Lithium accumulation by snail neurones measured by a new Li+-sensitive microelectrode

Single-cell calcium monitoring of Caco-2 cell co-cultured with intestinal microbiome through carbon fiber based potentiometric microelectrode

The Caco-2 cells were used as intestinal epithelial cell model to illustrate the hyperuricemia (HUA) mechanism under the co-culture of the imbalanced intestinal microbiome in this work. The uric acid (UA) concentration in the HUA process was monitored, and could be up to 425 μmol/L at 8 h co-cultured with the imbalanced intestinal microbiome. Single-cell potentiometry based on ion-selective microelectrode was used to study extracellular calcium change, which is hypothesized to play an important role in the UA excretion. The potential signal of the calcium in the extremely limited microenvironment around single Caco-2 cell was recorded through the single-cell analysis platform. The potential signal of sharp decrease and slow increase followed within a few seconds indicates the sudden uptake and gradually excretion process of calcium through the cell membrane. Moreover, the value of the potential decrease increases with the increase of the time co-cultured with the imbalanced intestinal microbiome ranging from 0 to 8 h. The Ca2+ concentration around the cell membrane could decrease from 1.3 mM to 0.4 mM according to the potential decrease of 27.0 mV at the co-culture time of 8 h. The apoptosis ratio of the Caco-2 cells also exhibits time dependent with the co-culture of the imbalanced intestinal microbiome, and was 39.1 ± 3.6 % at the co-culture time of 8 h, which is much higher than the Caco-2 cells without any treatment (3.9 ± 2.9 %). These results firstly provide the links between the UA excretion with the apoptosis of the intestinal epithelial cell under the interaction of the imbalanced intestinal microbiome. Moreover, the apoptosis could be triggered by the calcium signaling.

Real-time calcium uptake monitoring of a single renal cancer cell based on an all-solid-state potentiometric microsensor

Introduction: In addition to many cellular processes, Ca2+ is also involved in tumor initiation, progression, angiogenesis, and metastasis. The development of new tools for single-cell Ca2+ measurement could open a new avenue for cancer therapy.

Methods: The all-solid-state calcium ion-selective microelectrode (Ca2+-ISμE) based on carbon fiber modified with PEDOT (PSS) as solid-contact was developed in this work, and the characteristics of the Ca2+-ISμE have also been investigated.

Results: The Ca2+-ISμE exhibits a stable Nernstian response in CaCl2 solutions in the active range of 1.0 × 10−8 - 3.1 × 10−3 M with a low detection limit of 8.9 × 10−9 M. The Ca2+-ISμE can be connected to a patch clamp to fabricate a single-cell analysis platform for in vivo calcium monitoring of a single renal carcinoma cell. The calcium signal decreased significantly (8.6 ± 3.2 mV, n = 3) with severe fluctuations of 5.9 ± 1.8 mV when the concentration of K+ in the tumor microenvironment is up to 20 mM.

Discussion: The results indicate a severe cell response of a single renal carcinoma cell under high K+ stimuli. The detection system could also be used for single-cell analysis of other ions by changing different ion-selective membranes with high temporal resolution.

In vivo monitoring of calcium ions in rat cerebrospinal fluid using an all-solid-state acupuncture needle based potentiometric microelectrode

Acupuncture needles are regarded as ideal materiel for the development of microelectrodes for in vivo sensing. In this work, an all-solid-state ion-selective microelectrode (ISμE) has been developed by coating a calcium ion-selective membrane on an acupuncture needle tip with a diameter of less than 80 μm, which is modified with poly(3,4-ethylenedioxythiophene)-poly(sodium 4-styrenesulfonate) as solid contact. The proposed Ca²⁺-ISμE shows a Nernstian response toward Ca²⁺ in the range from 1.0 × 10^-6 to 3.1 × 10^-3 M with a slope of 30.8 ± 0.9 mV/decade (R² = 0.999), and the detection limit is 1.2 × 10^-7 M. The Ca²⁺-ISμE has been used for in vivo monitoring of the calcium changes in rat cerebrospinal fluid (CSF) under the injury of spinal cord transection. The results demonstrate that the calcium concentration in CSF increases sharply from the normal level of 20.6 ± 1.72 μM (n = 3) to 133.2 ± 7.63 μM (n = 3) with a severe fluctuation after spinal cord damage. Thus, the proposed Ca²⁺-ISμE is available for in vivo monitoring of calcium ions with high temporal resolution and flexibility. The detection system can be extended to measure other ions in CSF by changing different ion-selective membranes.

Recent advances in solid-contact ion-selective electrodes: functional materials, transduction mechanisms, and development trends

This article presents a comprehensive overview of recent progress in the design and applications of solid-contact ion-selective electrodes (SC-ISEs).

Integrated multi-ISE arrays with improved sensitivity, accuracy and precision

Increasing use of ion-selective electrodes (ISEs) in the biological and environmental fields has generated demand for high-sensitivity ISEs. However, improving the sensitivities of ISEs remains a challenge because of the limit of the Nernstian slope (59.2/n mV). Here, we present a universal ion detection method using an electronic integrated multi-electrode system (EIMES) that bypasses the Nernstian slope limit of 59.2/n mV, thereby enabling substantial enhancement of the sensitivity of ISEs. The results reveal that the response slope is greatly increased from 57.2 to 1711.3 mV, 57.3 to 564.7 mV and 57.7 to 576.2 mV by electronic integrated 30 Cl⁻ electrodes, 10 F⁻ electrodes and 10 glass pH electrodes, respectively. Thus, a tiny change in the ion concentration can be monitored, and correspondingly, the accuracy and precision are substantially improved. The EIMES is suited for all types of potentiometric sensors and may pave the way for monitoring of various ions with high accuracy and precision because of its high sensitivity.

Dual effect of lithium on NFAT5 activity in kidney cells

Lithium salts are used widely for treatment of bipolar and other mental disorders. Lithium therapy is accompanied frequently by renal side effects, such as nephrogenic diabetes insipidus or chronic kidney disease (CKD), but the molecular mechanisms underlying these effects are still poorly understood. In the present study we examined the effect of lithium on the activity of the osmosensitive transcriptional activator nuclear factor of activated T cells 5 (NFAT5, also known as TonEBP), which plays a key role in renal cellular osmoprotection and urinary concentrating ability. Interestingly, we found different effects of lithium on NFAT5 activity, depending on medium osmolality and incubation time. When cells were exposed to lithium for a relative short period (24 h), NFAT5 activity was significantly increased, especially under isosmotic conditions, resulting in an enhanced expression of the NFAT5 target gene heat shock protein 70 (HSP70). Further analysis revealed that the increase of NFAT5 activity depended primarily on an enhanced activity of the c-terminal transactivation domain (TAD), while NFAT5 protein abundance was largely unaffected. Enhanced activity of the TAD is probably mediated by lithium-induced inhibitory phosphorylation of glycogen synthase kinase 3β (GSK-3β), which is in accordance with previous studies. When cells were exposed to lithium for a longer period (96 h), cellular NFAT5 activity and subsequently expression of HSP70 significantly decreased under hyperosmotic conditions, due to diminished NFAT5 protein abundance, also resulting from GSK-3β inhibition. Taken together, our results provide evidence that lithium has opposing effects on NFAT5 activity, depending on environmental osmolality and exposure duration. The potential impacts of these observations on the diverse effects of lithium on kidney function are discussed.

Activation of DOR attenuates anoxic K+ derangement via inhibition of Na+ entry in mouse cortex

We have recently found that in the mouse cortex, activation of delta-opioid receptor (DOR) attenuates the disruption of K(+) homeostasis induced by hypoxia or oxygen-glucose deprivation. This novel observation suggests that DOR may protect neurons from hypoxic/ischemic insults via the regulation of K(+) homeostasis because the disruption of K(+) homeostasis plays a critical role in neuronal injury under hypoxic/ischemic stress. The present study was performed to explore the ionic mechanism underlying the DOR-induced neuroprotection. Because anoxia causes Na(+) influx and thus stimulates K(+) leakage, we investigated whether DOR protects the cortex from anoxic K(+) derangement by targeting the Na(+)-based K(+) leakage. By using K(+)-sensitive microelectrodes in mouse cortical slices, we showed that 1) lowering Na(+) concentration and substituting with impermeable N-methyl-D-glucamine caused a concentration-dependent attenuation of anoxic K(+) derangement; 2) lowering Na(+) concentration by substituting with permeable Li(+) tended to potentiate the anoxic K(+) derangement; and 3) the DOR-induced protection against the anoxic K(+) responses was largely abolished by low-Na(+) perfusion irrespective of the substituted cation. We conclude that external Na(+) concentration greatly influences anoxic K(+) derangement and that DOR activation likely attenuates anoxic K(+) derangement induced by the Na(+)-activated mechanisms in the cortex.

Nanoscale potentiometry

Potentiometric sensors share unique characteristics that set them apart from other electrochemical sensors. Potentiometric nanoelectrodes have been reported and successfully used for many decades, and we review these developments. Current research chiefly focuses on nanoscale films at the outer or the inner side of the membrane, with outer layers for increasing biocompatibility, expanding the sensor response, or improving the limit of detection (LOD). Inner layers are mainly used for stabilizing the response and eliminating inner aqueous contacts or undesired nanoscale layers of water. We also discuss the ultimate detectability of ions with such sensors and the power of coupling the ultra-low LODs of ion-selective electrodes with nanoparticle labels to give attractive bioassays that can compete with state-of-the-art electrochemical detection.

Potentiometry at trace levels in confined samples: ion-selective electrodes with subfemtomole detection limits

We explore here for the first time the direct potentiometric detectability of calcium, lead, and silver ions in amounts on the order of 300 attomoles at 100 picomolar concentrations without any preconcentration, analyte recycling, or electrocatalytic signal enhancement. The results presented here place zero-current potentiometry among the most sensitive electrochemical methods available.

Glass Nanopore-Based Ion-Selective Electrodes

Glass nanopore-based all-solid-state ion-selective electrodes (ISEs) have been developed to probe the distribution of ionic species at micro- or submicrometer-length scales, e.g., mapping of ion flux through micrometer-sized pores. The all-solid-state ISE was fabricated by sealing a conically etched platinum wire (d = 25-microm; radius of etched tip <10 nm) into a soda lime glass capillary. A Pt disk was exposed by gentle polishing the glass and the disk etched to form a conical pore of submicrometer dimension (radius < approximately 500 nm; depth < approximately 30 microm). Ag was electroplated on the Pt electrode in the pore and gently chloridated to obtain a AgCl/Ag layer within the pore. The AgCl/Ag layer-coated ISE was used as a highly selective Cl- probe in scanning electrochemical microscope experiments to map the ion flux through a micropore. The same ISE was also used as the base transducer of the neutral carrier-doped solvent polymeric membrane. The optimized polymer membranes used for the glass nanopore-based all-solid-state ISE require a higher ratio of plasticizer/polymer (9/1) compared to those for conventional ISE (2/1). An ISE based on deposition of an IrO2 layer at the base of a glass nanopore electrode exhibited a highly sensitive response (79.7 +/- 2.3 mV/pH) to variations in pH and could be used for approximately 3 weeks.

Modern potentiometry

For most chemists, potentiometry with ion-selective electrodes (ISEs) primarily means pH measurements with a glass electrode. Those interested in clinical analysis might know that ISEs, routinely used for the determination of blood electrolytes, have a market size comparable to that of glass electrodes. It is even less well known that potentiometry went through a silent revolution during the past decade. The lower detection limit and the discrimination of interfering ions (the selectivity coefficients) have been improved in many cases by factors up to 10(6) and 10(10), respectively, thus allowing their application in fields such as environmental trace analysis and potentiometric biosensing. The determination of complex formation constants for lipophilic hosts and ionic guests is also covered in this Minireview.

Lithium ions Up-regulate mRNAs encoding dense-core vesicle proteins in nerve growth factor-differentiated PC12 cells

We recently reported that lithium ions induced an up-regulation of cysteine string protein (CSP) gene expression in nerve growth factor (NGF)-differentiated PC12 cells but not in undifferentiated cells. Concomitantly, expression of two other proteins of regulated secretory pathways, synaptophysin (SY) and SNAP-25, was unaffected by lithium. To assess further the specificity of this effect of lithium, we used cDNA arrays. Our data indicate that lithium ions increase the level of mRNA for proteins such as secretogranin II and vesicular monoamine transporter 1 that are preferentially associated with large densecore secretory vesicles (LDCVs) without affecting mRNAs for proteins predominantly affiliated with small synaptic-like vesicles, including the vesicular acetylcholine transporter and SY. This action of lithium is detected in NGF-differentiated PC12 cells but not in undifferentiated cells. These observations suggest that lithium ions modulate the turnover of LDCVs, and this may play a role in mediating the therapeutic action of lithium in manic-depressive illness.

Lithium ions enhance cysteine string protein gene expression in vivo and in vitro

Lithium is a well established pharmacotherapy for the treatment of recurrent manic-depressive illness. However, the mechanism by which lithium exerts its therapeutic action remains elusive. Here we report that lithium at 1 mM significantly increased the expression of cysteine string proteins (CSPs) in a pheochromocytoma cell line (PC12 cells) differentiated by nerve growth factor. These cells concomitantly exhibited increased expression of CSPs in their cell bodies and boutons. Enhanced CSP expression was also observed in the brain of rats fed a lithium-containing diet, which elevated serum lithium to a therapeutically relevant concentration of approximately 1.0 mM. However, both in vitro and in vivo, the expression of another synaptic vesicle protein, synaptophysin, and the t-SNARE, synaptosomal-associated protein of 25 kDa (SNAP-25), was not significantly altered by lithium. These observations indicate that lithium-induced changes of CSP gene expression may contribute to the therapeutic efficacy of this monovalent cation.

Lithium induced changes in intracellular free magnesium concentration in isolated rat ventricular myocytes

We have examined the effect of exposing isolated rat ventricular myocytes to lithium while measuring cytosolic free magnesium ([Mg2+]i) and calcium ([Ca2+]i) levels with the fluorescent, ion sensitive probes mag-fura-2 and fura-2. There was a significant rise in [Mg2+]i after a 5 min exposure to a solution in which 50% of the sodium had been replaced by Li+, but not when the sodium had been replaced by bis-dimethylammonium (BDA). However, there were significant increases in [Ca2+]i when either Na+ substitute was used. The possibility that Li+, which enters the cells, interferes with the signal from mag-fura-2 was eliminated as Li+ concentrations up to 10 mM had no effect on the dye's fluorescence signal. A possible explanation for these findings is that Li+ displaces Mg2+ from intracellular binding sites. Having considered the binding constants for Mg2+ and Li+ to ATP, we conclude that Li+ can displace Mg2+ from Mg-ATP, thus causing a rise in [Mg2+]i. This work has implications for other studies where Li+ is used as a Na+ substitute.

Activation of the Na+/K+ pump current by intra- and extracellular Li ions in single guinea-pig cardiac cells

Li+ is the only ion that can replace the physiological intra- and extracellular activator cations of the Na+/K+ pump. In order to study this singular property of Li+ in some detail, the activation of the Na+/K+ pump current (Ip) by intra- and extracellular Li+ (Li+; Li[o]+) was measured in isolated guinea-pig ventricular myocytes by means of whole cell recording at 34 degrees C and a holding potential of -20 mV. Ip was identified as current blocked by dihydro-ouabain. Half-maximal Ip activation occurred at 23 mM Li(o)+ (K0.5 value) in cells containing Na+ (50 or 100 mM) and at 73 mM Li(o)+ in myocytes containing Li+ (100 mM). The K0.5 value of Ip activation by Li(o)+ increased with depolarisation, suggesting the transfer of 0.2 of an elementary charge across the electric field of the sacrolemma during Li(o)+-binding. An intracellular Li+ concentration of 36 mM caused half-maximal Ip activation in cells superfused with Na+- and Li+-free media containing 1 mM K+. In Na+-free solutions. the Ip-V curve displayed a positive slope at negative membrane potentials. A negative slope at positive potentials was observed in Li+-containing media. It is concluded that Li+ is less efficacious and potent than the physiological pump activator cations. The shape of the Ip-V curves in Na+-free solutions supports the view that the cardiac Na+/K+ pump contains a channel-like structure and suggests that there are voltage-sensitive steps in the pump cycle, apart from the binding of external cations.

Ion transport and membrane potential in CNS myelinated axons I. Normoxic conditions

Compound resting membrane potential was recorded by the grease gap technique during normoxic conditions (37 degrees C) in rat optic nerve, a representative CNS myelinated tract. Mean potential was -47 +/- 3 (SD) mV and remained stable for 2-3 h. Input impedance of a single optic nerve axon was calculated to be approximately 5 Gomega. Contribution of the Na+ pump to resting axonal potential is estimated at -7 mV. Ouabain (10 microM to 10 mM) evoked a dose-dependent depolarization that was maximal at >/=1 mM, depolarizing the nerves to approximately 35-40% of control after 60 min. Inhibiting energy metabolism (CN- and iodoacetate) during high-dose ouabain (1-10 mM) exposure caused an additional depolarization, suggesting additional ATP-dependent, ouabain-insensitive ion transport systems. Perfusion with zero-Na+ (choline substituted) caused a transient hyperpolarization, that was greater than with tetrodotoxin (TTX; 1 microM) alone, indicating both TTX-sensitive and -insensitive Na+ influx pathways in resting rat optic nerve axons. Resting probability (P)K:PNa is calculated at 20:1. In contrast to choline-substituted solution, Li+-substituted zero-Na+ perfusate caused a rapid depolarization due to Na+ pump inhibition and the ability of Li+ to permeate the Na+ channel. TTX reduced, but did not prevent, ouabain- or zero-Na+/Li+-induced depolarization. We conclude that the primary Na+ influx path in resting rat optic nerve axons is the TTX-sensitive Na+ channel, with evidence for additional TTX-insensitive routes permeable to Na+ and Li+. In addition, maintenance of membrane potential is critically dependent on continuous Na+ pump activity due to the relatively high exchange of Na+ (via the above mentioned routes) and K+ across the membrane of resting optic axons.

The effects of lithium on a neuronal in vitro circadian pacemaker

Previous studies have suggested a causal connection between abnormalities of the circadian system and affective disorders. The effectiveness of lithium or rubidium as a treatment for affective disorders and the ability of lithium or rubidium to influence circadian pacemakers has stimulated research into the mechanism of lithium's action on circadian systems. In this study we used a neuronal in vitro circadian pacemaker preparation, the eye of the mollusc Bulla, to examine the cellular effects of lithium and rubidium. Continuous extracellular LiCl application lengthens the period of the circadian rhythm of the Bulla pacemaker in a concentration-dependent manner. Rubidium was found to be more effective than lithium in period lengthening. Stable phase delays were generated by 2-h pulses of 395 mM LiCl applied extracellularly from zeitgeber time (ZT) 5-7 (mid subjective day). Concomitant continuous application of 16 mM LiCl and light (a depolarizing agent) generated period lengthening substantially greater than the arithmetic sum of the modest period lengthening of each treatment alone. Furthermore, LiCl pulses, applied together with depolarizing extracellular KCl concentrations, yielded an increasing magnitude of phase delays with increasing KCl concentration. These data suggest that LiCl acts intracellularly on the circadian pacemaker cells by entering through a voltage-dependent channel, most likely a sodium channel.

Regional and subcellular localization of Li+ and other cations in the rat brain following long-term lithium administration

Rats were given LiCl in their diet (40 mmol/kg dry weight) for at least 3 months to elucidate the regional and subcellular localization of Li+ in the brain as well as the effect of chronic lithium administration on the distribution of other cations. At steady-state the mean concentrations of Li+ were 0.66 mmol/kg wet weight in the whole brain and 0.52 mM in plasma. The tissue/plasma concentration ratio exceeded unity in all anatomical regions. No region showed excessive accumulation of Li+. Whole brain or regional contents of Na+ or K+ were unaffected by lithium treatment. Subcellular Li+ localization was demonstrated in nuclear, crude mitochondrial, and microsomal fractions of whole brain homogenate. Subfractionation of the crude mitochondrial fraction revealed energy-independent intrasynaptosomal and intramitochondrial Li+ and K+ localization at 0-4 degrees C. Li+ administered in vivo disappeared within 10 min from synaptosomes incubated at 37 degrees C. Li+ added in vitro at 1 mM attained a synaptosomal steady-state concentration within 30 min at 37 degrees C. In control rats, synaptosomal concentrations and synaptosomal/medium concentration gradients of cations paralleled their respective in vivo concentrations and gradients. Lithium treatment caused synaptosomal depletion of K+ and Mg2+ and hence probably partial membrane depolarization. Addition of 1 mM Li+ in vitro also caused synaptosomal Mg2+ depletion. The results indicate that Li+ is "accumulated" in brain sediments and synaptosomes following its long-term treatment. The estimated intracellular and intrasynaptosomal Li+ concentrations are lower than predicted by passive distribution according to the Nernst equation, evidencing active extrusion of Li+.

Lithium reduced synaptic transmission and increased neuronal excitability without altering endogenous serotonin, norepinephrine and dopamine in rat hippocampal slices in vitro

1. Extracellular field potentials were recorded in the CA1 pyramidal cell layer following stimulation of stratum radiatum in rat hippocampal slices during superfusion with different concentrations (1, 2, 5, 10, 20, and 30 mM) of lithium (Li+). Control slices were exposed similarly to choline (Ch+) or sodium (Na+). 2. At high concentrations (greater than or equal to 10 mM), Li+, Ch+ and Na+ reduced the amplitude of the field excitatory postsynaptic potential (EPSP). However, Li+ increased, whereas Ch+ and Na+ reduced the population spike amplitude. Thus, Li+ specifically enhanced the excitability of CA1 pyramidal cells. 3. Electrophysiologically monitored slices, plus an additional group exposed to Li+, Ch+ or Na+ without concomitant field potential recordings, were processed for measurement of endogenous levels of serotonin (5-HT), norepinephrine (NE) and dopamine (DA). The mean endogenous levels of 5-HT and NE were not significantly different in 1-30 mM Li+, Ch+ and Na+. Dopamine contents were unchanged after exposure to Li+ and Na+, but were reduced by Ch+. 4. The non-specific effects of Li+ on synaptic transmission and its specific effects on neuronal excitability appeared independent of changes in endogenous 5-HT, NE and DA levels.

Na(+)-HCO3- symport in the sheep cardiac Purkinje fibre

1. Intracellular pH (pHi) was recorded in isolated sheep cardiac Purkinje fibres using liquid sensor ion-selective microelectrodes in conjunction with conventional (3 M-KCl) microelectrodes (to record membrane potential). 2. In HEPES-buffered solution (pH0 7.4), pHi recovery from an intracellular acid load (20 mM-NH4Cl removal) was blocked by 1 mM-amiloride, consistent with the inhibition of Na(+)-H+ exchange. Replacement of the HEPES buffer with CO2-HCO3- caused a transient acidosis followed by an amiloride-resistant recovery of pHi to more alkaline levels (n = 43). This implies the presence of a HCO3(-)-dependent pHi regulatory mechanism. 3. Comparison of the membrane potential with the equilibrium potential for HCO3- ions (EHCO3) estimated during amiloride-resistant pHi recovery, showed that for polarized fibres (membrane potential Em approximately -80 mV), there was a net outward electrochemical driving force for HCO3- ions. Hence the amiloride-resistant pHi recovery cannot be explained in terms of passive HCO3- influx through membrane channels. 4. Removal of external Na+ (Na0+ replaced by N-methyl-D-glucamine) inhibited HCO3(-)-dependent pHi recovery, whereas removal of external Cl- (leading to depletion of internal Cl-; Cl0- replaced by glucuronate) or short-term removal of extracellular K+ had no inhibitory effect. We suggest that a Na(+)-HCO3- co-influx causes the recovery. Replacement of external Na+ with Li+ greatly reduced HCO3(-)-dependent pHi recovery indicating that Li0+ cannot readily substitute for Na0+ on the co-transport. 5. The stilbene drug DIDS (4,4-diisothiocyano-stilbene-disulphonic acid, 500 microM) slowed HCO3(-)-dependent pHi recovery. 6. Depolarization of the membrane potential in high K0+ (44.5 mM) solution or with 5 mM-BaCl2 had no effect upon the rate of HCO3(-)-sensitive pHi recovery. This observation, when coupled with the fact that activation of HCO3(-)-dependent pHi recovery was associated with no consistent change of membrane potential, suggests that the Na(+)-HCO3- co-influx is electroneutral and voltage insensitive. 7. HCO3(-)-dependent pHi recovery was unaffected by the Na(+)-K(+)-2Cl- co-transport inhibitor, bumetanide (150 microM). 8. The contribution of Na(+)-H+ exchange and Na(+)-HCO3- co-transport to net acid efflux was assessed. At a pHi of 6.6, we estimate that the co-transport should account for 20% of total acid equivalent efflux.(ABSTRACT TRUNCATED AT 400 WORDS)

Lithium transport in the mouse brain

Using the stable isotopes of lithium 6Li and 7Li, and the nuclear reaction 6Li(n,alpha)3H for detection, we have studied the isotopic exchange of lithium in various areas of the mouse brain and in the mouse plasma, under conditions of constant concentration of total lithium. The neutron irradiations were performed using 'cold' neutrons, at the European Institute Von Laue-Langevin. The nuclear reaction track densities were determined using an automatic image analyser. In the plasma, the isotopic ratios, 6Li/7Li, were measured using 'Secondary Ion Mass Spectrometry'. The concentration of total lithium in the plasma was kept close to 0.28 mM. The brain concentration of total lithium (referred to the tissue water content) ranged from more than 2 mM in the thalamus to less than 0.65 mM in the white matter of the cerebellum. The Nernst potential of lithium thus ranged from approx. -50 to approx. -20 mV, which means that lithium is probably not far from electrochemical equilibrium between brain cells and plasma. At any moment, the isotopic abundance of 6Li (ratio of 6Li to total lithium) in the different brain areas, were not significantly different from one another. The time-course of the isotopic abundance of 6Li in the brain was fitted by the composition of two exponential terms. The time-course of the isotopic abundance of 6Li in the plasma was also fitted by the composition of two exponential terms. These analytic curves (for the brain and for the plasma) were not significantly different from each other, at the precision of the measurements. This means that the isotopic equilibration of lithium between brain and plasma is almost instantaneous (i.e. accomplished in a few min at the most).

Interaction of lithium with postsynaptic inhibition in guinea pig hippocampal neurons

Intracellular recording techniques were used to study the effects of Li+ on postsynaptic inhibition of CA3 neurons in guinea pig hippocampal slices. Carbachol (0.3 microM) suppressed and phenylephrine (3 microM) enhanced the hyperpolarization induced by baclofen (0.15 microM). Low intracellular concentrations of Li+ (less than 10 microM) suppressed the muscarinic blockade of the K(+)-dependent inhibition, leaving its enhancement by noradrenergic receptor stimulation unchanged. K(+)-dependent inhibition per se was not affected. At high intracellular concentrations Li+ impaired postsynaptic Cl(-)-dependent inhibition by reducing the efficacy of an outward Cl- pump. While the effect of Li+ on the modulation of K(+)-dependent inhibition may be therapeutically relevant, its action on Cl(-)-dependent inhibition may underly some toxic effects.

Intracellular free magnesium in frog skeletal muscle studied with a new type of magnesium-selective microelectrode: interactions between magnesium and sodium in the regulation of [Mg]i

The application of a new type of intracellular magnesium-selective microelectrode based on the neutral carrier ETH5214 to measure intracellular free magnesium ([Mg]i) in frog skeletal muscle fibers is reported. At room temperature (18-20 degrees C) the average values for [Mg]i was 0.93 mmol/l (pMgi = 3.03 +/- 0.42, SD; n = 38 experiments). The regulation of [Mg]i was studied by measuring [Mg]i and [Na]i with ion-selective microelectrodes during alterations of the membrane potential and the transmembrane sodium and magnesium gradients. Depolarization by increasing external [K] from 2.5 mmol/l to 12.5 mmol/l did not significantly influence [Mg]i. Increasing extracellular [Mg] from 1 mmol/l to 10 and 20 mmol/l caused a concentration-dependent rise in [Mg]i and a decrease in [Na]i, whereas removal of external magnesium did not affect [Mg]i. Removal of external [Na] caused an increase in [Mg]i and a decrease of [Na]i. The results show that [Mg]i in frog skeletal muscle is not in thermodynamic equilibrium and suggest that a Na/Mg exchange mechanism may be involved in maintaining low levels of [Mg]i.

Lithium-induced teratogenesis in frog embryos prevented by a polyphosphoinositide cycle intermediate or a diacylglycerol analog

Microinjection of LiCl into prospective ventral blastomeres of the 32-cell Xenopus embryo gives rise to duplication of dorsoanterior structures such as the notochord, neural tube, eyes, and cement gland. We report here that this teratogenic effect of Li+ is prevented by coinjection of equimolar myo-inositol, an intermediate of the polyphosphoinositide cycle. In contrast, epi-inositol, a nonbiological positional isomer of inositol not employed in this cycle, is ineffective at rescuing Li+-injected embryos. Treatment of embryos at stage 7 with the tumor promoter, phorbol myristate acetate (an analog of the polyphosphoinositide cycle-derived second messenger, diacylglycerol), also prevents dorsoanterior duplication of Li+ embryos, while the nontransforming analog, phorbol myristate acetate-4-O-methyl ether, is without effect. Both of these rescuing agents are without obvious effects on development when administered alone (i.e., without Li+). Li+-selective microelectrode measurements demonstrate that intracellular Li+ levels are identical when Li+ is injected with or without myo-inositol. Clonal analysis shows that blastomeres injected with Li+ plus myo-inositol make a normal contribution of progeny to the later embryo. Because Li+ is a well-established inhibitor of the polyphosphoinositide cycle and can thereby have profound effects on cellular myo-inositol and diacylglycerol levels, these observations concerning inositol-mediated rescue suggest a role for altered polyphosphoinositide cycle activity in lithium-induced teratogenesis.

Depolarization of brain cortex slices and synaptosomes by lithium. Determination of K+-equilibrium potential in cortex slices

K+-equilibrium potential was determined in brain cortex slices of rat by measuring 86Rb+ distribution between the extra- and intracellular space. The ratio of internal to external Rb+ concentration was 39 +/- 1.8, corresponding to a resting membrane potential of 93.8 mV. Li+ (1-126 mM) decreased the membrane potential in both cortex slices and synaptosomes in a concentration-dependent manner. The presence of 1 mM Li+ was enough to cause a slight but distinct depolarization. During incubation in Li+-containing medium slices took up K+; however, for depolarization the presence of extracellular Li+ seemed to be necessary.

Lithium distribution in mania: plasma and red blood cell lithium, clinical state, and monoamine metabolites during lithium treatment

We examined red blood cell (RBC) and plasma lithium concentrations and RBC/plasma lithium ratios in 14 manic patients during lithium treatment as part of the National Institute of Mental Health's Collaborative Program on the Psychobiology of Depression, Biological Studies. All of the lithium measures increased during treatment, especially RBC lithium. There were positive correlations between the RBC lithium concentration and the RBC/plasma lithium ratio and their maximal values in a single-dose pharmacokinetic experiment before treatment. After 5 and 16 days of treatment, patients with good subsequent outcome had higher RBC/plasma lithium ratios than did patients with poor outcome. Early in treatment, there was a negative correlation between lithium concentrations and severity of mania. During treatment, there was a negative correlation between RBC lithium and urinary MHPG excretion. There was a positive correlation between RBC or plasma lithium during the first few days of treatment and subsequent reduction in norepinephrine excretion during treatment. At 3 weeks, there were negative correlations between reductions in catecholamine measures and lithium concentrations. These data suggest that there are changes in the sensitivity of behavior and catecholamine function to lithium during treatment. RBC concentrations of lithium appear to be a potentially useful indicator of its behavioral and neurochemical effects.

Lithium slows neuronal calcium regulation in the snail Helix pomatia

Steady-state and transient changes in intracellular calcium concentrations ([Ca2+]i) of snail neurons (Helix pomatia) were measured by the Ca2+ indicator Arsenazo(III) following manipulation of the extracellular concentration of lithium chloride (LiCl). Application of LiCl in concentrations equivalent to those used in the treatment of manic-depressive illness produces slowing in Ca2+ reequilibration after Ca2+-influx during depolarization, concomitantly with steady-state elevation of [Ca2+]i of about 100 nM, suggesting a change in Ca2+ reequilibration as a prominent action of LiCl. This mechanism may be relevant to the therapeutic effects of LiCl.

Lithium transport across squid axon membrane

This paper describes the pathways for lithium transport across the axonal membrane of squid. We were able to show that the membrane of this classical neuronal preparation possesses the lithium transport mechanisms previously identified in red blood cells. It is now possible to predict that the lithium treatment-induced changes in choline and lithium transport that have been observed in red blood cells of manic depressive patients also occur in nerve membrane.

Effects of lithium on electrical activity and potassium ion distribution in the vertebrate central nervous system

Three different regions of the vertebrate central nervous system maintained in vitro (frog spinal cord, guinea pig olfactory cortex and hippocampus) have been used to investigate how Li+ influences membrane potential, membrane resistance, action potentials, synaptic potentials and the transmembrane K+-distribution of neurons and glial cells. In view of the therapeutic action of Li+ in manic-depressive disease, a special effort was made to determine the threshold concentration for the actions of Li+ on the parameters described above. It was observed that Li+ induced a membrane depolarization of both neurons and glial cells, a decrease of action potential amplitudes, a facilitation of monosynaptic excitatory postsynaptic potentials and a depression of polysynaptic reflexes. The membrane resistance of neurons was not altered. Li+ also induced an elevation of the free extracellular potassium concentration and a decrease of the free intracellular potassium concentration. Furthermore, in the presence of Li+ a slowing of the recovery of the membrane potential of neurons and glial cells, and of the extracellular potassium concentration after repetitive synaptic stimulation was observed. The threshold concentrations for the effects of Li+ were below 5 mmol/l in the frog spinal cord and below 2 mmol/l in the guinea pig olfactory cortex and hippocampus. The basic mechanism underlying the action of Li+ may be an interaction with the transport-function of the Na+/K+ pump.

Transport pathways for lithium ions in neuroblastoma x glioma hybrid cells at 'therapeutic' concentrations of Li+

The pathways of Li+ transport in neuroblastoma X glioma hybrid cells were studied at 2 mM external Li+. Five components of Li+ transport were identified. (1) A Na+-dependent Li+ countertransport system mediating Li+ transport in both directions across the plasma membrane. This transport pathway is insensitive to ouabain or external K+. It shows trans-stimulation (i.e. acceleration of Li+ extrusion by external Na+ and stimulation of Li+ uptake by internal Na+) and cis-inhibition (i.e. reduction of Li+ uptake by external Na+). (2) The Na+-K+ pump mediates Li+ uptake but not Li+ release in cells with physiological Na+ and K+ content. Li+ uptake by the pump in choline media is inhibited by both external Na+ and K+. In Na+ media, external K+ exhibits a biphasic effect: in concentrations up to about 1 mM, K+ accelerates, and at higher concentrations, K+ inhibits Li+ uptake by the pump. (3) Li+ can enter the voltage-dependent Na+ channel. Li+ uptake through this pathway is stimulated by veratridine and scorpion toxin, the stimulation being blocked by tetrodotoxin. Residual pathways comprise (4) a saturable component, which is comparable to basal Na+ uptake, and (5) a ouabain-resistant component promoting Li+ extrusion against an electrochemical gradient in choline media. The mechanisms for Li+ extrusion described here possibly explain how neuronal cells maintain the steady-state ratio of internal to external Li+ below 1 during chronic exposure to 1-2 mM external Li+.