of spreading depression (SD) in frog retina--general observations of field potential associated with SD.

Using microelectrodes, the field potential change associated with SD (SDP) was recorded from frog retinas conditioned with Cl-free Ringer's. In such retinas, SDP was induced by light or chemical agents such as glutamate, aspartate and K+. The chemicals, when applied iontophoretically, produced a local graded response which eventually triggered SDP. A potential similar to the local response to chemicals was often discerned on the rising phase of SDPs produced by light or occurring spontaneously. The SDP was maximal across an innermost retinal layer 50 mum or less in thickness with the intraretinal polarity predominantly negative, indicating that the major sink of SDP is in the inner plexiform layer. The influence of SDP on the receptor potential was relatively small, but the other components completely disappeared at the beginning of SDP, recovering gradually thereafter. Concomitantly, a strong depolarization occurred in the ganglion cells. Stimulation of the optic nerve could induce SDP, but nerve impulse activity is not important for SDP because tetrodotoxin was unable to prevent SDP due to light or chemical agents.

Adaptation, Physiological↗

PubMed1976

Microelectrode study of spreading depression (SD) in frog retina-Müller cell activity and [K+] during SD--.

By means of K+ microelectrodes, K+ potentials and [K+] were studied in frog retinas conditioned for SD by CL--free Ringer's. A marked increase in [K+]o was observed during SD, the increase being maximal in the inner plexiform layer (up to 50 mM or more) and subsiding towards the distal retina. The extracellular K+ potential change during SD and also the graded K+ potential changes produced locally by iontophoretic injection of SD-stimulant chemicals resembled the membrane potential changes in Müller cells under the same conditions, suggesting that the Müller cells act as K+ electrodes. In retinas conditioned by Cl--free Ringer's Müller cells were swollen. This allowed intracellular recording with K+ electrodes in Müller cells to reveal that upon SD the Müller cells immediately start to cleanse the extracellular space of excess K+ which is probably a product of pathologically enhanced synaptic activity in the inner plexiform layer. The mechanism of SDP, the field potential change associated with SD, is discussed from a proposed model.

Action Potentials↗

PubMed1982

Intracellular measurement of Na activity using neutral carrier Na ion-selective microelectrode.

To measure intracellular Na+ activities, a double-barreled Na ion-selective microelectrode was constructed with a neutral carrier Na+ ligand (ETH 227). The slope constant and detection limit were 56 mV and 3-5 mM, respectively, the selectivity of Na+/K+ being 40-50. In the bullfrog, the cell Na+ was 14.4 mEq/liter for the proximal tubule and 12.6 mEq/liter for the sartorius muscle.

Animals↗

PubMed2003

Implantable microelectrodes with new electro-conductive materials for recording sympathetic neural discharge.

We have developed two new types of bipolar cuff microelectrodes (volume size, 2-3 mm(3)) using electro-conductive rubber or water-absorbent polymer, either of which can be applied to measure sympathetic nerve activity in small animals. A renal nerve bundle of an anesthetized rat was inserted into the center hole of the electrode (diameter, 0.15 mm) through a slit and had good contact with the electrodes. Renal sympathetic nerve activity, which was verified by sympathetic ganglionic blockade, could be recorded using either type of implantable cuff electrode.

Action Potentials↗

PubMed2000

Intracellular microelectrode recording to characterize inhibitory neuromuscular transmission in jejunum of horses.

OBJECTIVE: To evaluate electrical activity of jejunal circular muscle in horses and characterize electrical responses to stimulation by intrinsic inhibitory neurons. SAMPLE POPULATION: Portions of jejunum obtained from horses euthanatized for reasons other than gastrointestinal tract disease. PROCEDURE: Isolated circular muscle preparations were perfused with oxygenated modified Krebs solution. Glass microelectrodes were used for intracellular recording of membrane potentials from single smooth muscle cells. Electrical activity and responses to electrical field stimulation (EFS) of intrinsic neurons in the presence of guanethidine and atropine were recorded. Mediators of responses to nerve stimulation were also evaluated, using N-nitro-L-arginine methyl ester (L-NAME) and apamin. RESULTS: Mean resting membrane potential (RMP) was 41.5+/-1.8 mV. Small membrane potential oscillations were observed in muscle cells. Single or multiple action potentials were often superimposed on the peaks of these oscillations. Spontaneous oscillations and action potentials were blocked by nifedipine. Transient hyperpolarizations of smooth muscle cell membrane potentials (inhibitory junction potentials [IJP]) were observed in response to electrical field stimulation. The IJP evoked by stimulus trains consisted of an initial fast component followed by a slow component. The L-NAME did not have a significant effect on RMP and did not significantly affect the fast component of IJP at any stimulus frequency tested. In contrast, L-NAME abolished the slow component of IJP observed after trains of pulses. In the continued presence of L-NAME, apamin had no significant effect on RMP but effectively reduced the fast component of IJP. CONCLUSIONS AND CLINICAL RELEVANCE: Findings suggest that inhibitory neurotransmitters supplying equine jejunum act through different ionic mechanisms. Understanding these mechanisms may suggest new therapeutic targets for treatment of motility disorders.

Animals↗

PubMedDate not supplied

Microelectrode measurements of the transmembrane potential in baby hamster kidney, (Chinese hamster ovary), NG108-15 neuroblastoma and Swiss 3T3 cells at 37.0 or 43.0 degrees C.

Hyperthermia affects the physical state and function of the plasma membrane. This could alter the transmembrane potential (Vm) and associated functions in a manner that promotes cell killing. Previous investigations have reported differing results of the effect of heat on Vm, possibly due to artifacts associated with the methods employed to measure Vm indirectly. One such artifact is a membrane depolarization induced by cationic probes, as demonstrated in this paper. In this study, glass microelectrodes were used to avoid these artifacts and to make direct electrical measurements of Vm. Following 25 min-30 min at 43.0 degrees C, The mean Vm of Chinese hamster ovary (CHO) cells, within clusters of six or more cells, decreased from -16 +/- 5 to -38 +/- 6 mV, and remained at these levels during incubation times up to 3 h. All CHO cells resumed a normal Vm within 4.5 h after returning to 37.0 degrees C, regardless of the time of exposure at 43.0 degrees C (0.5 to 3.0 h, with survival levels of 0.7 and 0.001, respectively). The membrane hyperpolarization decreased with cell to cell contact to where isolated cells exhibited no hyperpolarization. CHO cultures with different cell densities (number of cells per cm2), and thus differing degrees of cell to cell contact, were heated and then subjected to the colony formation assay. The degree of cell to cell contact at the time of heating had no effect on survival. Hence, the heat-induced, cell contact dependent hypolarization of CHO cell membranes was unrelated to clonogenic survival.(ABSTRACT TRUNCATED AT 250 WORDS)

3T3 Cells↗

PubMed1980

Measurement of intracellular pH of bullfrog skeletal muscle and renal tubular cells with double-barreled antimony microelectrodes.

A pencil-type antimony microelectrode of double-barreled design with a tip of less than 1 to 2 microns in outside diameter was constructed and used to measure intracellular pH(pHi) on frog sartorius muscle and renal tubular cells. Simultaneous observations of membrane potential difference (EM) were made. The results obtained were as follows: (1) The in vivo pHi of frog sartorius muscle was 7.12 +/- 0.07 (SD) (n = 144); the simultaneously measured EM was -51.1 +/- 7.9 mV. The in vivo pHi of frog proximal tubule was 7.49 +/- 0.07 (n = 221) and the EM Peri across the peritubular membrane was -50.2 +/- 9.0 mV. (2) In proximal tubule in vivo, there was a negative correlation between pHi and EM (r = -.62, p < .05). On the other hand, in sartorius muscle in vivo, a positive correlation between the two was found (r = .85, p < .001). (3) In in vitro sartorius muscle, the pHi was 7.03 +/- 0.14 (n = 9) and EM was -62.4 +/- 4.4 mV within one hour after isolation. (4) Increasing the external potassium concentration in the preparations to 75 mM caused a progressive depolarization by 43.3 +/- 15.9 (m = 4) mV, while pHi changed in the alkaline direction by 0.22 +/- 0.03 pH unit. (5) These results indicate that the pHi in both tissues does not obey the Donnan rule.

Animals↗

PubMed2004

Microelectrode-guided implantation of deep brain stimulators into the globus pallidus internus for dystonia: techniques, electrode locations, and outcomes.

Object. Deep brain stimulation (DBS) of the globus pallidus internus (GPi) is a promising new procedure for the treatment of dystonia. The authors present their technical approach for placement of electrodes into the GPi in awake patients with dystonia, including the methodology used for electrophysiological mapping of the GPi in the dystonic state, clinical outcomes and complications, and the location of electrodes associated with optimal benefit. Methods. Twenty-three adult and pediatric patients who had various forms of dystonia were included in this study. Baseline neurological status and improvement in motor function resulting from DBS were measured using the Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS). Implantation of the DBS lead was performed using magnetic resonance (MR) imaging-based stereotaxy, single-cell microelectrode recording, and intraoperative test stimulation to determine thresholds for stimulation-induced adverse effects. Electrode locations were measured on computationally reformatted postoperative MR images according to a prospective protocol. Conclusions. Physiologically guided implantation of DBS electrodes in patients with dystonia is technically feasible in the awake state in most cases, with low morbidity rates. Spontaneous discharge rates of GPi neurons in dystonia are similar to those of globus pallidus externus neurons, such that the two nuclei must be distinguished by neuronal discharge patterns rather than by rates. Active electrode locations associated with robust improvement (> 50% decrease in BFMDRS score) were located near the intercommissural plane, at a mean distance of 3.7 mm from the pallidocapsular border. Patients with juvenile-onset primary dystonia and those with the tardive form benefited greatly from this procedure, whereas benefits for most secondary dystonias and the adult-onset craniocervical form of this disorder were more modest.

Adolescent↗

PubMed1996

Methods for microelectrode-guided posteroventral pallidotomy.

Methods for localizing the posteroventral globus pallidus intermus are described. The authors' techniques include the use of microelectrodes to record single-unit activity and to microstimulate in human pallidum and its surrounding structures. This technique allows a precise determination of the locations of characteristic cell types in sequential trajectories through the external and internal segments of the pallidum. The location of the optic tract can be determined from microstimulation-evoked visual sensations and recordings of flash-evoked potentials. In addition, microstimulation-evoked motor and sensory responses allow the internal capsule to be identified. The data collected using this technique are an important adjunct to selecting optimum sites to place electrocoagulation lesions for stereotactic posteroventral pallidotomy for refractory Parkinson's disease.

Catheter Ablation↗

PubMed1998

Microelectrode-guided pallidotomy: technical approach and its application in medically intractable Parkinson's disease.

OBJECT: The authors describe the microelectrode recording and stimulation techniques used for localizing the caudal sensorimotor portion of the globus pallidus internus (GPi) and nearby structures (internal capsule and optic tract) in patients undergoing GPi pallidotomy. METHODS: Localization is achieved by developing a topographic map of the abovementioned structures based on the physiological characteristics of neurons in the basal ganglia and the microexcitable properties of the internal capsule and optic tract. The location of the caudal GPi can be determined by "form fitting" the physiological map on relevant planes of a stereotactic atlas. A sensorimotor map can be developed by assessing neuronal responses to passive manipulation or active movement of the limbs and orofacial structures. The internal capsule and optic tract, respectively, can be identified by the presence of stimulation-evoked movement or the patient's report of flashes or speckles of light that occur coincident with stimulation. The optic tract may also be located by identifying the neural response to flashes of light. The anatomical/physiological map is used to guide lesion placement within the sensorimotor portion of the pallidum while sparing nearby structures, for example, the external globus pallidus, nucleus basalis, optic tract, and internal capsule. The lesion location and size predicted by using physiological recording together with thin-slice high-resolution magnetic resonance imaging reconstructions of the lesion were confirmed in one patient on histological studies. CONCLUSIONS: These data provide important information concerning target identification for ablative or deep brain stimulation procedures in idiopathic Parkinson's disease and other movement disorders.

Antiparkinson Agents↗

PubMed1999

Variability in lesion location after microelectrode-guided pallidotomy for Parkinson's disease: anatomical, physiological, and technical factors that determine lesion distribution.

OBJECT: To understand the factors that determine the distribution of lesions after microelectrode-guided pallidotomy for Parkinson's disease, the authors quantitatively characterized lesion location in a cohort of patients who were prospectively followed to determine the effects of pallidotomy on clinical outcome. METHODS: Thirty-three patients underwent volumetric magnetic resonance (MR) imaging after surgery to allow quantitative lesion localization in relation to conventional intraventricular landmarks and, alternatively, more anatomically relevant landmarks. The validity of the method was verified in a cohort of postpallidotomy patients who underwent concurrent volumetric and stereotactic MR imaging in an external head frame. Lesions were distributed over a considerable distance in the anteroposterior (8.8 mm) and mediolateral (8.7 mm) dimensions in relation to the anterior commissure and wall of the third ventricle, respectively. Less variation was seen in lesion location in the dorsoventral dimension (4.8 mm) in relation to the intercommissural plane. CONCLUSIONS: Lesion distribution was not random: lesion locations in the anteroposterior and mediolateral dimensions were highly correlated, such that lesions were distributed from anteromedial to posterolateral, parallel to the border of the globus pallidus internus with the obliquely oriented internal capsule. The factors that led to variability in lesion location were variation in third ventricle width and the oblique anteromedial-to-posterolateral course of the internal capsule. This demonstration of variability of lesion location in a cohort of patients who experienced excellent clinical benefits and minimal postoperative complications emphasizes the importance of anatomical variations in determining lesion position and the need for physiological corroboration for correct lesion placement.

Adult↗