Fecal Deployment: An Alternative Way of Defensive Host Plant Cardenolide Use by Lilioceris merdigera Larvae

The brilliant red Lilioceris merdigera (Coleoptera, Chrysomelidae) can spend its entire life cycle on the cardenolide-containing plant Convallaria majalis (lily of the valley) and forms stable populations on this host. Yet, in contrast to many other insects on cardenolide-containing plants L. merdigera does not sequester these plant toxins in the body but rather both adult beetles and larvae eliminate ingested cardenolides with the feces. Tracer feeding experiments showed that this holds true for radioactively labeled ouabain and digoxin, a highly polar and a rather apolar cardenolide. Both compounds or their derivatives are incorporated in the fecal shields of the larvae. The apolar digoxin, but not the polar ouabain, showed a deterrent effect on the generalist predatory ant Myrmica rubra, which occurs in the habitat of L. merdigera. The deterrent effect was detected for digoxin both in choice and feeding time assays. In a predator choice assay, a fecal shield derived from a diet of cardenolide-containing C. majalis offered L. merdigera larvae better protection from M. rubra than one derived from non-cardenolide Allium schoenoprasum (chives) or no fecal shield at all. Thus, we here present data suggesting a new way how insects may gain protection by feeding on cardenolide-containing plants.

Digoxin as an emerging therapy in noncardiac diseases

The cardiac glycoside (CG) digoxin is a generic drug approved for the treatment of heart failure and supraventricular arrhythmias. Over the past few decades, substantial strides have been made toward repurposing digoxin to treat various noncardiac diseases. Here, we evaluate recent insights into basic and clinical work related to noncardiac use of digoxin.

FXYD3 facilitates Na+ and liquid absorption across human airway epithelia by increasing the transport capacity of the Na/K ATPase

Na/K ATPase activity is essential for ion transport across epithelia. FXYD3, a γ subunit of the Na/K ATPase, is expressed in the airway, but its function remains undetermined. Single-cell RNA sequencing and immunohistochemistry revealed that FXYD3 localizes within the basolateral membrane of all airway epithelial cells. To study FXYD3 function, we reduced FXYD3 expression using siRNA. After permeabilizing the apical membrane with nystatin, epithelia pretreated with FXYD3-targeting siRNA had lower ouabain-sensitive short-circuit currents than control epithelia. FXYD3-targeting siRNA also reduced amiloride-sensitive short-circuit currents and liquid absorption across intact epithelia. These data are consistent with FXYD3 facilitating Na+ and liquid absorption. FXYD3 may be needed to maintain the high rates of Na+ and fluid absorption observed for airway and other FXYD3-expressing epithelia.

In Silico Study towards Repositioning of FDA-Approved Drug Candidates for Anticoronaviral Therapy: Molecular Docking, Molecular Dynamics and Binding Free Energy Calculations

The SARS-CoV-2 targets were evaluated for a set of FDA-approved drugs using a combination of drug repositioning and rigorous computational modeling methodologies such as molecular docking and molecular dynamics (MD) simulations followed by binding free energy calculations. Six FDA-approved drugs including, Ouabain, Digitoxin, Digoxin, Proscillaridin, Salinomycin and Niclosamide with promising anti-SARS-CoV-2 activity were screened in silico against four SARS-CoV-2 proteins—papain-like protease (PLpro), RNA-dependent RNA polymerase (RdRp), SARS-CoV-2 main protease (Mpro), and adaptor-associated kinase 1 (AAK1)—in an attempt to define their promising targets. The applied computational techniques suggest that all the tested drugs exhibited excellent binding patterns with higher scores and stable complexes compared to the native protein cocrystallized inhibitors. Ouabain was suggested to act as a dual inhibitor for both PLpro and Mpro enzymes, while Digitoxin bonded perfectly to RdRp. In addition, Salinomycin targeted PLpro. Particularly, Niclosamide was found to target AAK1 with greater affinity compared to the reference drug. Our study provides comprehensive molecular-level insights for identifying or designing novel anti-COVID-19 drugs.

IKs inhibitor JNJ303 prolongs the QT interval and perpetuates arrhythmia when combined with enhanced inotropy in the CAVB dog

INTRODUCTION

Impaired I_Ks induced by drugs or due to a KCNQ1 mutation, diagnosed as long QT syndrome type 1 (LQT1) prolongs the QT interval and predisposes the heart to Torsade de Pointes (TdP) arrhythmias. The anesthetized chronic AV block (CAVB) dog is inducible for TdP after remodeling and I_Kr inhibitor dofetilide. We tested the proarrhythmic effect of I_Ks inhibition in the CAVB dog, and the proarrhythmic role of increased contractility herein.

METHODS

Dofetilide-inducible animals were included to test the proarrhythmic effect of 1) I_Ks inhibition by JNJ303 (0.63 mg/kg/10min i.v.; n = 4), 2) I_Ks inhibition combined with enhanced inotropy (ouabain, 0.045 mg/kg/1min i.v.; n = 6), and 3) the washout period of the anesthetic regime (n = 10).

RESULTS

JNJ303 prolonged the QTc interval (from 477 ± 53 ms to 565 ± 14 ms, P < 0.02) resembling standardized dofetilide-induced QTc prolongation. Single ectopic beats (n = 4) and ventricular tachycardia (VT) (n = 3) were present, increasing the arrhythmia score (AS) from 1.0 ± 0 to 7.1 ± 6.5. JNJ303 combined with ouabain increased contractile parameters (LVdP/dt_max from 1725 ± 273 to 4147 ± 611 mmHg/s, P < 0.01). Moreover, TdP arrhythmias were induced in 4/6 dogs and AS increased from 1.0 ± 0 to 20.2 ± 19.0 after JNJ303 and ouabain (P < 0.05). Finally, TdP arrhythmias were induced in 4/10 dogs during the anesthesia washout period and the AS increased from 1.1 ± 0.3 to 9.2 ± 11.2.

CONCLUSION

Mimicking LQT1 using I_Ks inhibitor JNJ303 prolongs the QTc interval and triggers ectopic beats and non-sustained VT in the CAVB dog. Induction of the more severe arrhythmic events (TdP) demands a combination of I_Ks inhibition with enhanced inotropy or ending the anesthetic regime.

Repurposing Cardiac Glycosides: Drugs for Heart Failure Surmounting Viruses

Drug repositioning is a successful approach in medicinal research. It significantly simplifies the long-term process of clinical drug evaluation, since the drug being tested has already been approved for another condition. One example of drug repositioning involves cardiac glycosides (CGs), which have, for a long time, been used in heart medicine. Moreover, it has been known for decades that CGs also have great potential in cancer treatment and, thus, many clinical trials now evaluate their anticancer potential. Interestingly, heart failure and cancer are not the only conditions for which CGs could be effectively used. In recent years, the antiviral potential of CGs has been extensively studied, and with the ongoing SARS-CoV-2 pandemic, this interest in CGs has increased even more. Therefore, here, we present CGs as potent and promising antiviral compounds, which can interfere with almost any steps of the viral life cycle, except for the viral attachment to a host cell. In this review article, we summarize the reported data on this hot topic and discuss the mechanisms of antiviral action of CGs, with reference to the particular viral life cycle phase they interfere with.

In vitro antitumoral effects of the steroid ouabain on human thyroid papillary carcinoma cell lines

Ouabain is a steroid described as a compound extracted from plants that is capable of binding to Na⁺ , K⁺ -ATPase, inhibiting ion transport and triggering cell signaling pathways. Due to its positive ionotropic effect, ouabain was used for more than 200 years for the treatment of cardiac dysfunctions. Numerous antitumor effects of ouabain have been described so far; however, its role on thyroid cancer is still poorly understood. Therefore, the aim of the present work was to evaluate the effect of ouabain on the biology of human papillary thyroid cancer cells. For this, three human thyroid cell lines were used: NTHY-ori, a non-tumor lineage, BCPAP and TPC-1, both derived from papillary carcinomas. Cells were cultured in the presence or absence of ouabain. Subsequently, we evaluated its effects on the viability, cell death, cell cycle, and migratory ability of these cell lines. We also investigated the impact of ouabain in IL-6/IL-6R and epithelial to mesenchymal transition markers expression. Our results indicate that ouabain (10^-7 M), decreased the number of NTHY-ori, TPC-1 and BCPAP viable cells and induced cell cycle arrest after in vitro culture, but did not appear to promote cell death. In TPC-1 cells ouabain also inhibited cell migration; increased IL-6/IL-6R expression and IL-6 secretion; and diminished vimentin and SNAIL-1 expression. Collectively, our results indicate that ouabain has an antitumoral role on human papillary thyroid carcinomas in vitro. Even though additional studies are necessary, our work contributes to the discussion of the possibility of new clinical trials of ouabain.

Improving in vitro ciguatoxin and brevetoxin detection: selecting neuroblastoma (Neuro-2a) cells with lower sensitivity to ouabain and veratridine (OV-LS)

Marine biotoxins accumulating in seafood products pose a risk to human health. These toxins are often potent in minute amounts and contained within complex matrices; requiring sensitive, reliable, and robust methods for their detection. The mouse neuroblastoma (Neuro-2a) cytotoxicity assay (N2a-assay) is a sensitive, high-throughput, in vitro method effective for detecting sodium channel-specific marine biotoxins. The N2a-assay can be conducted to distinguish between specific effects on voltage-gated sodium (Na_V) channels, caused by toxins that activate (e.g., ciguatoxins (CTXs), brevetoxins (PbTxs)) or block (e.g., tetrodotoxins, saxitoxins) the target Na_V. The sensitivity and specificity of the assay to compounds activating the Na_V are achieved through the addition of the pharmaceuticals ouabain (O) and veratridine (V). However, these compounds can be toxic to Neuro-2a cells and their application at insufficient or excessive concentrations can reduce the effectiveness of this assay for marine toxin detection. Therefore, during growth incubation, Neuro-2a cells were exposed to O and V, and surviving cells exhibiting a lower sensitivity to O and V (OV-LS) were propagated. OV-LS Neuro-2a cells were selected for 60-80% survival when exposed to 0.22/0.022 mM O/V during the cytotoxicity assay. At these conditions, OV-LS N2a cells demonstrated a 3.5-fold higher survival rate 71% ± 7.9 SD (n = 232), and lower sensitivity to O/V, compared to the original Neuro-2a cells 20% ± 9.0 SD (n = 16). Additionally, OV-LS N2a cells were 1.3-2.6-fold more sensitive for detecting CTX3C 1.35 pg/ml, CTX1B 2.06 pg/ml, and PbTx-3 3.04 ng/ml compared to Neuro-2a cells using 0.1/0.01 mM O/V. Detection of CTX3C in a complex fish matrix using OV-LS cells was 0.0048 pg CTX3C/mg fish tissue equivalent. This work shows the potential for a significant improvement in sensitivity for CTX3C, CTX1B, and PbTx-3 using the OV-LS N2a-assay.

Motor function in an animal model with ouabain-induced bipolar disorder and comorbid anxiety behavior

In a clinical setting, anxiety disorder is highly correlated with bipolar I disorder in humans. However, the comorbidity of anxiety behavior and bipolar disorder still remains unclear in an animal model. This study utilized an ouabain-induced animal mode to examine anxiety and mania in an open field test. In the present study, 5 µl of artificial cerebrospinal fluid (aCSF) or ouabain (10^-5, 10^-4, and 10^-3 M) were administered into the left ventricle. The animals' motor functions and anxiety behaviors were measured for 15 min. The results showed that 10^-3 M ouabain significantly increased the animal's total distance traveled, average speed, and maximum speed compared to the control group. The time spent inside (i.e., how much time rats spent in the center of the square) and the inside-outside times of the central square (i.e., how many times rats ran across the center square) of the higher-concentration groups (10^-4 M and 10^-3 M) were significantly decreased. Therefore, a high concentration of ouabain may induce hyperactivity. The 10^-4 M and 10^-3 M ouabain groups exhibited more anxiety behaviors. The study is the first model to examine comorbid anxiety behaviors and bipolar disorder in an animal model. The study provides some insights for comorbid anxiety and bipolar disorder in clinics.

Substitutions in the cardenolide binding site and interaction of subunits affect kinetics besides cardenolide sensitivity of insect Na,K-ATPase

Substitutions within the cardenolide target site of several insects' Na,K-ATPase α-subunits may confer resistance against toxic cardenolides. However, to which extent these substitutions alter the Na,K-ATPase's kinetic properties and how they interact with different β-subunits is not clear. The cardenolide-adapted milkweed bug Oncopeltus fasciatus possesses three paralogs of the α-subunit (A, B, and C) that differ in number and identity of resistance-conferring substitutions. We introduced these substitutions into the α-subunit of Drosophila melanogaster and combined them with the β-subunits Nrv2.2 and Nrv3. The substitutions Q111T-N122H-F786N-T797A (A-copy mimic) and Q111T-N122H-F786N (B-copy mimic) mediated high insensitivity to ouabain, yet they drastically lowered ATPase activity. Remarkably, the identity of the β-subunit was decisive and all α-subunits were less active when combined with Nrv3 than when combined with Nrv2.2. Both the substitutions and the co-expressed β-subunit strongly affected the enyzme's affinity for Na⁺ and K⁺. Na⁺ affinity was considerably higher for all enzymes expressed with nrv3 while expression with nrv2.2 mostly increased K⁺ affinity. Our results provide the first evidence that resistance against cardenolides comes at the cost of significantly altered kinetic properties of the Na,K-ATPase. The β-subunit can strongly modulate these properties but cannot fully compensate for the effect of the substitutions.

Cognitive flexibility impairment and reduced frontal cortex BDNF expression in the ouabain model of mania

Central infusion of the Na+/K+-ATPase inhibitor, ouabain in rats serves as an animal model of mania because it leads to hyperactivity, as well as reproduces ion dysregulation and reduced brain-derived neurotrophic factor (BDNF) levels similar to that observed in bipolar disorder. Bipolar disorder is also associated with cognitive inflexibility and working memory deficits. It is unknown whether ouabain treatment in rats leads to similar cognitive flexibility and working memory deficits. The present study examined the effects of an intracerebral ventricular infusion of ouabain in rats on spontaneous alternation, probabilistic reversal learning and BDNF expression levels in the frontal cortex. Ouabain treatment significantly increased locomotor activity, but did not affect alternation performance in a Y-maze. Ouabain treatment selectively impaired reversal learning in a spatial discrimination task using an 80/20 probabilistic reinforcement procedure. The reversal learning deficit in ouabain-treated rats resulted from an impaired ability to maintain a new choice pattern (increased regressive errors). Ouabain treatment also decreased sensitivity to negative feedback during the initial phase of reversal learning. Expression of BDNF mRNA and protein levels was downregulated in the frontal cortex which also negatively correlated with regressive errors. These findings suggest that the ouabain model of mania may be useful in understanding the neuropathophysiology that contributes to cognitive flexibility deficits and test potential treatments to alleviate cognitive deficits in bipolar disorder.

Isolation of 6-deoxytetrodotoxin from the pufferfish, Takifugu pardalis, and a comparison of the effects of the C-6 and C-11 hydroxy groups of tetrodotoxin on its activity

Identification of new tetrodotoxin (TTX, 1) analogues would be significant in the elucidation of its biosynthetic pathway and a study of its structure-activity relationships. In this study, a new TTX analogue, 6-deoxyTTX (2), was isolated from the ovary of the pufferfish, Takifugu pardalis, and the structure was determined using spectroscopic methods. Compound 2 was also identified in other marine animals, Nassarius snail and blue-ringed octopuses, using LC-MS. Furthermore, we investigated the voltage-gated sodium channel blocking activity of 2 by examination of the inhibitory activities to cytotoxicity induced by ouabain and veratridine in mouse neuroblastoma cells (Neuro-2a). The activities were then compared with those of 1, 11-deoxyTTX (3), and 6,11-dideoxyTTX (4). The EC50 value for 2 was estimated to be 6.5±2.2 nM, approximately 3-fold larger than that of 1 (2.1±0.6 nM) and approximately 20-fold smaller than that of 3. These results suggested that contribution of the C-6 hydroxy group to the activity is less than that of the C-11 hydroxy group.

[Antiarrhythmic effect of TJ0711]

To study the antiarrhythmic effect of the newly developed alpha/beta-blocker TJ0711, a variety of animal models of arrhythmia were induced by CaCl2, ouabain and ischemia/reperfusion. Glass microelectrode technique was used to observe action potentials of right ventricular papillary muscle of guinea pig. The onset time of arrhythmia induced by CaCl2 was significantly prolonged by TJ0711 at 0.75, 1.5 and 3 mg x kg(-1) doses. TJ0711 (1.5 and 3 mg x kg(-1)) can significantly shorten the ventricular tachycardia (VT) and ventricular fibrillation (VF) duration, the incidence of VF and mortality were significantly reduced. On ischemia-reperfusion-induced arrhythmic model, TJ0711 (0.25, 0.5, 1 and 2 mg x kg(-1)) can significantly reduce the ventricular premature contraction (PVC), VT, VF incidence, mortality, arrhythmia score with a dose-dependent manner. At the same time, rats serum lactate dehydrogenase (LDH) and creatine kinase (CK) activities decreased significantly by TJ0711 (1 and 2 mg x kg(-1)). Ouabain could cause arrhythmia in guinea pigs, when TJ0711 (0.375, 0.75, 1.5 and 3 mg x kg(-1)) was given, the doses of ouabain inducing a variety of arrhythmia PVC, VT, VF, cardiac arrest (CA) were significantly increased with a dose-dependent manner. In the TJ0711 0.1-30 micromol x L(-1) concentration range, guinea pig right ventricular papillary muscle action potential RP (rest potential), APA (action potential amplitude) and V(max) (maximum velocity of depolarization) were not significantly affected. APD20, APD50 and APD90 had a shortening trend but no statistical difference with the increase of TJ0711 concentration. TJ0711 has antiarrhythmic effect on the sympathetic nerve excitement and myocardial cell high calcium animal arrhythmia model. Myocardial action potential zero phase conduction velocity and resting membrane potential were not inhibited by TJ0711. APD20, APD50 and APD90 were shortened by TJ0711 at high concentration. Its antiarrhythmic action mechanism may be besides the action of blocking beta1 receptor, may also have a strong selective blocking action on alpha1 receptor and reducing intracellular calcium concentration.

Pharmacological blockade of gap junctions induces repetitive surging of extracellular potassium within the locust CNS

The maintenance of cellular ion homeostasis is crucial for optimal neural function and thus it is of great importance to understand its regulation. Glial cells are extensively coupled by gap junctions forming a network that is suggested to serve as a spatial buffer for potassium (K(+)) ions. We have investigated the role of glial spatial buffering in the regulation of extracellular K(+) concentration ([K(+)]o) within the locust metathoracic ganglion by pharmacologically inhibiting gap junctions. Using K(+)-sensitive microelectrodes, we measured [K(+)]o near the ventilatory neuropile while simultaneously recording the ventilatory rhythm as a model of neural circuit function. We found that blockade of gap junctions with either carbenoxolone (CBX), 18β-glycyrrhetinic acid (18β-GA) or meclofenamic acid (MFA) reliably induced repetitive [K(+)]o surges and caused a progressive impairment in the ability to maintain baseline [K(+)]o levels throughout the treatment period. We also show that a low dose of CBX that did not induce surging activity increased the vulnerability of locust neural tissue to spreading depression (SD) induced by Na(+)/K(+)-ATPase inhibition with ouabain. CBX pre-treatment increased the number of SD events induced by ouabain and hindered the recovery of [K(+)]o back to baseline levels between events. Our results suggest that glial spatial buffering through gap junctions plays an essential role in the regulation of [K(+)]o under normal conditions and also contributes to a component of [K(+)]o clearance following physiologically elevated levels of [K(+)]o.

Recent experiments towards a model for fluid secretion in Rhodnius Upper Malpighian Tubules (UMT)

Three different methods have been used to improve a model for fluid secretion in Upper Malpighian Tubules (UMT) of the blood sucking insect Rhodnius prolixus. (I) In the first, UMT double perfusions in 5th instar Rhodnius were used to measure their fluid secretion rate. They were stimulated to secrete with 5-HT. Double perfusions allowed access separately to the basolateral and the apical cell membranes with pharmacological agents known to block different ion transport functions, namely ATPases, cotransporters and/or countertransporters and ion and water channels: ouabain, bafilomycin A1, furosemide, bumetanide, SITS, acetazolamide, amiloride, DPC, BaCl(2), pCMBS and DTT. The basic assumption is that changes in water movement reflect changes in ion transport mechanisms. (II) Intracellular Na(+) concentrations were measured with a fluorometric method in dissected R. prolixus UMT, under several experimental conditions. (III) ATPase activities were measured in R. prolixus UMT. A tentative model for the function of the UMT cell is presented. We find that (a) at the basolateral cell membrane, fundamental is a Na(+)-K(+)-2Cl(-) cotransporter; of intermediate importance are the Na(+)-K(+)-ATPase and a ouabain-insensitive Na(+)-ATPase, ion channels and Rp-MIP water channels. (b) At the apical cell membrane, most important are a V-H(+)-ATPase; and a K(+) and/or Na(+)-H(+) exchanger.

The Metabolism of Ouabain in the Rat

The urinary and biliary excretion of ouabain by rats has been estimated by paper chromatographic, colorimetric and biological methods of assay. After a dose of 1 μg./g., ouabain was excreted to the extent of approximately 90 per cent in bile and 4 per cent in urine. No metabolites of ouabain retaining the unsaturated lactone ring could be detected at this dose, but after extremely high doses traces of such metabolites were present. The influence of the polarity of the molecule on its excretion is discussed.

Note on the cardiac effects of nystatin

Nystatin, a polyene antifungal antibiotic, induces systolic arrest of the isolated hearts of the frog, rat or rabbit. In the frog, heart failure induced by raising venous pressure was antagonised and the cardiac outflow was increased. Coronary flow in the perfused heart of the rat or rabbit was decreased.

[Role of renal sympathetic nerves in renal sodium transport in ouabain-hypertensive rats]

OBJECTIVE

To investigate the role of renal sympathetic nerves in renal sodium transport in ouabain-hypertensive rats (OHR).

METHODS

Sixteen male SD rats with sham renal denervation (Sham-RDNX) and 16 with renal denervation (RDNX) were randomly into normal control group and ouabain group to receive intraperitoneal injection of normal saline (1 ml/kg) and ouabain (27.8 µg/kg) once a day, respectively. Systolic blood pressure (SBP), heart rate and body weight were recorded weekly. Food consumption of the rats was determined twice a week. After a 4-week treatment, blood and 24 h urine samples were collected to measure the serum and urinary concentration of sodium, trace lithium and creatinine. Endogenous creatinine clearance rate (Ccr), fractional excretions of sodium (FENa), fractional excretions of lithium (FELi) and fractional reabsorption of sodium in the postproximal tubules (FDRNa) were calculated. Plasma renin activity was determined by radioimmunoassay. Norepinephrine was extracted from the renal tissue and assayed for norepinephrine content by HPLC.

RESULTS

The body weight, food intake and heart rate showed no significant difference among the 4 groups (P > 0.05). After 4 weeks, the SBP of control RDNX group (CDNX) was significantly lower than that of the control Sham-DNX group (Csham)(P < 0.05); the SBP of ouabain RDNX group (ODNX) was also significantly lower than that of ouabain Sham-DNX group (Osham) (P < 0.05); RNDX lowered SBP by about 10 mmHg in both ouabain groups and control groups. The SBP was significantly higher in Osham and ODNX groups than in the corresponding control groups (P < 0.01), also significantly higher in ODNX group than in Csham group (P < 0.01). Ccr showed no significant difference among the 4 groups(P > 0.05). FENa, FELi and FDRNa were significantly lower in ouabain groups than in the corresponding control groups (P < 0.05, P < 0.01, P < 0.05), but FENa, FELi and FDRNa of ODNX group were similar with those of Osham group (P > 0.05); FENa , FELi and FDRNa were similar between CDNX and Csham groups (P > 0.05). The plasma renin activity was comparable between the 4 groups (P > 0.05). Renal norepinephrine level was markedly reduced in RDNX group compared with that in Sham-RDNX group in both ouabain and control groups (P < 0.01).

CONCLUSION

The increase of proximal tubule sodium reabsorption in OHR is not dependent on the renal sympathetic nerve.

OuaSelect, a novel ouabain-resistant human marker gene that allows efficient cell selection within 48 h

Efficient selection of gene-modified cells is required for a number of potential gene therapy applications, as well as molecular biology studies. Ideally, a clinical selection regimen would combine high selection speed, efficiency and efficacy, in addition to clinical grade selection techniques and low immunogenicity. To our knowledge, a selection marker satisfying all these features is so far not available. Ouabain is a clinically used cardiac glycoside and selective Na(+)/K(+)-ATPase inhibitor. On the basis of the high sensitivity of human Na(+)/K(+)-ATPase proteins to ouabain, and rapid killing of cells upon exposure, we have screened the ubiquitously expressed Na(+)/K(+)-ATPase alpha1 subunit for mutations that could greatly increase its resistance to ouabain. Two amino-acid substitutions, Q118R and N129D were sufficient to confer a two log greater resistance to ouabain in HeLa, Jurkat, U2OS cells and in primary cells. Furthermore, following transduction of primary lymphocytes with the alpha1(Q118R/N129D) gene, >99% pure populations of gene-modified cells were achieved with a recovery rate of >80% after 48 h of exposure to ouabain. These results identify the human alpha1(Q118R/N129D) (OuaSelect) as a promising selection marker gene for safe, rapid and cost-effective selection in clinical gene therapy and molecular biology research.

Enhanced Survival of Bone???Marrow-Derived Pluripotent Stem Cells in an Animal Model of Auditory Neuropathy

OBJECTIVE

The loss of spiral ganglion neurons (SGNs) is one of the major causes of profound sensorineural hearing loss (SNHL). Stem cell replacement therapy, which is still in its infancy, has the potential to treat or cure those who suffer from an array of illnesses and degenerative neurologic disorders, including sensorineural deafness (SNHL). Little is known about the potentials of mesenchymal stem cells (MSCs) and their ability to take on properties of SGNs. The two main purposes of this study were to evaluate the survival of mouse MSCs transplanted into normal and ouabain-treated gerbil cochleae and to determine the migratory patterns of MSCs with two differing injection methods.

SUBJECTS

Thirty-two Mongolian gerbils, 3 to 4 months old, were used as recipients, and four 6-week-old TgN(ACTbEGFP) mice that ubiquitously express green fluorescent protein (GFP) were used as donors.

DESIGN

The animals were deafened by ouabain, which damaged SGNs while leaving hair cell systems intact. After 4 weeks of recovery, the animals received an intraperilymphatic transplantation of 1.0x10(6) GFP-positive undifferentiated MSCs via two different injection methods: scala tympani injection and modiolar injection. Seven days after the transplantation, the survival of MSCs was evaluated by microscopic examination of frozen sections cut through the cochleae of the recipient animals. The number of profiles was counted on the five most central modiolar sections. One-way analyses of variance (ANOVA) were used to determine any significantdifferences among mean profile counts across the experimental conditions.

RESULTS

Our findings indicated that undifferentiated MSCs were able to survive in the modiolus both in the control and the ouabain-treated cochleae. The average number of profiles found in the modiolus was greater in the ouabain-treated cochleae than in the control cochleae. This difference was statistically significant (P<.01) as determined using a one-way ANOVA and an ad hoc Tukey-Kramer's test. With the scala tympani injection, there were no profiles found in the modiolus either in the control or ouabain-treated cochleae. This finding may indicate that donor MSCs need to be directly injected into the modiolus to replace injured SGNs. Finally, there was no evidence of hyperacute rejection in any of the gerbils despite the use of xenotransplantation.

CONCLUSIONS

These findings may have important clinical implications as a means of delivering MSCs in the cochlea for stem-cell replacement therapy. Survival of transplanted MSCs into the modiolus of the cochlea may result in regeneration of damaged SGNs.

Pharmacological activators of AMP-activated protein kinase have different effects on Na+ transport processes across human lung epithelial cells

BACKGROUND AND PURPOSE

AMP-activated protein kinase (AMPK) is activated by metformin, phenformin, and the AMP mimetic, 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside (AICAR). We have completed an extensive study of the pharmacological effects of these drugs on AMPK activation, adenine nucleotide concentration, transepithelial amiloride-sensitive (I(amiloride)) and ouabain-sensitive basolateral (I(ouabain)) short circuit current in H441 lung epithelial cells.

EXPERIMENTAL APPROACH

H441 cells were grown on permeable filters at air interface. I(amiloride), I(ouabain) and transepithelial resistance were measured in Ussing chambers. AMPK activity was measured as the amount of radiolabelled phosphate transferred to the SAMS peptide. Adenine nucleotide concentration was analysed by reverse phase HPLC and NAD(P)H autofluorescence was measured using confocal microscopy.

KEY RESULTS

Phenformin, AICAR and metformin increased AMPK (alpha1) activity and decreased I(amiloride). The AMPK inhibitor Compound C prevented the action of metformin and AICAR but not phenformin. Phenformin and AICAR decreased I(ouabain) across H441 monolayers and decreased monolayer resistance. The decrease in I(amiloride) was closely related to I(ouabain) with phenformin, but not in AICAR treated monolayers. Metformin and phenformin increased the cellular AMP:ATP ratio but only phenformin and AICAR decreased cellular ATP.

CONCLUSIONS AND IMPLICATIONS

Activation of alpha1-AMPK is associated with inhibition of apical amiloride-sensitive Na(+) channels (ENaC), which has important implications for the clinical use of metformin. Additional pharmacological effects evoked by AICAR and phenformin on I(ouabain), with potential secondary effects on apical Na+ conductance, ENaC activity and monolayer resistance, have important consequences for their use as pharmacological activators of AMPK in cell systems where Na+K+ATPase is an important component.

Abnormalities of Na/K ATPase in migraine with aura

It has been previously shown from our laboratory that abnormal functioning of Na/K ATPase can cause spreading depression, the likely mechanism of migraine aura. We used lymphocytes to investigate whether or not membrane Na/K ATPase is altered in migraine with aura patients. Lymphocytes were prepared from such patients, aged 20-45 years, and from age-matched healthy volunteers (controls). The binding of 3H- ouabain was studied using increasing concentrations (0.5-25 nm) of this radioligand, specific for Na/K-ATPase. We studied 19 migraine with aura patients and 22 healthy volunteers, matched for age and sex. B(max) (fmol/mg protein) and K(D) (nM) were not different between patients and controls. However, their ratio (B(max)/K(D)) was higher in patients than in controls. B(max) was (mean +/- SD) 270 +/- 110 fmol/mg protein in controls, and 360 +/- 230 in migraine with aura patients (P = 0.10, t-test). K(D) was (mean +/- SD) 2.8 +/- 1.5 nm in controls, and 2.9 +/- 3.2 nm in migraine with aura patients (P = 0.88, t-test). B(max)/K(D) was (mean +/- SD) 120 +/- 78 in controls, and 210 +/- 190 in migraine patients (P = 0.046, t-test). Moreover, no control patient had a B(max)/K(D) ratio greater than 398, while three migraine patients had ratios of 417, 572 and 722, respectively. Ouabain binding is affected by Na/K ATPase structure (K(D)) and expression (B(max)). While these parameters were not altered in migraine with aura patients, the difference in their ratio suggests an imbalance between the enzyme's ouabain affinity and its expression, with higher-affinity subtypes being more expressed than normal. Moreover, single patients had values quite different from the control population. Our data suggest that (i) ouabain binding to lymphocyte membranes may be a useful tool in the diagnosis of migraine with aura and (ii) Na/K ATPase abnormalities may be involved in migraine aura.

Effects of purified endogenous inhibitor of the Na+/Ca2+ exchanger on ouabain-induced arrhythmias in the atria and ventricle strips of guinea pig

Previous studies demonstrated that the purified endogenous inhibitor (NCX(IF)) of the cardiac Na(+)/Ca(2+) exchanger (NCX1) has the capacity to modulate cardiac muscle contractility. Here, we tested the effects of purified NCX(IF) on arrhythmias induced by ouabain in the atria and ventricle strips of guinea pig. For the sake of comparison NCX(IF) was compared to lidocaine and KB-R7943. In the ventricle strip, NCX(IF) ( approximately 10 U/ml) results in rapid, complete and stable inhibition of ouabain-induced arrhythmias (the inhibition of arrhythmia is not followed by revival of irregular contractions). Under similar experimental conditions the atria strips require somewhat higher doses of NCX(IF) (25-50 U/ml) for complete suppression of arrhythmia. In the atria strip, NCX(IF) (10-25 U/ml) increases the threshold dose (1 microM) of ouabain for arrhythmia onset 2.2+/-0.5-fold (n=5, p<0.05) as well as prolongs the lag-phase for arrhythmia appearance 4.0+/-0.5-fold (n=5, p<0.01). The lag period for arrhythmia onset was also lengthened (2.0+/-0.4-fold) by NCX(IF) in the ventricle strips (n=6, p<0.002). At low frequency of pacing (1 Hz), all three tested substances, lidocaine, KB-R7943, and NCX(IF) can effectively suppress the ouabain-induced arrhythmia. However, at higher frequency (2 Hz), lidocaine is ineffective in suppressing arrhythmia, whereas KB-R7943 becomes pro-arrhythmic. In contrast to reference drugs, NCX(IF) retains its anti-arrhythmic capacity at high frequencies, either in the atria (n=6, p<0.01) or ventricle (n=5, p<0.05) strips. In conclusion, NCX(IF) results in rapid, effective and stable suppression of arrhythmia both in the atria and ventricle preparations under conditions at which the reference drugs become ineffective.

[Changes in renal sodium transport during hypertension development in ouabain-hypertensive rats]

OBJECTIVE

To investigate the changes in renal sodium transport during development of hypertension in ouabain-hypertensive rats (OHR) and further elucidate the role of ouabain in the pathogenesis of hypertension.

METHODS

Eighty male SD rats weighing 80-100 g were randomized equally into normal control and ouabain groups and treated with intraperitoneal injection of normal saline (1 ml/kg) and ouabain (27.8 microg/kg) once daily, respectively. Systolic blood pressure (SBP) and body weight of the rats were recorded weekly. One week before sacrifice scheduled at weeks 2, 4, 6 and 8, respectively, the rats were individually housed in metabolic cages to determine food consumption twice. Blood and 24-hour urine samples were collected to measure serum and urine concentration of sodium, trace lithium and creatinine. Endogenous creatinine clearance rate (Ccr), fractional excretions of sodium (FENa), fractional excretions of lithium (FELi) and fractional reabsorption of sodium in the distal tubules (FDRNa) were calculated.

RESULTS

The body weight and food intake between ouabain groups and control groups were comparable during the experiment (P>0.05). Blood pressure was also comparable in the two groups after 2 weeks (P>0.05). At week 4, however, blood pressure of ouabain group was significantly higher than that of the control group (P<0.001) and increased in a dose-dependent manner. The SBP in ouabain group appeared to reach a plateau at week 7. Ccr and plasma sodium (PNa) were similar in the 2 groups during the experiment (P>0.05). FELi was significantly lower at weeks 2, 4 and 6 in ouabain group than in the control group (P<0.01), and FELi decrement in ouabain group was accompanied by reduced sodium excretion. FENa was significantly lower at week 4 in ouabain group than in the control group (P<0.05), but this difference was not significant in weeks 2 and 6 (P>0.05). At weeks 2, 4 and 6, ouabain group showed significantly lower FDRNa than the control group (P<0.05), suggesting the compensation of the distal nephron segments. After 8 weeks, FENa, FELi and FDRNa were similar between the two groups (P>0.05).

CONCLUSIONS

Ouabain can increase renal proximal tubule reabsorption of sodium and consequently decrease renal sodium excretion in OHR, which can contribute to alteration of the pressure-natriuresis relationship in OHR, and play an important role in the development and maintenance of hypertension of OHR.

[Contribution of endothelin and its receptors to ouabain-induced hypertension in rats]

OBJECTIVE

To investigate the effect of endothelin and its receptors on ouabain-induced hypertension in rats.

METHODS

Male Sprague-Dawley (SD) rats were treated with ouabain or saline for 6 weeks and their systolic blood pressure (SBP) were recorded weekly. At the end of 2, 4 and 6 weeks, respectively, the plasma and left ventricle endothelin contents were measured by radio-immunoassay, and real-time quantitative RT-PCR was employed to determine the mRNA level of endothelin type A receptor (ETAR) and type B receptor (ETBR) in the left ventricle, and the protein expressions of ETAR and ETBR were examined by immuno-histochemistry.

RESULTS

After 4 weeks of intraperitoneal ouabain injection, the mean SBP in ouabain group increased till reaching a level significantly higher than that in the control group after 6 weeks (P<0.001). The plasma and left ventricle endothelin contents were significantly increased after 2 weeks of ouabain injection (P<0.01), and similarly, increased ETAR mRNA was observed. After 4 weeks of treatment, ETAR mRNA was increased continuously and the protein expression of ETAR upregulated in ouabain group as compared with the control group. The transcription and protein expression of ETBR were not altered by ouabain treatment.

CONCLUSION

Before detectable blood pressure elevation occurs, endothelin concentration and ETAR can be already upregulated in ouabain-induced hypertensive rats, suggesting that endothelin might be involved in the cardiovascular effects of ouabain via an action on ETAR.

The iodinated radiographic contrast medium iohexol mimics the vasodilator effect seen with small increases in extracellular K+ in the isolated rabbit central ear artery

PURPOSE

To investigate whether iodinated radiographic contrast media (IRCM) mimic the hyperpolarizing and vasodilator effects of K+ by comparing the vasodilator effect of a transient rise in extracellular K+ with that of the IRCM iohexol.

MATERIAL AND METHODS

Immersed rabbit central ear arterial rings with and without endothelium and pre-contracted with phenylephrine (PE) were used to investigate the dependency of the endothelium in K+-induced vasodilatation. Perfused rabbit central ear arteries, pre-contracted with PE, were used to study the effects of bolus administrations of the IRCM iohexol or KCl on arterial tone under conditions that mimic those employed during clinical arteriography.

RESULTS

A small rise in K+ caused an endothelium-independent and ouabain-sensitive relaxation of PE-constricted rabbit central ear artery rings. The relaxation was not changed in the presence of barium. The IRCM iohexol and KCl, injected as boluses into perfused PE-constricted rabbit ear arteries, caused transient decreases in perfusion pressure. Iohexol- and K+-induced pressure decreases were significantly reduced in the presence of 10 microM ouabain alone or in combination with 30 microM barium. Neither iohexol- nor K+-induced pressure decrease was significantly changed in the presence of barium alone compared to controls.

CONCLUSION

The vasodilator effect of IRCM mimics the vasodilator effect seen upon small increase in extracellular K+. Under the experimental conditions employed in the present study, a considerable part of the IRCM-induced vasodilatation appears to be due to activation of Na+/K+-ATPase in the smooth muscle cells.

Effects of a Na+/Ca2+ exchanger inhibitor on pulmonary vein electrical activity and ouabain-induced arrhythmogenicity

OBJECTIVE

Pulmonary veins (PVs) are the most important focus for generation of atrial fibrillation. The Na(+)/Ca(2+) exchange (NCX) current is important in PV electrical activity and cardiac glycosides-induced arrhythmias. The purpose of this study was to investigate whether KB-R7943, a NCX current blocker with preferential inhibition of the Ca(2+) influx, may alter PV electrophysiological characteristics and reduce glycoside-induced arrhythmogenicity.

METHODS

Conventional microelectrodes were used to record the effects of KB-R7943 on action potentials and contractility in isolated rabbit PV tissue specimens with and without administration of ouabain. The ionic currents and intracellular calcium were studied in isolated single cardiomyocytes before and after KB-R7943 by the whole-cell patch clamp and indo-1 fluorimetric ratio techniques.

RESULTS

KB-R7943 (0, 3, 10, 30 microM) concentration-dependently prolonged APD(50) and APD(90) and decreased the PV firing rates (2.3 +/- 1.2 Hz, 2.1 +/- 1.2 Hz, 1.9 +/- 0.9 Hz, 1.7 +/- 1.1 Hz, n = 7, p < 0.05) and incidences of delayed afterdepolarizations (DADs). KB-R7943 (3, 30 microM) decreased transient inward currents, Ca(2+) transient and sarcoplasmic reticulum Ca(2+) content. Ouabain (0, 0.1, 1 microM) concentration-dependently increased the PV firing rates and DADs in PVs with spontaneous activity (n = 7) and induced nonsustained spontaneous activity (1 microM) in the PVs without spontaneous activity (n = 14). However, in the presence of KB-R7943 (30 microM), ouabain (1 microM) did not increase the PV firing rates or induce spontaneous activity in the PVs without spontaneous activity (n = 7).

CONCLUSIONS

KB-R7943 reduces the PV arrhythmogenic activity and prevents the ouabain-induced arrhythmogenicity. Our findings support the role of the NCX current in the PV electrical activity.

Alterations in structure and mechanics of resistance arteries from ouabain-induced hypertensive rats

We have previously described that chronic administration of ouabain induces hypertension and functional alterations in mesenteric resistance arteries. The aim of this study was to analyze whether ouabain treatment also alters the structural and mechanical properties of mesenteric resistance arteries. Wistar rats were treated for 5 wk with ouabain (8.0 microg/day sc). The vascular structure and mechanics of the third-order branches of the mesenteric artery were assessed with pressure myography and confocal microscopy. Total collagen content was determined by picrosirius red staining, collagen I/III was analyzed by Western blot, and elastin was studied by confocal microscopy. Vascular reactivity was analyzed by wire myography. Internal and external diameters and cross-sectional area were diminished, whereas the wall-to-lumen ratio was increased in arteries from ouabain-treated rats compared with controls. In addition, arteries from ouabain-treated rats were stiffer. Ouabain treatment decreased smooth muscle cell number and increased total and I/III collagens in the vascular wall. However, this treatment did not modify adventitia and media thickness, nuclei morphology, elastin structure, and vascular reactivity to norepinephrine and acetylcholine. The present work shows hypotrophic inward remodeling of mesenteric resistance arteries from ouabain-treated rats that seems to be the consequence of a combination of decreased cell number and impaired distension of the artery, possibly due to a higher stiffness associated with collagen deposition. The narrowing of resistance arteries could play a role in the pathogenesis of hypertension in this model.

[Renal sodium handling in ouabain-hypertensive rats]

OBJECTIVE

To investigate renal sodium handling of ouabain-hypertensive rats and the role of renal sodium handling in pathogenesis of hypertension using endogenous trace lithium as a marker of proximal sodium reabsorption.

METHODS

Forty male Sprague-Dawley (SD) rats weighting 180-220 g were equally divided into normal control group and ouabain group randomly. Rats were infused with normal saline 1 ml/ (kg x d) or ouabain 27.8 microg/ (kg-d) intraperitoneally once a day respectively. Systolic blood pressure (SBP) and body weight were recorded weekly. Rats were sacrificed after 2 and 6 weeks respectively. Blood and 24 hour urine sample were collected to measure the serum and urinary concentration of sodium, potassium, trace lithium, and creatinine. Endogenous creatinine clearance rate (Ccr), fractional excretions of sodium (FE(Na)), and fractional excretions of lithium (FE(Li)), the ratios of urinary lithium to sodium (U(Li)/U(Na)), the ratios of urinary potassium to sodium (U(K)/U(Na)), and fractional reabsorption of sodium in the postproximal tubules (FDR(Na)) were also calculated. All were studied on their normal diet and ate salt freely.

RESULTS

Blood pressure had no significant difference in these two groups after 2 weeks (P > 0.05); After 4 weeks, however, blood pressure was significantly higher in ouabain group than in control group (P < 0.01). Body weight of rats had no significant difference during the experiment period (P > 0.05). Ccr and FE(Na) were similar in these 2 groups (P > 0.05). FE(Li), U(Li)/U(Na), U(K)/U(Na), and FDR(Na) of ouabain group were significantly lower than control group after 2 and 6 weeks (P < 0.05, P < 0.01, P < 0.001 respectively).

CONCLUSION

The reabsorption of sodium increases in the proximal tubule in ouabain-hypertensive rats, and such increase occurs before the development of hypertension. Therefore, increase of proximal reabsorption of sodium may be involved in the pathogenesis of ouabain-induced hypertension.

Mutation of Gly-94 in transmembrane segment M1 of Na+,K+-ATPase interferes with Na+ and K+ binding in E2P conformation

The importance of Gly-93 and Gly-94 in transmembrane segment M1 of the Na+,K+-ATPase for interaction with Na+ and K+ was demonstrated by functional analysis of mutants Gly-93-Ala and Gly-94-Ala. In the crystal structures of the Ca2+-ATPase, the corresponding residues, Asp-59 and Leu-60, are located exactly where M1 bends. Rapid kinetic measurements of K+-induced dephosphorylation allowed determination of the affinity of the E2P phosphoenzyme intermediate for K+. In Gly-94-Ala, the K+ affinity was reduced 9-fold, i.e., to the same extent as seen for mutation of the cation-binding residue Glu-329. Furthermore, Gly-94-Ala showed strongly reduced sensitivity of the E1P-E2P equilibrium to Na+, with accumulation of E2P even at 600 mM Na+, indicating that interaction of E2P with extracellular Na+ is impaired. On the contrary, in Gly-93-Ala, the affinity for K+ was slightly increased, and the E1P-E2P equilibrium was displaced in favor of E1P. In both mutants, the affinity of the cytoplasmically facing sites of E1 for Na+ was reduced, but this effect was relatively small compared with the effects seen for E2P in Gly-94-Ala. Comparison with Ca2+-ATPase mutagenesis data suggests that the role of M1 in binding of the transported ions is universal among P-type ATPases, despite the low sequence homology in this region. Structural modeling of Na+,K+-ATPase mutant Gly-94-Ala on the basis of the Ca2+-ATPase crystal structures indicates that the alanine side chain comes close to Ile-287 of M3, particularly in E2P, thus resulting in a steric clash that may explain the present observations.

Ion-motive ATPases and active, transbranchial NaCl uptake in the red freshwater crab, Dilocarcinus pagei (Decapoda, Trichodactylidae)

The present investigation examined the microanatomy and mRNA expression and activity of ion-motive ATPases, in anterior and posterior gills of a South American, true freshwater crab, Dilocarcinus pagei. Like diadromous crabs, the anterior gills of this hololimnetic trichodactylid exhibit a highly attenuated (2-5 microm), symmetrical epithelium on both lamellar surfaces. In sharp contrast, the posterior gill lamellar epithelia are markedly asymmetrical. Their proximal side consists of thick (18-20 microm) cells, displaying features typical of a transporting epithelium, while the distal epithelium is thin (3-10 microm) and formed entirely by apical pillar cell flanges. Both anterior and posterior gills express Na+/K+- and V-ATPases. Phylogenetic analysis of partial cDNA sequences for the Na+/K+-ATPase alpha-subunit and V-ATPase B-subunit among various crab species confirmed the previous classification and grouping of D. pagei based on morphological criteria. Semi-quantitative RT-PCR clearly showed that mRNA for both ion pump subunits is more intensely expressed in posterior gills. Na+/K+-ATPase activity in the posterior gills was nearly fourfold that of anterior gills, while V-ATPase and F-ATPase activities did not differ. A negative short-circuit current (Isc) was measured using the distal side of split, posterior gill lamellae, mounted in a modified Ussing chamber and perfused symmetrically with identical hemolymph-like salines. Although hemolymph-side ouabain did not affect this current, concanamycin significantly reduced Isc without altering preparation conductance, suggesting V-ATPase-driven Cl- absorption on the distal side of the posterior gill lamellae, as known to occur in diadromous crabs adapted to freshwater. These findings suggest that active Na+ uptake predominates across the thick proximal epithelium, and Cl- uptake across the thin, distal epithelium of the posterior gill lamellae.

Osmoregulatory physiology of pyloric ceca: regulated and adaptive changes in chinook salmon

Functions of the anatomically obvious, yet peculiar, pyloric ceca of the fish gut have been a source of conjecture for over two millennia since Aristotle hypothesized on digestive utilities. Here, we demonstrate regulated and adaptive changes in osmoregulatory physiology of ceca from chinook salmon (Onchorhynchus tshawytscha). Transfer of salmon from freshwater to seawater (both short- and long-term) significantly stimulated both fluid uptake from 5.1 to 8.3-9.3 microl/cm2/hr and also Na+/K+ -ATPase from 6.5 to 8.3-9.6 micromol/ADP/mg protein/hr. Similar changes were induced with implants of cortisol, which resulted in high physiological cortisol levels in plasma. Ceca, which can number about 200 in chinook salmon, were estimated to account for the majority of fluid uptake capacity of the intestine and, after long-term seawater adaptation, the proportion of uptake capacity was sixfold higher. Transport physiology of ceca is thus under environmental and endocrine control indicative of an important role in salt and water homeostasis.

A Model for Fluid Secretion in Rhodnius Upper Malpighian Tubules (UMT)

We have measured fluid secretion rate in Rhodnius prolixus upper Malpighian tubules (UMT) stimulated to secrete with 5-OH-tryptamine. We used double perfusions in order to have access separately to the basolateral and to the apical cell membranes. Thirteen pharmacological agents were applied: ouabain, Bafilomycin A(1), furosemide, bumetanide, DIOA, Probenecid, SITS, acetazolamide, amiloride, DPC, BaCl(2), pCMBS and DTT. These agents are known to block different ion transport functions, namely ATPases, co- and/or counter-transporters and ion and water channels. The basic assumption is that water movement changes reflect changes in ion transport mechanisms, which we localize as follows: (i) At the basolateral cell membrane, fundamental are a Na(+)-K(+)-2Cl(-) cotransporter and a Cl(-)-HCO(3) (-) exchanger; of intermediate importance are the Na(+)-K(+)-ATPase, Cl(-) channels and Rp-MIP water channels; K(+) channels play a lesser role: (ii) At the apical cell membrane, most important are a K(+)-Cl(-) cotransport that is being located for the first time, a V-H(+)-ATPase; and a Na(+)-H(+) exchanger; a urate-anion exchanger and K(+) channels are less important, while Cl(-) channels are not important at all. A tentative model for the function of the UMT cell is presented.

The alpha2-isoform of Na-K-ATPase mediates ouabain-induced hypertension in mice and increased vascular contractility in vitro

Although ouabain is known to induce hypertension, the mechanism of how this cardiac glycoside affects blood pressure is uncertain. The present study demonstrates that the alpha2-isoform of the Na-K-ATPase mediates the pressor effects of ouabain in mice. To accomplish this, we analyzed the effect of ouabain on blood pressure in wild-type mice, where the alpha2-isoform is sensitive to ouabain, and genetically engineered mice expressing a ouabain-insensitive alpha2-isoform of the Na-K-ATPase. Thus differences in the response to ouabain between these two genotypes can only be attributed to the alpha2-isoform of Na-K-ATPase. As the alpha1-isoform is naturally resistant to ouabain in rodents, it will not be inhibited by ouabain in either genotype. Whereas prolonged administration of ouabain increased levels of ouabain in serum from both wild-type and targeted animals, hypertension developed only in wild-type mice. In addition, bolus intravenous infusion of ouabain increased the systolic, mean arterial, and left ventricular blood pressure in only wild-type anesthetized mice. In vitro, ouabain increased vascular tone and thereby phenylephrine-induced contraction of the aorta in intact and endothelium-denuded wild-type mice but in alpha2-resistant mice. Ouabain also increased the magnitude of the spontaneous contractions of portal vein and the basal tone of the intact aorta from only wild-type mice. The increase in aortic basal tone was dependent on the presence of endothelium. Our studies also demonstrate that the alpha2-isoform of Na-K-ATPase mediates the ouabain-induced increase in vascular contractility. This could play a role in the development and maintenance of ouabain-induced hypertension.

Respiration rate of hepatocytes varies with body mass in birds

Hepatocytes were isolated from eight species of birds ranging from 13 g zebra finches to 35 kg emus. This represents a 2800-fold range of body mass (Mb). Liver mass (g) was allometrically related to species body mass by the equation: liver mass=19.6 x Mb(0.91). There was a significant allometric decline in hepatocyte respiration rate (HRR; nmol O2 mg(-1) dry mass min(-1)) with species body mass (kg) described by the relationship: HRR=5.27 x Mb(-0.10). The proportions of hepatocyte oxygen consumption devoted to (i) mitochondrial ATP production, (ii) mitochondrial proton leak and (iii) non-mitochondrial processes were estimated by using excess amounts of appropriate inhibitors. It was found that although hepatocyte respiration rate varied with body mass in birds, these processes constitute a relatively constant proportion of hepatocyte metabolic rate irrespective of the size of the bird species. The respective percentages were 54%, 21% and 25%. The portion of hepatocyte respiration devoted to ATP production for use by the sodium pump was estimated and found to be a relatively constant 24% of hepatocyte respiration and 45% of mitochondrial ATP production in different-sized bird species. These results are discussed in the context of competing theories to explain the metabolism-body size allometry, and are found to support the 'allometric cascade' model.

Basolateral ion transport mechanisms during fluid secretion byDrosophilaMalpighian tubules: Na+ recycling,Na+:K+:2Cl– cotransport and Cl– conductance

Mechanisms of ion transport during primary urine formation by the Malpighian tubule of Drosophila melanogaster were analyzed through measurements of fluid secretion rate, transepithelial ion flux, basolateral membrane potential (Vbl) and intracellular activities of K+ (aKi) and Cl–(aCli). Calculation of the electrochemical potentials for both ions permitted assessment of the possible contributions of K+ channels, Na+:K+:2Cl–cotransport, and K+:Cl– cotransport, to net transepithelial ion secretion across the basolateral membrane. The data show that passive movement of both K+ and Cl– from cell to bath is favoured across the basolateral membrane, indicating that both ions are actively transported into the cell. Contributions of basolateral K+ channels or K+:Cl– cotransporters to net transepithelial ion secretion can be ruled out. After prior exposure of tubules to ouabain, subsequent addition of bumetanide reduced fluid secretion rate, K+ flux and Na+ flux, indicating a role for a Na+:K+:2Cl– cotransporter in fluid secretion. Addition of the K+ channel blocker Ba2+ had no effect on aKi or aCli. Addition of Ba2+ unmasked a basolateral Cl– conductance and the hyperpolarization of Vbl in response to Ba2+ was Cl–-dependent. A new model for fluid secretion proposes that K+ and Cl– cross the basolateral membrane through a Na+-driven Na+:K+:2Cl–cotransporter and that most of the Na+ that enters the cells is returned to the bath through the Na+/K+-ATPase.

[Anti-arrhythmic effect of starfish sterol]

AIM

To study the effect of modified starfish sterol [C03, succinic acid (5-epiandroene-17-one-3beta-ol) diester] on experimental arrhythmias.

METHODS

Arrhythmias were induced by drugs (Aco, Oua, BaCl2 and adrenalin) i.v., ligating the left anterior descending coronary artery and electricity.

RESULTS

C03 71.4 mg x kg(-1) (ig) was shown to increase the dose of Oua inducing VP, VT, VF and CA in guinea pigs (P < 0.01); C03 (26.8, 80.4 mg x kg(-1)) was found to increase the dose of Aco inducing VF and CA in rats (P < 0.01); C03 (8.9, 26.8, 80.4 mg x kg(-1)) increase the dose of barium chloride and delay the onset time of ventricular arrhythmias (P < 0.01); C03 (14.1, 42.3 mg x kg(-10) shorten time of recovering induced by adrenalin in rabbits (P < 0.01); C03 (80.4 mg x kg(-1)) was shown to reduce the number of ventricular arrhythmias induced by coronary artery ligation in rats (P < 0.05), C03 increase VFT induced by electricity in rabbits, VFT of C03 14.1 mg x kg(-1) increased from (5.1 +/- 2.5) V to (11.0 +/- 2.7) V (P < 0.01), 42.3 mg x kg(-1) increased from (6.1 +/- 1.7) V to (15 +/- 5) V (P < 0.01).

CONCLUSION

Starfish sterol has anti-arrhythmic effect.

Cellular Potassium Ion Deprivation Enhances Apoptosis Induced by Cisplatin

The anticancer drug cisplatin induces cell death by apoptosis. Apoptosis is dependent on cellular loss of potassium ions (K+). We have recently shown that the antifungal drug amphotericin B (enhancing K+ efflux), combined with the Na+, K+, 2Cl(-)-cotransport blocker bumetanide (decreasing K+ influx), augmented cisplatin-induced apoptosis in vitro. We therefore quantified K+ fluxes with the K+ analogue rubidium (86Rb+) in cisplatin-induced apoptosis of mesothelioma cells treated with bumetanide and amphotericin B. Bumetanide combined with amphotericin B enhanced cisplatin-induced apoptosis by a pronounced initial reduction of K+ influx due (in addition to Na+, K+, 2Cl(-)-cotransport inhibition) also to Na+, K+, ATPase pump inhibition. As 86Rb+ efflux was initially preserved, combination of the drugs would lead to net K+ loss. Combinations of K+ flux modulators leading to cellular potassium ion deprivation thus augments cisplatin-induced apoptosis and could therefore possibly be used to enhance the antitumour efficacy of cisplatin treatment.

Ion transport in the intestine of Gobius niger in both isotonic and hypotonic conditions

Ion transport in the intestine of Gobius niger, a euryhaline teleost, was studied in both isotonic and hypotonic conditions. Isolated tissues, mounted in Ussing chambers and bilaterally perfused with isotonic Ringer solution, developed a serosa negative transepithelial voltage and a short circuit current indicating a net negative current in absorptive direction. Bilateral removal of Cl- and Na+ from the bathing solutions as well as the luminal removal of K+in the presence of Ba2+(10(-3) M) almost abolished both Vt and Isc. Similar results were obtained by adding bumetanide (10(-5)M) to the luminal bath while other inhibitors of Cl- transport mechanisms were ineffective. These observations suggest that salt absorption begins with a coupled entry of Na+, Cl-, and K+ across the apical membrane; a Ba2+inhibitable K+ conductance, demonstrated also by micropuncture experiments, recycles the ion into the lumen. Salt entry into the cell is driven by the operation of the basolateral Na+/K(+)-ATPase since serosal ouabain (10(-4)M) completely abolished both Vt and Isc; this pump also completes the Na(+) absorption. The inhibitory effect of both serosal bumetanide (10(-4)M) and SITS (5 x 10(-4)M) suggests that Cl- would leave the cell via the KCl cotransport, the Cl/HCO3- antiport and/or conductive pathways. Bilateral exposure of tissues to hypotonic media produced a reduction of both the transepithelial voltage and the short circuit current probably due to the activation of homeostatic ionic fluxes involved in cell volume regulation. The results of experiments with both isolated enterocytes and intestine exposed to hypotonic solution suggested that the recovery of cell volume, after the initial cell swelling, involves a parallel opening of K+ and Cl- channels to facilitate net solute and water effluxes from the cell. J. Exp. Zool. 301A:49-62, 2004.

Effects of class I antiarrhythmic drugs on the digitalis-induced triggered activity arrhythmia model: a rationale for the short-term use of class I drugs against triggered arrhythmias

Delayed afterdepolarization (DAD)-induced triggered activity has been considered to be one of the generation mechanisms of ventricular arrhythmias in the presence of intracellular Ca2+ overload. In this study, we analyzed the antiarrhythmic effects of class I antiarrhythmic drugs, namely, disopyramide, procainamide, mexiletine, and flecainide, on a recently developed DAD-induced triggered arrhythmia model, which consists of a canine ventricular septum preparation cross-circulated with a blood-donor dog. After intravenous administration of ouabain to the donor dog, triggered arrhythmias were consistently induced in the cross-circulated preparation by train stimulation (cycle length: 300 ms; train number: 15). Intracoronary administration of disopyramide, procainamide, mexiletine, and flecainide as well as lidocaine suppressed the triggered arrhythmias at clinically relevant doses. Similar doses have been demonstrated to suppress intraventricular conduction in the same experimental model. These results suggest that the Na+ channel inhibition by class I drugs is an effective pharmacological intervention for suppressing Ca2+ overload, which may provide a rationale for the short-term use of class I drugs against the triggered arrhythmias in clinical practice.

Regional distribution of Na,K-ATPase activity in porcine lens epithelium

PURPOSE

It has been established that Na,K-ATPase activity is higher in lens epithelium than fibers. However, others have suggested the Na,K-ATPase enzyme may be inactive or absent in the central 10% of the epithelium. Studies were conducted to measure and compare Na,K-ATPase specific activity and to examine Na,K-ATPase protein expression in the anterior and equatorial regions of porcine lens epithelium.

METHODS

Na,K-ATPase activity was determined by measuring the ouabain-sensitive rate of adenosine triphosphate (ATP) hydrolysis. Western blot analysis was used to detect Na,K-ATPase catalytic subunit (alpha) and glycoprotein subunit (beta) protein as well as beta-actin which was used as a loading control.

RESULTS

Na,K-ATPase specific activity was more than two times higher in the equatorial epithelium than the anterior 50% of the epithelium. However, the abundance of Na,K-ATPase alpha1 isoform protein was similar in the two regions. Neither the alpha2 nor alpha3 Na,K-ATPase isoform could be detected in the anterior or equatorial epithelium, but Na,K-ATPase beta1 protein was detected in both regions. In contrast to the observed regional difference in Na,K-ATPase activity, the activity of a different P-type ATPase, plasma membrane Ca-ATPase (PMCA), was not significantly different in the anterior and central epithelium. Western blot analysis indicated the presence of two PMCA isoforms, PMCA2, and PMCA4.

CONCLUSIONS

Na,K-ATPase activity is significantly higher at the equatorial region of the epithelium compared with the anterior, even though the level of Na,K-ATPase protein is similar in the two regions. It is possible that nonuniform distribution of functional Na,K-ATPase activity contributes to the driving force for circulating solute movement through the lens fiber mass.

Effect of citalopram on ouabain-induced arrhythmia in isolated guinea-pig atria

The effect of citalopram (CTP) a selective serotonin reuptake inhibitor agent was studied on ouabain-induced arrhythmia in spontaneously beating isolated guinea-pig atria. CTP (2-32 microg/ml) produced a dose-dependent decrease in the force of contractions (7-62%), and in the rate of contractions (11-72%). Pre-administration of the atria with CTP inhibited the ouabain-induced arrhythmia in isolated atria. Ouabain alone (1.2 microg/ml) produced arrhythmia at 4.5 min, and asystole at 20.7 min. Pretreatment with CTP (8 microg/ml) significantly increased the time of onset of arrhythmia to 9.5 min. In addition CTP prolonged the beating of atria (survival time) to more than 56 min, and inhibited the occurrence of asystole. These findings indicate that CTP produces direct cardiac action, probably due to the inhibition of cardiac Na(+) and Ca(2+) channels. Moreover our results suggest that CTP may reduce the membrane conductance through inhibition of ionic channels which decrease ouabain-induced arrhythmia.