Characteristics of neutralizing antibody titers of the SARS-CoV-2 vaccine in maintenance hemodialysis patients.

AIMS: Hemodialysis patients have high COVID-19 severity and mortality rates. For this high-risk group of hemodialysis patients with SARS-CoV-2 infection, early SARS-CoV-2 vaccination is recommended to prevent infection and severe disease. Thus far, few reports have evaluated COVID-19 antibody titers in hemodialysis patients. In this study, we investigated the time course of antibody titers acquired by vaccination in patients on dialysis. MATERIALS AND METHODS: The anti-SARS-CoV-2 spike protein S1 IgG (anti-SP-IgG) antibody titers were compared between 33 outpatient maintenance hemodialysis patients and 32 age- and sex-matched healthy subjects. Antibody tests were performed at five time points: 6 months after the 2nd vaccination, immediately before the 3rd vaccination (8 months after the 2nd vaccination), and 2 weeks, 1 month, and 3 months after the 3rd vaccination. RESULTS: The dialysis patient group had significantly lower values of anti-SP-IgG antibody titers than the control group 6 months after the 2nd vaccination (433.7 ± 36.24 vs. 650.2 (427.2 - 759.4) (AU/mL), p = 0.006) and immediately before the 3rd vaccination (219.3 (129.4 - 423.4) vs. 443.3 (267.1 - 600.4) (AU/mL), p = 0.034), but no significant differences were observed after the 3rd vaccination (19,000.0 (11,000.0 - 3,6000.0) vs. 23,500.0 (20,250.0 - 29,000.0) (AU/mL), p = 0.538). CONCLUSION: This study confirmed that patients undergoing hemodialysis were proven to have acquired sufficient antibody titers after the vaccination.

Characteristics of Month-by-Month Blood Pressure Variability in Patients on Hemodialysis.

INTRODUCTION: Poor prognosis in hemodialysis (HD) patients is due to the increased prevalence of cardiovascular diseases among them. We previously reported that higher visit-by-visit blood pressure variability is associated with increased cardiovascular mortality in HD patients. This present study aimed to investigate the characteristics of month-by-month blood pressure variability (MMBPV) in these patients. METHODS: A total of 324 maintenance HD patients, who could be followed up for 60 months, were recruited. We used standard deviation (SD), coefficient of variation (CV), and variation independent of the mean (VIM) in pre- and post-dialysis systolic blood pressure (pre- and post-SD, pre- and post-CV, and pre- and post-VIM) as an index of MMBPV. We investigated (1) the reproducibility of MMBPV, (2) relationship between these values and background factors, and (3) association between these values and mortality. RESULTS: MMBPV (pre- and post-SD, pre- and post-CV, and pre- and post-VIM) showed significant reproducibility (intraclass correlation, 0.483 [p < 0.001], 0.553 [p < 0.001], 0.450 [p < 0.001], 0.518 [p < 0.001], 0.456 [p < 0.001], and 0.522 [p < 0.001], respectively). High pre-VIM was associated with high interdialytic weight gain and poor nutritional status. High post-VIM was associated with glucose intolerance, high interdialytic weight gain, and poor nutritional status and associated with high rate of cardiovascular deaths independent of other factors (hazard ratio: 1.104, 95% confidence interval: 1.011-1.207, p = 0.028). CONCLUSION: These data suggested that pre- and post-VIM in HD patients are reproducible and associated with various background factors, and especially post-VIM is independently correlated with cardiovascular mortality. Further studies are necessary to confirm the mechanism of increased post-VIM and clarify whether reducing post-VIM can improve the prognosis of HD patients.

Modeling Low Muscle Mass Screening in Hemodialysis Patients.

INTRODUCTION: Computed tomography (CT) can accurately measure muscle mass, which is necessary for diagnosing sarcopenia, even in dialysis patients. However, CT-based screening for such patients is challenging, especially considering the availability of equipment within dialysis facilities. We therefore aimed to develop a bedside prediction model for low muscle mass, defined by the psoas muscle mass index (PMI) from CT measurement. METHODS: Hemodialysis patients (n = 619) who had undergone abdominal CT screening were divided into the development (n = 441) and validation (n = 178) groups. PMI was manually measured using abdominal CT images to diagnose low muscle mass by two independent investigators. The development group's data were used to create a logistic regression model using 42 items extracted from clinical information as predictive variables; variables were selected using the stepwise method. External validity was examined using the validation group's data, and the area under the curve (AUC), sensitivity, and specificity were calculated. RESULTS: Of all subjects, 226 (37%) were diagnosed with low muscle mass using PMI. A predictive model for low muscle mass was calculated using ten variables: each grip strength, sex, height, dry weight, primary cause of end-stage renal disease, diastolic blood pressure at start of session, pre-dialysis potassium and albumin level, and dialysis water removal in a session. The development group's adjusted AUC, sensitivity, and specificity were 0.81, 60%, and 87%, respectively. The validation group's adjusted AUC, sensitivity, and specificity were 0.73, 64%, and 82%, respectively. DISCUSSION/CONCLUSION: Our results facilitate skeletal muscle screening in hemodialysis patients, assisting in sarcopenia prophylaxis and intervention decisions.

Serum soluble (pro)renin receptor level as a prognostic factor in patients undergoing maintenance hemodialysis.

The (pro)renin receptor [(P)RR)] is a multifunctional protein that is cleaved to generate the soluble (P)RR [s(P)RR], reflecting the status of the tissue renin-angiotensin system and/or activity of the (P)RR. The serum s(P)RR level is associated with arteriosclerosis, independent of other risk factors, in patients undergoing hemodialysis (HD). This study was conducted to investigate whether the s(P)RR level was associated with new-onset cardiovascular events or malignant diseases and poor prognosis in patients undergoing HD. Overall, 258 patients [70 (61-76) years, 146 males] undergoing maintenance HD were prospectively followed up for 60 months. We investigated the relationships between s(P)RR levels and new-onset cardiovascular events/ malignant diseases and mortality during the follow-up period using Cox proportional hazard analyses. The cumulative incidence of new-onset cardiovascular events (P = 0.009) and deaths (P < 0.001), but not of malignant diseases, was significantly greater in patients with higher serum s(P)RR level (≥ 29.8 ng/ml) than in those with lower s(P)RR level (< 29.8 ng/ml). A high serum s(P)RR level was independently correlated with cardiovascular mortality (95% CI 1.001-1.083, P = 0.046). The serum s(P)RR level was associated with cardiovascular events and mortality, thus qualifying as a biomarker for identifying patients requiring intensive care.

Identification of a polyphenol and its antioxidant properties from the roasting reaction of alginic acid.

The radical scavenging activity of marine polysaccharides was enhanced by their high-temperature treatment (roasting reaction model). The product obtained from alginic acid exhibited maximum activity, and a radical scavenger, alginetin, was identified in the product. Its antioxidant activities were examined by chemical methods, which confirmed that it possessed a stoichiometrically greater antioxidant capacity than that of Trolox.

Bioactivity of alginetin, a caramelization product of pectin: Cytometric analysis of rat thymic lymphocytes using fluorescent probes.

Alginetin is the major product formed from pentoses and hexurionic acids. Alginetin is producted by cooking process of food including pection, a naturally-occurring polysacharride found in many plants. However, the biological interaction and toxicity of alginetin are not known at all. The aim of the present study was to investigate the cellular actions of alginetin on rat thymic lymphocytes. The effects of alginetin on the cell were examined using flow cytometry with fluorescent probes. Alginetin increased cellular content of non-protein thiols ([NPT]i) and elevated intracellular Zn2+ levels ([Zn2+]i). Chelation of intracellular Zn2+ reduced the effect of alginetin on [NPT]i, and chelation of external Zn2+ almost completely diminished alginetin-induced elevation of [Zn2+]i, indicating that alginetin treatment increased Zn2+ influx. Increased [NPT]i and [Zn2+]i levels in response to alginetin were positively correlated. Alginetin protected cells against oxidative stress induced by hydrogen peroxide and Ca2+ overload by calcium ionophore. It is considered that the increases in [NPT]i and [Zn2+]i are responsible for the cytoprotective activity of alginetin because NPT attenuates oxidative stress and Zn2+ competes with Ca2+. Alginetin may be produced during manufacturing of jam, which may provide additional health benefits of jam.

Association between serum soluble (pro)renin receptor level and worsening of cardiac function in hemodialysis patients: A prospective observational study.

The (pro)renin receptor ((P)RR) is cleaved to generate soluble (P)RR (s(P)RR), which reflects the status of the tissue renin-angiotensin system. Hemodialysis (HD) patients have a poor prognosis due to the increased prevalence of cardiovascular diseases. The present study aimed to investigate whether serum s(P)RR level is associated with the worsening of cardiac function in HD patients. A total of 258 maintenance HD patients were recruited and serum s(P)RR concentration was measured. Background factors in patients who survived (S group) and patients who died (D group) during the 12-month follow-up period and relationships between serum s(P)RR level and changes in cardiac function during the follow-up period in the S group were investigated. The median serum s(P)RR value at baseline was 29.8 ng/ml. Twenty-four patients died during the follow-up period. Cardiothoracic ratio, human atrial natriuretic peptide (hANP), brain natriuretic peptide (BNP), and E over e-prime were significantly higher in the D group. In the S group, changes in hANP or BNP were significantly greater in the higher serum s(P)RR group than in the lower serum s(P)RR group. High serum s(P)RR level was significantly correlated with changes in BNP, independent of other factors. High serum s(P)RR level was associated with increases in BNP, independent of other risk factors, suggesting that an increased expression of (P)RR may be associated with a progression of heart failure in HD patients and that serum s(P)RR concentration could be used as a biomarker for selecting patients requiring intensive care.

Triphenyltin disrupts intracellular Zn2+ homeostasis in rat thymic lymphocytes.

Triphenyltin (TPT), previously used as an agricultural fungicide and industrial antifoulant, is now considered an environmental pollutant. The effect of TPT on human health is concerning due to its presence as a contaminant in seafood. In this study, the changes in intracellular Zn2+ concentration ([Zn2+]i) and cellular content of nonprotein thiols ([NPT]i) induced by triphenyltin chloride (TPTCH), were measured in rat thymic lymphocytes. This was studied by flow-cytometry using the fluorescent probes FluoZin-3-AM and 5-chloromethylfluorescein diacetate (5-CMF-DA). Incubation with TPTCH, at 0.1 µM or more (up to 3 µM), increased [Zn2+]i in a concentration-dependent manner. The TPTCH-induced elevation in [Zn2+]i was due to the increase in membrane Zn2+ permeability and intracellular Zn2+ release. Incubation with TPTCH at 0.3 µM significantly increased [NPT]i levels, whereas the addition of an intracellular Zn2+ chelator had no effect on the same. TPT at higher concentrations (1 or 3 µM) reduced [NPT]i. TPT may disturb intracellular Zn2+ signaling in lymphocytes that disturbs cellular functions.

Conflicting actions of 4-vinylcatechol in rat lymphocytes under oxidative stress induced by hydrogen peroxide.

4-Vinylcatechol (4VC) has been identified as an aroma compound in roasted foods, especially coffee. It is also a component in traditional herbal medicines. This compound may be subconsciously ingested through foods and herbs. Recent experimental evidence has shown that 4VC possesses an antioxidative action. However, the antioxidative action of 4VC at cellular levels is not well characterized. The effects of 4VC (0.1-100 µM) were examined on rat thymic lymphocytes without and with oxidative stress induced by 300 µM hydrogen peroxide (H2O2). Cell treatment with 100 µM 4VC alone for 4 h significantly increased the population of dead cells. Thus, 4VC at 100 µM or above elicits cytotoxicity. However, 4VC at sublethal concentrations (1-10 µM) significantly attenuated the H2O2-induced increase in cell lethality in a concentration-dependent manner. While application of 10 µM 4VC slowed the process of cell death induced by H2O2, 4VC did not antagonize the H2O2-induced reduction of cellular nonprotein thiols. Although 4VC at 10 µM did not affect intracellular Ca2+ and Zn2+ levels, the agent potentiated the H2O2-induced increases in these levels. These actions of 10 µM 4VC are adverse to the cells under the oxidative stress. However, 10 µM 4VC partly attenuated the cell death induced by 100 nM A23187, a calcium ionophore. There are conflicting actions of 4VC at 1-100 µM on the cells under oxidative stress although the agent is used for an antioxidant. Thus, caution is required when using 4VC as a therapeutic agent.

Characteristics of visit-to-visit blood pressure variability in hemodialysis patients.

Visit-to-visit blood pressure variability (VVBPV) is an independent risk factor for cardiovascular morbidity and mortality in the general population. Hemodialysis (HD) patients have a poor prognosis due to an increased prevalence of cardiovascular disease. Intradialytic hypotension is associated with excess mortality, but whether VVBPV influences mortality is still unclear in HD patients. The present study aimed to investigate the characteristics of VVBPV in these patients. A total of 324 maintenance HD patients, who could be followed for 60 months, were recruited. We used variation independent of the mean (VIM) in pre-dialysis systolic blood pressure (pre-VIM-SBP) as an index of VVBPV. We investigated (1) the reproducibility of pre-VIM-SBP, (2) the relationship between pre-VIM-SBP and background factors, and (3) the association between pre-VIM-SBP and mortality. Pre-VIM-SBP showed significant reproducibility [intraclass correlation, 0.45 (P < 0.001)]. Higher pre-VIM-SBP was associated with less physical activity and worse left ventricular diastolic function. Higher pre-VIM-SBP was associated with a higher rate of cardiovascular deaths independent of other factors. These data suggest that VVBPV in HD patients is reproducible and associated with various background factors. VVBPV is independently correlated with cardiovascular mortality (hazard ratio: 1.166, 95% confidence interval: 1.030-1.320, P = 0.015). Further studies are necessary to confirm the mechanism of increased VVBPV and to clarify whether reducing VVBPV will improve the prognosis for HD patients.

Modification of cell vulnerability to oxidative stress by N-(3-oxododecanoyl)-L-homoserine-lactone, a quorum sensing molecule, in rat thymocytes.

N-(3-oxododecanoyl)-l-homoserine-lactone (ODHL), a quorum sensing molecule, affects intracellular Zn2+ concentration ([Zn2+]i) and cellular levels of nonprotein thiols ([NPT]i) of rat thymic lymphocytes, both of which are assumed to affect cell vulnerability to oxidative stress. Therefore, it is interesting to examine the effects of ODHL on the cells under oxidative stress. ODHL augmented the cytotoxicity of H2O2, but not calcium ionophore A23187. ODHL potentiated the H2O2-induced elevation of [Zn2+]i, wherein, it greatly attenuated the H2O2-induced increase in intracellular Ca2+ concentration. ODHL did not affect [NPT]i in the presence of H2O2. Therefore, we conclude that the elevation of [Zn2+]i is involved in the ODHL-induced potentiation of H2O2 cytotoxicity. Our findings suggest that ODHL modifies cell vulnerability to oxidative stress in host cells.

Membrane hyperpolarization and depolarization of rat thymocytes by azoxystrobin, a post harvest fungicide.

Azoxystrobin, a broad-spectrum fungicide, has been increasingly used in the agricultural industry. In Japan in 2018, azoxystrobin at five times the normal limit was detected in a shipment of Australian barley that had been used in food products. Therefore, the effects of azoxystrobin need to be carefully examined to predict potential adverse reactions in humans. In this study, the effects of azoxystrobin on the membrane potential and intracellular Ca2+ levels of thymocytes have been photochemically examined using flow cytometry. Azoxystrobin hyperpolarized plasma membrane potential. This hyperpolarization appeared to be due to the activation of Ca2+-dependent K+ channels, as both the removal of extracellular Ca2+ and addition of charybdotoxin attenuated the observed hyperpolarization. In the presence of quinine, an anti-malarial drug that blocks Ca2+-dependent K+ channels, azoxystrobin depolarized the membranes instead. Azoxystrobin increased intracellular Ca2+ levels in a concentration-dependent manner through the influx of extracellular Ca2+ and intracellular release of Ca2+, as confirmed by reduction in azoxystrobin-induced response in the absence of extracellular Ca2+. It appears likely that azoxystrobin at micromolar concentrations modifies membrane ion permeability in thymocytes. Since changes in membrane potential and intracellular Ca2+ levels occur during typical physiological lymphocyte responses, azoxystrobin may disturb lymphocyte function.

Intra-axonal Ca2+ mobilization contributes to triphenyltin-induced facilitation in glycinergic transmission of rat spinal neurons.

Triphenyltin (TPT) is an organotin compound causing environmental hazard to many wild creatures. Our previous findings show that TPT increases of the frequency of spontaneous glycinergic inhibitory postsynaptic currents (sIPSCs) in rat spinal neurons without changing the amplitude and 1/e decay time. In our study, the effects of 2-aminoethoxydiphenyl borate (2-APB), dantrolene sodium, and thapsigargin on sIPSC frequency were examined to reveal the contribution of intra-axonal Ca2+ mobilization by adding TPT. 2-APB considerably attenuated the TPT-induced facilitation of sIPSC frequency while dantrolene almost completely masked the TPT effects, suggesting that the TPT-induced synaptic facilitation results from the activation of both IP3 and ryanodine receptors on endoplasmic reticulum (ER) membrane, though inositol triphosphate (IP3) receptor is less sensitive to TPT. Thapsigargin itself significantly increased the sIPSC frequency without affecting the current amplitude and decay time. Successive addition of TPT could not further increase the sIPSC frequency in the presence of thapsigargin, indicating that thapsigargin completely masked the facilitatory action of TPT. Results suggest that TPT activates the IP3 and ryanodine receptors while TPT inhibits the Ca2+-pump of ER membranes, resulting in the elevation of intra-axonal Ca2+ levels, leading to the increase of spontaneous glycine release from synaptic vesicles.

Zinc-dependent and independent actions of hydroxyhydroquinone on rat thymic lymphocytes.

Coffee contains hydroxyhydroquinone (HHQ). HHQ is one of the by-products released during bean roasting. Therefore, it is important to elucidate the bioactivity of HHQ to predict its beneficial or adverse effects on humans. We studied zinc-dependent and independent actions of commercially procured synthetic HHQ in rat thymocytes using flow cytometric techniques with propidium iodide, FluoZin-3-AM, 5-chloromethylfluorescein diacetate, and annexin V-FITC. HHQ at 1050 µM elevated intracellular Zn2+ levels by releasing intracellular Zn2+. HHQ at 10 µM increased cellular thiol content in a zinc-dependent manner. However, HHQ at 30-50 µM reduced cellular thiol content. Although the latter actions of HHQ (30-50 µM) were suggested to increase cell vulnerability to oxidative stress, HHQ at 0.3-100 µM significantly protected cells against oxidative stress induced by H2O2. The process of cell death induced by H2O2 was delayed by HHQ, although both H2O2 and HHQ increased the population of annexin V-positive living cells. However, HHQ at 10-30 µM promoted cell death induced by A23187, a calcium ionophore. HHQ at 10-30 µM exerted contrasting effects on cell death caused by oxidative stress and Ca2+ overload. Because HHQ is considered to possess diverse cellular actions, coffee with reduced amount of HHQ may be preferable to avoid potential adverse effects.

Captan-induced increase in the concentrations of intracellular Ca2+ and Zn2+ and its correlation with oxidative stress in rat thymic lymphocytes.

Captan, a phthalimide fungicide, is considered to be relatively nontoxic to mammals. There is a possibility that captan affects membrane and cellular parameters of mammalian cells, resulting in adverse effects, because of high residue levels. To test the possibility, we examined the effects of captan on rat thymic lymphocytes using flow-cytometry with appropriate fluorescent probes. Treatment with 10 and 30 µM captan induced apoptotic and necrotic cell death. Before cell death occurred, captan elevated the intracellular concentrations of Ca2+ and Zn2+ and decreased the concentration of cellular thiol compounds. These captan-induced phenomena are shown to cause cell death and are similar to those caused by oxidative stress. Captan also elevated the cytotoxicity of hydrogen peroxide. Results indicate that 10 and 30 µM captan cause cytotoxic effects on mammalian cells. Despite no report on the significant environmental toxicity hazard of captan in humans, it may exhibit adverse effects, described above, on wild organisms.

Cytometrical analysis of the adverse effects of indican, indoxyl, indigo, and indirubin on rat thymic lymphocytes.

Many businesses thrive by producing health supplements from agricultural products, as exemplified by the production of functional (or health) foods using plants traditionally cultivated in rural areas. Dyes, such as indican, indigo, indoxyl, and indirubin, present in dye plants, possess antibacterial, antifungal, and antiproliferative activities. However, these effects may also lead to cytotoxicity. Thus, studies on normal mammalian cells are necessary to identify cytotoxicity and prevent adverse effects of functional foods that contain these dyes. In this study, the effects of indican, indigo, indoxyl, and indirubin were evaluated by flow cytometry using appropriate fluorescent probes in rat thymic lymphocytes. Among the dyes analyzed, indirubin exerted distinct cellular activities. Treatment with indirubin (10-30 µM) increased the population of shrunken dead cells. The side scatter, but not forward scatter, increased in indirubin-treated living cells. It increased the population of annexin V-bound living and dead cells and that of dead cells without annexin V. Indirubin elevated intracellular Ca2+, but not Zn2+ levels. The cellular content of superoxide anions increased and that of glutathione decreased. Indirubin depolarized the cellular plasma and mitochondrial membranes. It did not potentiate or attenuate the cytotoxicity of A23187 (Ca2+ overload) and H2O2 (oxidative stress). The results suggested that indirubin induces both apoptotic and non-apoptotic cell death. It may be difficult to predict and prevent the adverse effects of indirubin due to its diverse activities on normal mammalian cells. Therefore, indirubin should be removed from products that contain dye plant extracts.

Cellular adverse actions of dibromoacetonitrile, a by-product in water bacterial control, at sublethal levels in rat thymocytes.

The aim of this study was to investigate the effects of dibromoacetonitrile (DBAN), a by-product in water bacterial control, at sublethal concentrations on rat thymocytes, by using a cytometric technique with appropriate fluorescent dyes. By using this method, the possibility that DBAN induces cellular actions related to oxidative stress was assessed. DBAN reduced the content of cellular nonprotein thiols under Zn2+-free conditions. It elevated the intracellular level of Zn2+, being independent from external Zn2+. DBAN increased cell vulnerability to the cytotoxic action of hydrogen peroxide. These actions of DBAN were likely related to oxidative stress. DBAN is formed by the reaction of bromides and chlorinated oxidants during water disinfection. Hydrolysis of 2,2-dibromo-3-nitrilopropionamide, an antimicrobial used in hydraulic fracturing fluids for production of shale gas and oil, produces DBAN. Therefore, the concern regarding the levels of DBAN in industrial water systems is necessary to avoid the environmental risk to humans and wild mammals.

Some adverse actions of chlorothalonil at sublethal levels in rat thymic lymphocytes: Its relation to Zn2.

Chlorothalonil, a polychlorinated aromatic fungicide, is considered non-toxic to small mammals. However, chlorothalonil inactivates sulfhydryl enzymes and depletes cellular glutathione. Chlorothalonil increases intracellular Zn2+ concentration ([Zn2+]i) in mammalian cells possibly because intracellular Zn2+ is released via zinc-thiol/disulfide interchange. The effects of chlorothalonil at sublethal concentrations on the cellular content of nonprotein thiols ([NPT]i) and [Zn2+]i were examined using flow cytometry in rat thymocytes. Low concentrations (0.3-1 µM) of chlorothalonil increased, but high concentrations (3-10 µM) decreased [NPT]i. These effects of chlorothalonil were partly attenuated by an intracellular Zn2+ chelator. Chlorothalonil at 0.3-10 µM increased [Zn2+]i in a concentration-dependent manner, which was largely dependent on the release of intracellular Zn2+. Both the decrease in [NPT]i and increase in [Zn2+]i increase the vulnerability of cells to oxidative stress. Chlorothalonil at 1-10 µM potentiated the cytotoxicity of H2O2 (300 µM). It was also the case for 10 µM pentachloronitrobenzene, but not 10 µM pentachlorophenol. In conclusion, chlorothalonil at low (sublethal) micromolar concentrations is cytotoxic to mammalian cells under oxidative stress.

Effects of triphenyltin on glycinergic transmission on rat spinal neurons.

Glycine is a fast inhibitory transmitter like γ-aminobutyric acid in the mammalian spinal cord and brainstem, and it is involved in motor reflex, nociception, and neuronal development. Triphenyltin (TPT) is an organometallic compound causing environmental hazard to many wild creatures. Our previous findings show that TPT ultimately induces a drain and/or exhaustion of glutamate in excitatory presynaptic nerve terminals, resulted in blockage of neurotransmission as well as methylmercury. Therefore, we have investigated the neurotoxic mechanism how TPT modulates inhibitory glycinergic transmission in the synaptic bouton preparation of rat isolated spinal neurons using a patch clamp technique. TPT at environmentally relevant concentrations (3-300 nM) significantly increased the number of frequency of glycinergic spontaneous and miniature inhibitory postsynaptic currents (sIPSC and mIPSC) without affecting the current amplitude and decay time. The TPT effects were also observed in external Ca2+-free solution containing tetrodotoxin (TTX) but removed in Ca2+-free solution with both TTX and BAPTA-AM (Ca2+ chelator). On the other hand, the amplitude of glycinergic evoked inhibitory postsynaptic currents (eIPSCs) increased with decreasing failure rate (Rf) and paired pulse ratio (PPR) in the presence of 300 nM TPT. At a high concentration (1 µM), TPT completely blocked eIPSCs after a transient facilitation. Overall, these results suggest that TPT directly acts transmitter-releasing machinery in glycinergic nerve terminals. Effects of TPT on the nerve terminals releasing fast transmitters were greater in the order of glycinergic > glutamatergic > GABAergic ones. Thus, TPT is supposed to cause a strong synaptic modulations on glycinergic neurotransmission in wild creatures.

Hyperpolarization by N-(3-oxododecanoyl)-l-homoserine-lactone, a quorum sensing molecule, in rat thymic lymphocytes.

To study the adverse effects of N-(3-oxododecanoyl)-l-homoserine-lactone (ODHL), a quorum sensing molecule, on mammalian host cells, its effect on membrane potential was examined in rat thymic lymphocytes using flow cytometric techniques with a voltage-sensitive fluorescent probe. As 3-300 µM ODHL elicited hyperpolarization, it is likely that it increases membrane K+ permeability because hyperpolarization is directly linked to changing K+ gradient across membranes, but not Na+ and Cl- gradients. ODHL did not increase intracellular Ca2+ concentration. ODHL also produced a response in the presence of an intracellular Zn2+ chelator. Thus, it is unlikely that intracellular Ca2+ and Zn2+ are attributed to the response. Quinine, a non-specific K+ channel blocker, greatly reduced hyperpolarization. However, because charybdotoxin, tetraethylammonium chloride, 4-aminopyridine, and glibenclamide did not affect it, it is pharmacologically hypothesized that Ca2+-activated K+ channels, voltage-gated K+ channels, and ATP-sensitive K+ channels are not involved in ODHL-induced hyperpolarization. Although the K+ channels responsible for ODHL-induced hyperpolarization have not been identified, it is suggested that ODHL can elicit hyperpolarization in mammalian host cells, disturbing cellular functions.