Direct Current Potential Research Articles

Electrobioleaching of base metal sulfides

Bioleaching of base metal sulfides, such as pyrite, chalcopyrite, and sphalerite, under the influence of applied direct current (DC) potentials is discussed. Contributions toward mineral dissolution from three effects, namely, galvanic, applied potential, and microbiological, are analyzed and compared. Sphalerite could be selectively bioleached in the presence of Thiobacillus ferrooxidans under an applied potential of -500 mV (SCE) from mixed sulfides containing sphalerite, pyrite, and chalcopyrite. Bacterial activity and growth were found to be promoted under electrobioleaching conditions. Probable mechanisms involved in the bioleaching of different sulfides under positive and negative applied potentials are discussed.

Absorption of Horseradish Peroxidase in the Endolymphatic Sac: Ultrastructural Cytochemistry Using a New Electrophoretic Technique

Using a newly developed injection technique, the absorption of horseradish peroxidase (HRP) in the endolymphatic sac (ES) of the guinea pig was examined by light and electron microscopy. HRP (molecular weight: 40,000; molecular diameter: about 5-nm) was directly injected into the lumen of the ES by electrophoresis after the recording of a direct current potential in the ES lumen. Both the macrophages floating in the ES lumen and the epithelial cells in the intermediate portion of the ES absorbed intraluminal HRP. The macrophages internalized the intraluminal HRP at a higher rate than the epithelial cells, suggesting that macrophages play a major role in macromolecular absorption in the ES. It was considered that the macrophages took up intraluminal HRP by phagocytosis, while the epithelial cells of the intermediate portion took it up by pinocytosis. In contrast, the epithelial cells in the proximal portion of the ES absorbed little HRP. No penetration through the junctional complexes between epithelial cells was observed in either the intermediate or the proximal portion at any interval after the injection of HRP. This finding indicates that these junctional complexes are impermeable to intraluminal HRP.

Interaction of Catecholamine and Acetazolamide in the Action on the Endolymphatic Sac Direct Current Potential

Our recent studies have revealed that catecholamines depress the endolymphatic sac DC potential (ESP) by beta-adrenergic action, and that acetazolamide (ACTZ), a potent carbonic anhydrase inhibitor, decreases the ESP. The interaction of ACTZ and isoproterenol (Iso), a nonselective beta agonist, in their action on the ESP was examined in the guinea pig. Intravenous administration of Iso (6.25 micrograms/kg/min) and ACTZ (10 mg/kg) reduced the ESP amplitude by 38.5 +/- 5.9% (n = 8) and 39.8 +/- 3.7% (n = 8), respectively. Co-administration of both agents reduced the ESP amplitude by 62.3 +/- 3.3% (n = 8). The ESP change induced by co-administration was significantly larger than that by the administration of each agent alone. Co-treatment with Iso and ACTZ at doses producing near-maximum reduction of the ESP depressed almost all parts of oxygen-dependent components of the ESP. The results suggest that Iso and ACTZ decrease the ESP via mechanisms different from each other, and that oxygen-dependent components of the ESP are composed of Iso- and ACTZ-sensitive parts.

Evidence that beta 2-receptors mediate action of catecholamines on endolymphatic sac DC potential

Our recent study has revealed that catecholamines depress the endolymphatic sac direct current potential (ESP) by the beta-adrenergic action [Mori et al., Am. J. Physiol. 259 (regulatory Integrative Comp. Physiol. 28): R921-R924, 1990]. Beta-Adrenergic receptors have been subclassified into beta 1- and beta 2-receptors. Using beta 1-selective (dobutamine) and beta 2-selective (salbutamol) agonists and a beta 1-selective antagonist (atenolol), we determined the subtype of beta-adrenergic receptors that mediate the action of catecholamines on the ESP. Salbutamol depressed the ESP to a larger degree than dobutamine [34.0 +/- 2.6 (n = 7) vs. 13.0 +/- 2.0% (n = 8)] with a much lower dose (100 vs. 1,000 micrograms/kg). Atenolol failed to block the action of salbutamol on the ESP at a dose of 1 mg/kg, whereas propranolol inhibited it at the same dose. The results indicate that beta 2-receptors mediate the action of catecholamines on the ESP.

Study of Regional Cerebral Blood Flow in Experimental Head Injury: Changes Following Cerebral Contusion and During Spreading Depression

Changes in regional cerebral blood flow (rCBF) following fluid-percussion brain injury (cerebral contusion) were studied in rats using the autoradiographic method. The direct current potential was monitored to identify spreading depression (SD). The rCBF was measured during SD and 2, 4, and 24 hours after injury. rCBF was almost nil in the contused area and decreased considerably in the cortices of the injured side for 4 hours after insult, then recovered by 24 hours. Focal relative rCBF increase occurred in the parietal cortex during SD, and was probably hyperperfusion due to SD. However, the rCBF did not increase over the sham-operated control. The injury probably caused hypoperfusion within 4 hours of insult and abolished the vascular response to SD.

Catecholamines depress endolymphatic sac direct current potential in guinea pigs

To test the possibility that catecholamines have an influence on the function of the endolymphatic sac (ES), which is known to absorb the endolymph, the effect of catecholamines on the ES direct current potential (ESP) was examined in the guinea pig. The ESP was recorded extradurally by the posterior occipital approach. Isoproterenol (Iso), epinephrine (Epi), and norepinephrine (NE) were administered intravenously for 4 min using an infusion pump. Catecholamines reversibly depressed the ESP with the rank order of potency Iso greater than Epi greater than NE. The threshold doses were 0.021, 0.27, and 1.94 micrograms/kg for Iso, Epi, and NE, respectively. beta-Antagonist (propranolol) blocked the action of catecholamines on the ESP but alpha-antagonist (phentolamine) did not. This indicates that beta-adrenergic action induces the ESP change. This study implies that catecholamines may regulate the function of the ES.

A rapid redistribution of hydrogen ions is associated with depolarization and repolarization subsequent to cerebral ischemia reperfusion

1. The aim of this study was to examine the rapid changes in extracellular hydrogen ion activity [( H+]o or pHo) which are associated with depolarization and repolarization subsequent to cerebral ischemia reperfusion. Two parallel studies were performed with different rat models of ischemia: repetitive severe ischemia produced in anesthetized animals by occlusion of the vertebral and carotid arteries and temporary interruption of blood flow in isolated brain. [H+]o and direct current potential (DC potential) were recorded simultaneously in all experiments. Examination of these two parameters was supplemented by recording tissue concentration of carbon dioxide (PtCO2) in the four-vessel occlusion model and assaying major metabolites involved in energy production in experiments with isolated brains. 2. Measurements of [H+]o during ischemia consistently revealed a steady increase of [H+]o on which was superimposed an abrupt and transient fall in [H+]o closely related to the occurrence of the fast negative shift of DC potential characterizing brain-cell depolarization. Analysis of the relationship between the magnitude of the transient fall in H+ and the level of [H+]o at which this occurred showed that the amplitude of the transient fall in H+ increased with tissue acidosis. 3. We propose that this phenomenon is indirect evidence that rapid transfer of acid equivalents occurs across the plasmalemma, concomitantly to its depolarization. Both events probably result from a common cause, i.e., nonspecific increase of the cell-membrane permeability to ions subsequent to opening of membrane channels. 4. Early on during recirculation, an acidotic [H+]o shift associated with membrane repolarization was clearly visible whenever the ionic gradients recovered rapidly.(ABSTRACT TRUNCATED AT 250 WORDS)

Cortical activity, ionic homeostasis, and acidosis during rat brain repetitive ischemia.

Recent data strongly suggest that repetitive ischemic episodes have an adverse cumulative effect on development of edema and tissue damage. We wanted to assess further whether special risks such as exacerbation of extracellular acidification reflecting progressive exhaustion of the capacity to buffer H+ in the extracellular space are associated with repeated short ischemic insults. We monitored spontaneous electrical activity, extracellular direct-current potential, extracellular H+ activity, and tissue PCO2 in the cerebral cortex of rats subjected to four cycles of 3-minute ischemia produced by four-vessel occlusion with 27-minute reperfusion after each insult. Except for electrical activity, which failed to recover fully from the first ischemic insult, all parameters returned to a level close to normal after each reperfusion. Changes during ischemia did not evolve with repetition of the insult. Electrical silence occurred within approximately 20 seconds after the onset of each ischemic episode and always preceded the steep drop of direct-current potential, indicating ischemic depolarization. Each four-vessel occlusion immediately initiated a steep rise of tissue PCO2 and extracellular H+ activity, with extracellular H+ activity reaching a maximum within approximately 145 seconds. Changes in extracellular H+ activity during each recirculation period consistently included an additional and short-lasting increase associated with repolarization, a rapid decrease closely related to that of tissue PCO2, and a slow progressive return to normal. These results suggest that short, repetitive ischemic episodes severe enough to produce cell membrane depolarization and maximum acidosis of the neuronal microenvironment do not have a deleterious cumulative effect on the studied parameters, in particular, on interstitial acidosis.

Metabolic and Hemodynamic Activation of Postischemic Rat Brain by Cortical Spreading Depression

Following transient ischemia of the brain, the coupling between somatosensory activation and the hemodynamic-metabolic response is abolished for a certain period despite the partial recovery of somatosensory evoked responses. To determine whether this disturbance is due to alterations of the stimulus-induced neuronal excitation or to a breakdown of the coupling mechanisms, cortical spreading depression was used as a metabolic stimulus in rats before and after ischemia. Adult rats were subjected to 30 min of global forebrain ischemia and 3-6 h of recirculation. EEG, cortical direct current (DC) potential, and laser-Doppler flow were continuously recorded. Local CBF (LCBF), local CMRglc (LCMRglc), regional tissue contents of ATP, glucose, and lactate, and regional pH were determined by quantitative autoradiography, substrate-induced bioluminescence, and fluorometry. Amplitude and frequency of the DC shifts did not differ between groups. In control animals, spreading depression induced a 77% rise in cortical glucose consumption, a 66% rise in lactate content, and a drop in tissue pH of 0.3 unit. ATP and glucose contents were not depleted. During the passage of DC shifts, transient increases (less than 2 min) in laser-Doppler flow were observed, followed by a post-spreading depression hypoperfusion. A comparable although less expressed pattern of hemodynamic and metabolic changes was observed in the postischemic rats. Although baseline LCMRglc was depressed after ischemia, it was activated 47% during spreading depression. Lactate increased by 26%, pH decreased by 0.3 unit, and ATP and glucose remained unchanged. The extent of the transient increase in laser-Doppler flow did not differ from that of the control group, and a post-spreading depression hypoperfusion was also found.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypoxia and ion activities within the brain stem of newborn rabbits

Eleven rabbits between the 1st and 28th days of life were anesthetized (ketamine 40 mg/kg and acepromazine 3 mg/kg im) thoracotomized, paralyzed, and artificially ventilated with 50% O2 and 10% O2 in N2 or 100% N2. Three-barreled ion-sensitive microelectrodes were used to measure direct-current potentials, potassium (aK+o) and calcium (aCa2+o) activities, and tissue PO2. During control, mean levels of aK+o and aCa2+o were 4.4 +/- 1.1 and 1.3 +/- 0.3 mM, respectively. During hypoxia, changes in aCa2+o were inconsistent, and aK+o revealed three phases: slow (phase I) and fast (phase II) rate of rise and a saturation level (phase III) at the group mean of 6.8 +/- 2.3 mM. Durations of phases I and II decreased, and their slopes increased with maturation. Hypoxia-related excitation of phrenic nerve activity (PHR) occurred during phase I, and gasplike PHR and/or apnea occurred during phases II and III. During recovery after hypoxia, PHR was independent of aK+o levels. Vagal nerve stimulation caused a rapid increase in aK+o followed by a continuous decay even though stimulation continued. Hypoxia had no significant effect on maximal aK+o increase. We concluded that ion homeostasis is less sensitive to the reduced availability of O2 shortly after birth than it is later in life. This age dependence may have an important role in the high resistance to lack of O2 during the early postnatal period in mammals.

Eicosanoids in Rat Brain during Ischemia and Reperfusion—Correlation to DC Depolarization

The effects of complete ischemia on cerebral arachidonic acid (AA) metabolism were investigated in the isolated perfused rat brain. During 12.5 min of ischemia, AA, 5-hydroxy-6,8,11,14-eicosatetraenoic acid, and 15-hydroxy-5,8,11,13-eicosatetraenoic acid increased 129-, 4-, and 10-fold, respectively, while subsequent reperfusion for 30 min resulted in normalized levels independently of the duration of preceding ischemia. Prostaglandin (PG) F2 alpha, PGE2, PGD2, 6-keto-PGF1 alpha, and thromboxane (Tx) B2 remained at preischemic levels during 12.5 min of complete ischemia. However, at the end of subsequent reperfusion for 30 min, the levels of the prostanoids PGF2 alpha, PGE2, PGD2, 6-keto-PGF1 alpha, and TxB2 increased according to the preceding ischemic time. The levels reached a maximum after 7.5 min of ischemia and were elevated by 7-, 14-, 48-, 3-, and 30-fold, respectively. A prolongation of ischemia of up to 12.5 min was not associated with further increases of prostanoids at the end of reperfusion. The mechanisms underlying the metabolism of eicosanoids are discussed in relation to the changes of cortical direct current potential.

Cortical Spreading Depression is Associated with Arachidonic Acid Accumulation and Preservation of Energy Charge

The present study aimed to study the relation between the release of arachidonic acid (AA) and the energy state in cerebral cortices of rats during single episodes of cortical spreading depression (CSD). The changes in concentrations of AA, labile phosphate compounds [ATP, ADP, AMP, and phosphocreatine (PCr)], and glycolytic metabolites (lactate, pyruvate, glucose, and glycogen) were studied during and following the large change of the local direct current (DC) potential. Free AA increased markedly during the DC shift, continued to increase during the subsequent 3 min, and returned to control levels at 4-5 min after CSD. PCr decreased by 38% in the first minutes following the DC shift, while ADP increased by 38%. Both returned to normal within a few minutes. ATP, AMP, and energy charge remained constant throughout the experimental period. Glucose decreased by 47% and glycogen by 34% for a few minutes following CSD, while lactate increased by 105% at 2-3 min and by 77% at 4-5 min after CSD. The metabolites returned to control levels at 10 min after CSD. Considering the constant energy charge at all time points during CSD, it is suggested that the AA rise reflects augmented phospholipase activity due to either increased intracellular [Ca2+] or receptor stimulation or both. The possibility that N-methyl-D-aspartate receptors play a role in the release of AA, and that free AA in turn could be part of the mechanism of CSD, is discussed.

Electrostatic Precipitation of Aerosols Under Zero Net Flow Condition

The efficiency of aerosol removal by electrostatic precipitation has been studied in an enclosure formed between the electrodes of a cylindrical condenser. The key feature of this arrangement is that, unlike most other electrostatic precipitator systems, the aerosol source is fully contained within the enclosure and there is no net air throughput. In the experiments, the central electrode was charged to direct current potentials of up to 30 kV and supported small carbon fiber brushes, the resultant corona discharge from which produced copious gaseous ions. Measurements were made of the relationship between the ion current and applied electrode voltage and of the decay of preestablished aerosol clouds derived from the abrasion of flax twine. These latter measurements were carried out using a size-selective optical particle counter which gave simultaneous results for particles in two different size ranges. Theoretical models based on appropriate assumptions regarding the effect of the ion space charge distr...

Slow potentials of the cerebral cortex and behavior.

This review concentrates on scalp-recorded direct current potentials that appear as event-related potentials (ERPs)

Spreading Depression Following Experimental Head Injury in the Rat

The direct current (DC) potential and electroencephalographic (EEG) changes were continuously monitored following fluid percussion head injury (brain contusion) in 10 conscious rats. Local cerebral glucose utilization (LCGU) was measured by the autoradiographic [14C]deoxyglucose method. Measurement of LCGU was started at the lowest point of the first or second DC potential negative shift when it occurred, and 2 hours after contusion if no DC potential changes were observed. The DC potential did not change in four rats (Group A), whereas DC potential negative shifts together with marked suppression of EEG activity occurred at 54 +/- 6.9 minutes after injury in six rats (Group B). In Group A, LCGU was decreased nonsignificantly in both the right and left cortices. In Group B, however, LCGU in the lesioned cortex rose to 160-190% of the level observed in the contralateral cortex (p less than 0.05). The autoradiographic pattern in Group B was identical to that seen in spreading depression. These findings can contribute to the effort to better understand the pathophysiology of head injury.

A new model for inducing transient cerebral ischemia and subsequent reperfusion in rabbits without craniectomy.

An artificial ball removable by an attached fiber was injected into the middle cerebral artery (MCA) of 16 rabbits, allowing the study of transient (5, 10, 15, or 30 minutes) cerebral ischemia without craniectomy. Measurements of available oxygen (aO2) in the ischemic core (the ventral part of the temporal area) followed by histologic examination verified the embolization. Electroencephalographic power spectra and steady (direct current) potentials were recorded bilaterally on the convexity remote from the actual lesion but still supplied by the MCA. Local cerebral blood flow and aO2 in the border zone between the anterior cerebral artery and the occluded MCA were measured. Embolization caused typical ischemic changes ipsilaterally and alterations characteristic of diaschisis contralaterally. Extreme border zone hyperemia developed without significant aO2 changes in the same region. Restoration of circulation via the circle of Willis induced gradual normalization. Our model for controlled embolization and recirculation proved suitable for detailed studies of the complex changes in brain function caused by transient ischemia.

A new fabrication technique for directly coupled transmural cardiac electrodes.

Many current attempts at electrophysiological elucidation of cardiac arrhythmia mechanisms have centered around activation sequence mapping. This is most commonly performed with polarized unipolar or bipolar metal electrodes, which, because of unstable direct current (DC) base-line potentials, necessitate alternating current (AC)-coupled amplification. An ideal nonpolarizable unipolar electrode offers unhindered exchange of charge allowing for stable DC recordings of biological electrical activity. In addition to activation information, DC unipolar recordings enable quantitation of systolic and diastolic potentials, other low-frequency phenomena of interest such as repolarization, as well as rapid recovery from such rapid extreme potential shifts such as defibrillation. Previous attempts to apply nonpolarizable electrodes to transmural cardiac investigations required complex wick electrode techniques to prevent mechanical movement of the fluid-metal interface when chlorided silver wire was used. We have developed a technique to fabricate miniature sintered Ag-AgCl electrodes that are mounted at various locations on a 20-gauge stainless steel needle permitting stable transmural DC unipolar electrogram recordings in vivo. The electrodes are low noise, rugged, sterilizable, and reusable and should prove useful in three-dimensional electrophysiological characterization of the heart.

Endolymphatic pressure in experimental hydrops.

Perilymphatic and endolymphatic pressures were consecutively measured by means of a servomechanical nulling pressure system through the round window and basilar membrane one to 2.5 months after obliteration of the left endolymphatic sac and duct in seven guinea pigs. The position of the pipette was monitored by the simultaneous recording of the direct current potential through the micropipette used for the pressure measurement. (1) The perilymphatic and endolymphatic pressures of the control ears were equal. (2) The histological evaluation showed that the ears operated on had a significantly greater endolymphatic space than the control ears. (3) The endolymphatic pressure of the ear operated on was significantly higher (0.78 +/- 0.32 mm Hg) than that of the perilymph. (4) The endolymphatic direct current potential was equal in both ears.

Study of local cerebral glucose utilization in experimental head injury. Natural course and presence of hypermetabolic state after cerebral contusion.

Local cerebral glucose utilization (LCGU) was studied in 23 awake rats following fluid percussion injury (cerebral contusion). In this system, percussion energy was created by a hammer hitting a vinyl chloride membrane with thickness of 0.5 mm and diameter of 100 mm. This system produced a biphasic impact, which would do no unfavorable damage to the brain stem, but cause a reproducible localized cerebral contusion. The LCGU was quantitatively measured by the [14C]deoxyglucose autoradiographic method (Sokoloff). Six rats were controls. LCGU was studied at 1, 2, 4, and 24 hours following injury. [14C]deoxyglucose uptake was remarkably decreased at the center of the contusion and LCGU was mildly decreased at 1 and 4 hours, and definitely at 24 hours over the ipsilateral hemisphere. Interestingly there were two different types of behavior in LCGU changes at 2 hours after injury; no change or slight decrease in 4 of 6 rats (Group A) and remarkable increase (more than 150%) all over the cortex and the hippocampus of the ipsilateral side in 2 of 6 rats (Group B). This unique phenomenon in Group B—“hypermetabolic state”—resembles the autoradiographic findings in cortical spreading depression, which reportedly show remarkable increase of extracellular K+ and negative shift of direct current (DC) potential, associated with increased glucose uptake of the brain. Persistent oligemia was also reported following cortical spreading depression. The authors observed negative shift of DC potential between 1 and 4 hours, most frequently around 2 hours, after fluid percussion injury (unpublished data). If this hypermetabolic state following experimental head injury is associated with persistent oligemia, as reported in cortical spreading depression, cerebral metabolism would be trapped in a vicious cycle. Secondary brain damage is quite possible due to the above reason, and 2 hours after injury would be the critical period for any trial of treatment.

Infarct rim: effect of hyperglycemia on direct current potential and [14C]2-deoxyglucose phosphorylation.

Focal ischemia was produced by occlusion of the right middle cerebral artery (MCA) in normo- and hyperglycemic rats. In the cortical infarct rim, regional [14C]2-deoxyglucose [( 14C]2-DG) phosphorylation was correlated to spontaneous transient changes in extracellular potassium recorded as direct current (DC) potential deflections. In normoglycemic rats the DC potential showed transient but recurrent deflections in the first hours following MCA occlusion. The 2-DG phosphorylation was elevated by 200% in the same area. In contrast, hyperglycemic rats had no, or a single, deflection of the DC potential in the rim, and the 2-DG phosphorylation remained normal. The same pattern was obtained by application of 3 M KCl to the exposed cortex. In normoglycemia potassium application resulted in recurrent deflections of the DC potential, and 2-DG phosphorylation increased in most parts of the hemisphere. Hyperglycemic animals had a nearly stable DC potential, and 2-DG phosphorylation increased only in the tissue area situated directly below the site of potassium application. The results indicate that metabolism in the cortical infarct rim is stimulated by spontaneous and recurrent changes in extracellular potassium--a phenomenon that may be related to spreading depression--and that the metabolism remained normal in the same area in hyperglycemic animals owing to an inhibition of transient increases of extracellular potassium.