Bothrops jararacussu snake venom decreases CD1d, CD83, and CD86 expression on bone marrow-derived dendritic cells.

This study was designed to characterize mice bone marrow (BM) and bone marrow-derived dendritic cells (BMDC) and to compare the surface markers expression and inflammatory cytokine liberation in response to LPS and Bothrops jararacussu venom (BjV) stimulation. Typical morphology was observed in BM and BMDCs from the 4th up to the 8th day of culture using recombinant mouse GM-CSF and IL-4. A high basal level of MHC-II, CD1d, CD83, CD11c, CD80, and low CD86 was expressed by BM cells. After stimulation with GM-CSF/IL-4 for BMDCs differentiation, the BM cells differentiated into BMDCs presented MHC-II, CD1d, CD83, CD11c, CD86, and CD80 expression on the 4th - 8th day accompanied with high levels of TNF-α liberated. The difference between the surface markers' expression was observed in this time course in which CD1d, CD11c, and CD80 remained in high levels of expression, while MHC-II and CD83 showed moderate expression during the differentiation period. Also, cytokines liberation was monitored over the period of the BMDCs culture, and on the 6th day, low levels of IL-6 and IL-1ß were found, while high levels of TNF-α on the 4th and 8th days, both of which contributed to the maturity of the BMDCs. Maturation of DCs with LPS showed significant upregulation of surface markers (MHC-II, CD1d, CD83, CD86, CD80) and pro-inflammatory cytokines (IL-1ß, IL-6, TNF-α) liberation. On the other hand, BjV induced a decrease in CD1d, CD11c, CD83, and CD86 expression in mature BMDCs which was not observed when LPS was used to stimulate BMDCs which probably induces impairment in T-cell activation.

Complex interactions between nicotine and resveratrol in the Drosophila melanogaster wing spot test.

Nicotine (NIC) and resveratrol (RES) are chemicals in tobacco and wine, respectively, that are widely consumed concurrently worldwide. NIC is an alkaloid known to be toxic, addictive and to produce oxidative stress, while RES is thought of as an antioxidant with putative health benefits. Oxidative stress can induce genotoxic damage, yet few studies have examined whether NIC is genotoxic in vivo. In vitro studies have shown that RES can ameliorate deleterious effects of NIC. However, RES has been reported to have both antioxidant and pro-oxidant effects, and an in vivo study reported that 0.011 mM RES was genotoxic. We used the Drosophila melanogaster wing spot test to determine whether NIC and RES, first individually and then in combination, were genotoxic and/or altered the cell division. We hypothesized that RES would modulate NIC's effects. NIC was genotoxic in the standard (ST) cross in a concentration-independent manner, but not genotoxic in the high bioactivation (HB) cross. RES was not genotoxic in either the ST or HB cross at the concentrations tested. We discovered a complex interaction between NIC and RES. Depending on concentration, RES was protective of NIC's genotoxic damage, RES had no interaction with NIC, or RES had an additive or synergistic effect, increasing NIC's genotoxic damage. Most NIC, RES, and NIC/RES combinations tested altered the cell division in the ST and HB crosses. Because we used the ST and HB crosses, we demonstrated that genotoxicity and cell division alterations were modulated by the xenobiotic metabolism. These results provide evidence of NIC's genotoxicity in vivo at specific concentrations. Moreover, NIC's genotoxicity can be modulated by its interaction with RES in a complex manner, in which their interaction can lead to either increasing NIC's damage or protecting against it.

Cytokines and growth factors in a biologic product obtained from patients' urine as immune-modulators to treat autoimmune and allergic diseases.

At "Instituto de Alergias y Autoinmunidad Dr. Maximiliano Ruiz Castañeda, A.C." in Mexico City, a non-traditional health care center focused on the treatment of autoimmune and allergic diseases using personalized medicine, an alternative treatment referred to as an "immune-modulator" has been developed. In this study, we will refer to this treatment substance as the "immune-modulator." In brief, a urine sample is collected from the patient and processed to obtain the peptide fraction, which is conditioned and then administered sublingually to the patient. Sample processing involves multiple steps aimed at the removal of toxic compounds and enrichment for cytokines, growth factors, and other immune peptides that may contribute to the function of the immune-modulator. This treatment has been administered for many years, and patients testify that it is useful and reliable. Despite the benefits of this treatment, the molecular mechanisms underlying its effects have not been thoroughly investigated. Therefore, this study aims to identify immunoregulatory peptides, such as cytokines and growth factors, in the immune-modulator. Urine and immune-modulator concentrations of cytokines and growth factors were assessed using a Luminex assay. Twenty-one cytokines and growth factors were identified in immune-modulator samples. MCP-1 was identified in 100% of the samples; MIP-1ß, IL-8, RANTES, INF-γ, and IP-10 were identified in approximately 65-70% of samples; IL5, IL-1B, and IL-17 in 50-60%; eotaxin, VEGF, IL-6, and FGF in about 40%; MIP-1α, IL-9, GM-CSF, G-CSF, IL-12, and IL-15 in about 20-30%; and IL-13 and PDGF-bb were identified in <6% of samples. Additionally, patients exhibited significant changes in IL-1ß, IFN-γ, and MCP-1 concentrations after treatment with the immune-modulator, whereas healthy individuals showed no significant change in response to the treatment. The immune-modulator is an alternative treatment based on the administration of cytokines and growth factors obtained from the urine of patients. In this study, its composition was characterized. The isolated products could be responsible for the effects of the immune-modulator. Further trials are required to evaluate the effective delivery of these molecules by the administration route described.

Ultrafast laser welding of ceramics.

Welding of ceramics is a key missing component in modern manufacturing. Current methods cannot join ceramics in proximity to temperature-sensitive materials like polymers and electronic components. We introduce an ultrafast pulsed laser welding approach that relies on focusing light on interfaces to ensure an optical interaction volume in ceramics to stimulate nonlinear absorption processes, causing localized melting rather than ablation. The key is the interplay between linear and nonlinear optical properties and laser energy-material coupling. The welded ceramic assemblies hold high vacuum and have shear strengths comparable to metal-to-ceramic diffusion bonds. Laser welding can make ceramics integral components in devices for harsh environments as well as in optoelectronic and/or electronic packages needing visible-radio frequency transparency.

[Acute traumatic pectoralis major tendon ruptures. Case series with a new approach]. / Desinserción distal del pectoral mayor traumática aguda. Reporte de 19 casos con nuevo abordaje.

INTRODUCTION: Described for the first time in 1822, being the treatment in acute the method of choice since the chronic injuries results in more complex procedures by the presence of fibrosis and muscular retraction. MATERIAL AND METHODS: Report of 19 cases with injury after physical activity, averaging age 30 years and range 20-48 years. Average follow-up of 41 months, carrying out functional evaluations pre and post-operatively of CONSTANT, UCLA, SST and ASES, immobilization in internal rotation for five weeks. RESULTS: They showed improvement in the scales SST, CONSTANT, UCLA and ASES, being made with the U of Mann-Whitney for related samples, stablishing the value of p in 0.05 in all tests. CONSTANT preoperative values range from 32 to 93, UCLA ranges from 10 to 34, aces from 11.6 to 80 and SST from 0 to 9; CONSTANT postoperative values ranging from 73 to 96, UCLA with a range of 15 to 35, ASES with a range of 55 to 100 and SST ranging from 6 to 12. DISCUSSION: The use of this technique presented functional results, we consider has low level of difficulty, low risk of neurovascular injury, cosmetic and present functional recovery.

INTRODUCCIÓN: Descrita por primera vez en 1822, siendo el tratamiento en agudo el de preferencia, ya que el tardío resulta en procedimientos más complejos por la presencia de fibrosis y retracción muscular. MATERIAL Y MÉTODOS: Reporte de 19 casos con lesión posterior a actividad física, con un promedio de edad de 30 años y rango de 20-48 años de edad, con un seguimiento promedio de 41 meses, se realizaron evaluaciones funcionales pre- y postoperatoriamente de CONSTANT, UCLA, SST y ASES, inmovilización en rotación interna por cinco semanas. RESULTADOS: Presentaron mejoría evaluada con las escalas SST, CONSTANT, UCLA y ASES, se realizaron comparaciones con U de Mann-Whitney para muestras relacionadas, fijándose el valor de p en 0.05 en todas las pruebas. Valores preoperatorios CONSTANT rango de 32 a 93, UCLA rango de 10 a 34, ASES de 11.6 a 80 y SST de 0 a 9; valores postoperatorios CONSTANT con rango de 73 a 96, UCLA con rango de 15 a 35, ASES con rango de 55 a 100 y SST con rango de 6 a 12. DISCUSIÓN: El uso de esta técnica arrojó resultados funcionales, consideramos que tiene bajo nivel de dificultad, bajo riesgo de lesión neurovascular, cosmético y presenta recuperación funcional.

Lycopene, resveratrol, vitamin C and FeSO4 increase damage produced by pro-oxidant carcinogen 4-nitroquinoline-1-oxide in Drosophila melanogaster: Xenobiotic metabolism implications.

4-nitroquinoline-1-oxide (4-NQO) is a pro-oxidant carcinogen bioactivated by xenobiotic metabolism (XM). We investigated if antioxidants lycopene [0.45, 0.9, 1.8 µM], resveratrol [11, 43, 172 µM], and vitamin C [5.6 mM] added or not with FeSO4 [0.06 mM], modulate the genotoxicity of 4-NQO [2 mM] with the Drosophila wing spot test standard (ST) and high bioactivation (HB) crosses, with inducible and high levels of cytochromes P450, respectively. The genotoxicity of 4-NQO was higher when dissolved in an ethanol - acetone mixture. The antioxidants did not protect against 4-NQO in any of both crosses. In the ST cross, resveratrol [11 µM], vitamin C and FeSO4 resulted in genotoxicity; the three antioxidants and FeSO4 increased the damage of 4-NQO. In the HB cross, none of the antioxidants, neither FeSO4, were genotoxic. Only resveratrol [172 µM] + 4-NQO increased the genotoxic activity in both crosses. We concluded that the effects of the antioxidants, FeSO4 and the modulation of 4-NQO were the result of the difference of Cyp450s levels, between the ST and HB crosses. We propose that the basal levels of the XM's enzymes in the ST cross interacted with a putative pro-oxidant activity of the compounds added to the pro-oxidant effects of 4-NQO.

Interactions of sulforaphane and dimethyl sulfoxide with methyl methanesulfonate, urethane, 4-nitroquinoline-1-oxide and hydrogen peroxide in the Drosophila melanogaster wing spot test.

Sulforaphane (SF) is an isothiocyanate present in Brassicaceae, vegetables that induce the detoxification of electrophiles and reactive oxygen species. SF has been correlated with chemoprevention mechanisms against degenerative diseases. We tested if the SF had an effect against methyl methanesulfonate (MMS), urethane (URE), 4-NQO and H(2)O(2). SF (>95% purity, 0.14, 0.28, 0.56 mM) was diluted in a DMSO/Tw80/EtOH mixture (DTE) corresponding to 25, 50, 100% of lyophilized broccoli. The SF treatment (0.14 mM) was positive for small spots in the ST cross and negative in the HB cross. In the HB cross, SF (0.28 mM) was genotoxic. In the ST cross, the SF treatments showed a tendency to reduce the genotoxic damage caused by MMS, which could be explained by the radical scavenging action of the DTE mixture. In the ST cross, the frequency of small spots in the SF 0.14 mM/URE treatment was similar to that of Water/URE, which can be explained by a DTE and SF scavenger action. In both crosses, the results for the direct oxidants, 4-NQO and H(2)O(2), were different and must be related to differential modulation of CYPs expression and the SF and DTE scavenger properties.

Effect of milk minerals on calf gains and sex differences in mineral composition of milk from Iberian red deer (Cervus elaphus hispanicus).

Milk mineral content has received little attention in studies focusing on milk nutrient effects on offspring growth. This study examines calf growth in Iberian deer and compares the influence of milk minerals, other nutrients, and lactation variables relevant for growth to discern the relative weight of each factor. In addition, because Iberian deer hinds are the first mammal found to produce different milk for sons and daughters, the present study examines whether there are also sex differences in milk mineral composition. Concentrations and yields of Ca, P, Mg, Na, K, Fe, and Zn in milk of 46 red deer hinds were monitored through 18 weeks of lactation. Calf growth was influenced by Ca and P percent, and total Fe production. Milk for males had a lower content in Ca and P, a greater content of K, and Mg, whereas no sex effects were found in Na, Fe, or Zn percentages. Higher percentages in Ca and P for daughters might constitute a compensatory response, as daily production was not biased towards females in Ca or P, whereas in the latter and all the other minerals daily production was greater for heavier calves, which are usually males. In conclusion, milk mineral content and production influence calf growth even after controlling for other important lactation variables and nutrients, and they show effects and interactions more complicated than expected.

Seasonal changes in plasma leptin concentration related to antler cycle in Iberian red deer stags.

The aim of this study is to describe the leptin cycle in male Iberian red deer (Cervus elaphus hispanicus) and relate it to antler and testosterone cycles. An additional aim is to assess the relationship between the plasma leptin concentration during antlers' growth and their final size. Therefore, blood from 21 Iberian red deer males was sampled monthly to analyse leptin and testosterone. At the same time the deer were weighed and their body condition was assessed. The length of antlers was measured every 2 weeks and, after casting, their final length and perimeters were taken. Leptin showed a seasonal cycle, with a peak in June that decreased as testosterone increased. Low values were observed in autumn, winter and early spring. The relationship observed between leptin and body mass or body condition score was different in spring, when plasma testosterone concentration is low, than in autumn, when testosterone increases. Leptin peak amplitude was positively related to final antler size. In conclusion, the relationship between leptin and body mass and body condition score changes through the year, possibly due to the influence of androgens and photoperiod. There was a positive relationship between plasma concentration of leptin during antler growth and final antler length.

E-cadherin expression during urothelial carcinogenesis induced by N-butyl-N-(4-hydroxybutyl) nitrosamine in rats.

An alteration in the expression of E-cadherin has been observed in many epithelial neoplasms. No data exist, however, for the expression of this protein in an animal model for urinary bladder cancer. The present study investigated the expression of E-cadherin in rat urothelial preneoplastic lesions and tumours induced by oral administration of N-butyl-N-(4-hydroxybutyl) nitrosamine, during 10, 15 and 20 weeks. Simple hyperplasia and squamous metaplasia showed a similar E-cadherin pattern when compared with normal urothelium, with its expression confined to cell membrane. Thirty eight percent of the nodular hyperplasia, 41.4% of the dysplasia and 100% of the papillomas showed a weak E-cadherin expression. All papillary neoplasm of low malignant potential, low-and high-grade papillary carcinoma, and invasive carcinoma revealed an abnormal staining pattern with an increase in cytoplasm reactivity and discontinuous cell membrane positivity. The loss of expression for low-grade papillary carcinoma versus simple hyperplasia, nodular hyperplasia and dysplasia was statistically significant (p = 0.0001, p = 0.007 and p=0.008, respectively). There was a similar decrease in E-cadherin expression for papillary neoplasm of low malignant potential versus simple hyperplasia, nodular hyperplasia and dysplasia (p = 0.0001; p = 0.001 and p=0.0001, respectively). These results suggest that alteration in the expression of this adhesion molecule in rat may be indicative of tumour progression in N-butyl-N-(4-hydroxybutyl) nitrosamine-induced bladder cancer.

Leptin, reproduction and sex steroids.

Leptin is a hormone secreted mainly by the adipose cells with a primary role in the regulation of body weight by establishing a feedback loop between the energy reserves and the hypothalamic centers that control food intake. Recent data suggest that, in addition, leptin interacts with other endocrine systems to provide critical information about the size of the fat stores, acting as a permissive factor that allows the triggering of energy-demanding situations, as the onset of puberty and the reproduction, only when the size of the fuel reserve is large enough to guarantee its success. In addition, leptin appears to play a role during pregnancy and lactation, as it is produced by the placenta and is present in maternal milk. The fact that leptin levels are always higher in females, even after correcting for body fat content, suggests that the interaction between the adipose tissue and the reproductive system is modulated in a different way in males and females by androgenic and estrogenic hormones. In fact, adipose tissue samples taken from male donors are completely refractory in vitro to the action of both estrogens and androgens. On the contrary, dihydrotestosterone, androstenedione and dehydroepiandrosterone-S are potent inhibitors of leptin secretion, while estradiol induces a strong stimulation in adipose tissue taken from women. Testosterone is devoid of activity in either gender.

Dual effect of insulin on in vitro leptin secretion by adipose tissue.

Although it is widely accepted that insulin stimulates leptin secretion, a dual action was observed using a validated in vitro system, i.e., an early (less than 48 h) inhibitory action, followed later (48-96 h) by a clear-cut stimulation. While the inhibitory phase was observed at every glucose concentration tested (from 1 to 25 mM), the stimulatory phase required the presence of physiological or supraphysiological glucose concentrations. In fact, leptin secretion was virtually eliminated in the presence of glucose uptake inhibitors. This dual effect of insulin was not due to modifications of the ob mRNA levels, suggesting that it depends entirely on posttranslational mechanisms. In conclusion, insulin appears to induce an early inhibition of leptin secretion by the adipose cell, followed later by a stimulatory effect secondary to the metabolic changes triggered by the insulin-induced increase in glucose uptake.

GHRP-6 in heifer and cow adenohypophisial cells separated by elutriation.

Previous studies have reported that the growth hormone (GH)-releasing peptide (GHRP-6), a synthetic Met-enkephalin peptide analog, stimulates GH release in vivo in a variety of species, including bovine. In the present study, the in vitro effects of GHRP-6 on bovine somatotropes separated by elutriation were analyzed as well as its interactions with the GH-releasing hormone (GHRH). The administration of GHRP-6 at doses from 10(-8) M to 10(-5) M stimulated GH release, and also 10(-9) M in cow pituitary cells, and produced maximal stimulation at 10(-6) M. The effects of GHRP-6 (10(-6) M) on GH release were shown at 1, 2, 3 and 4-h incubation (p < 0.05), except for heifer pituitary cells at 1-h incubation (p > 0.05). The GH releasing effects of either GHRH alone or GHRH+GHRP-6 were significantly more potent than that of GHRP-6 alone (p < 0.05). Contrary to what occurred in rat pituitary cells, the combined administration of 10(-6) M GHRP-6 with 10(-8) M GHRH did not result in a synergist action of GH release. Although the additive effect was significant when compared with GHRH alone (p < 0.05). The results demonstrate the existence of differences in the effect of GHRH+GHRP-6 on bovine somatotropes. These differences may reflect the physiological importance of distinct cell subpopulation, like the mammosomatotroph cells.

Effect of growth hormone-releasing peptide 1-6 on GH secretion-stimulated by GHRH and pyridostigmine in lambs.

The GHRP-6 seems to act at a pituitary site, activating different intracellular messenger pathways from those utilized by GHRH, and at the hypothalamic level where receptors for GHRP-6 have been demonstrated. This study examines the effect of GHRP-6 on GH secretion in vitro and in vivo. Lamb adenohypophysial cell cultures were subjected to a challenge with 1) 10 nM GHRH-1-29; 2) 1 microM GHRP-6; and 3) 10 nM GHRH plus 1 microM GHRP-6. Both peptides released GH, GHRP-6 being less potent than GHRH, and the GH response to GHRH and GHRP-6 not being synergistic, without statistically significant differences between GHRH+GHRP-6 and GHRH alone. In in vivo studies, six lambs received 15 microg/kg GHRH (1-29) or 15 microg/kg GHRH plus 10 microg/kg GHRP-6 and six other lambs received 100 microg/kg GHRP-6 or 3 mg/kg pyridostigmine plus 100 microg/kg GHRP-6. The results have shown that the combination of GHRH plus GHRP-6, at low doses, causes higher GH peak (p < 0.05) and higher GH area under curve (p < 0.05) with respect to administration of GHRH alone. The administration of GHRP-6 plus pyridostigmine produced in a stronger GH response to GHRP-6 (100 microg/kg) in the amplitude of the GH peak (p < 0.001) and in the area under the GH response curve (p < 0.001). The complementary interactions of GHRP-6 with GHRH or pyridostigmine in releasing GH seem to indicate independent actions of these compounds. These results suggest that GHRP-6 potentiates the GH secretion stimulated by GHRH at the hypothalamic level, in these animals.

Simultaneous localization of Pit-1 protein and gonadotropins on the same cell type in the anterior pituitary glands of the rat.

Pit-1 is a prototypic member of the POU transcription factor family and plays a critical role in pituitary-specific action of growth hormone (GH), prolactin (PRL), and thyroid-stimulating hormone (TSH) beta-subunit genes. The purpose of the present study was to elucidate the changes in the expression of the Pit-1 product in the pituitary of pregnant rats employing an improved double-immunohistochemical method. The positive cells showed nuclear immunoreactivity and Pit-1 protein was frequently observed in the nuclei of many cells which were also immunopositive for GH, PRL, and betaTSH. Unexpectedly, a significant number of pituitary cells containing both Pit-1 and gonadotropins were also observed. These cells were usually distributed near blood vessels that supply the pituitary. While a prominent increase in the percentage of Pit-1/PRL, Pit-1/beta-luteinizing hormone and Pit-1/beta-follicle-stimulating hormone immunoreactive cells was observed in pregnant rats, the percentage of Pit-1/GH immunoreactive cells was strongly decreased. In contrast, no significant differences in the percentage of Pit-1/betaTSH doubly immunolabeled cells were noticed. Our findings strongly support the hypothesis that PRL could coexist in the Pit-1 immunopositive gonadotropes. Although Pit-1 protein was not detected in the nuclei of corticotropes, the existence of these cells in the rat pituitary cannot be excluded.

Effects of acute administration of growth hormone-releasing hormone (GHRH) and oxytocin on somatotroph cells in sheep: morphometric study and growth hormone (GH) secretion.

In this work, the combined use of the morphometric study of somatotroph cells and plasma GH levels provided new data for the interpretation of the role played by OT and GHRH on GH cells. GHRH 1-29 (15 micrograms/kg), oxytocin (2.5 IU animal) or 1 ml saline solution were administered to male lambs. The GH plasma concentration was measured by RIA and for the morphometric study the cellular area, nuclear area and volume density of the somatotroph cells were measured in 1 micron semi-thin sections immunolabeled with avidin-biotin technique (ABC). The area under the GH response curve for 3 hours after injection was similar in both saline and OT-treated animals (24.8 +/- 9.1 and 31.4 +/- 14.7 micrograms/ml, respectively) and much lower than that observed in GHRH-treated animals (445.5 +/- 126.7 micrograms/ml). The cell area of somatotrophs was smaller in the GHRH-treated lambs and larger in the OT-treated lambs than in the control lambs (71.47 +/- 1.56, 91.42 +/- 1.72 and 83.1 +/- 1.74 microns 2, respectively). A similar change was observed in the nuclear area; it decreased in the GHRH-treated lambs (21.61 +/- 0.52 microns 2) and increased in the OT-treated lambs (25.45 +/- 0.68 microns 2) with respect to the control group (23.75 +/- 0.44 microns 2). No significant differences were found in volume density.(ABSTRACT TRUNCATED AT 250 WORDS)

Altered levels of tissue and urinary prostacyclin in rats subjected to pancreas transplantation.

Significant increases of TXB2 and PGE2 are reported to occur in pancreas transplantation. These increases are prevented with scavengers of oxygen-free radicals. In this communication, we report on changes of prostacyclin metabolites such as tissue 6-keto prostaglandin F1 alpha and urinary 2,3-dinor 6-keto prostaglandin F1 alpha in rats subjected to pancreas transplantation after different periods of organ cold preservation ischemia as well as the effect of superoxide dismutase (SOD) on these changes. For this purpose, male Lewis rats were classified as follows: Group I, Control; Group II, syngenic pancreas transplantation after 15 min of organ preservation in Collins solution at 4 degrees C; Group III, same as II but with 12 hours of organ preservation; Group IV, same as III, but with SOD pretreatment. Results have shown significant posttransplantation increases of both tissue 6-keto PGF1 alpha and urinary 2, 3 dinor 6-keto PGF1 alpha, the latter being a useful marker to evaluate systemic prostacyclin (PGI2) production by rat pancreas. This effect was prevented when the organ had been exposed to SOD during the period of cold preservation ischemia. These results confirm the implication of oxygen-free radicals (OFR) in the ischemia-reperfusion process associated to rat pancreas transplantation leading to enhanced arachidonic acid metabolism.

Lack of specific saxitoxin binding to rat mast cells.

We studied whether or not mast cells are endowed with specific sodium channels, by using tritiated saxitoxin which binds to site 1 of sodium channels on excitable tissues. Our results suggest that rat pleural and peritoneal mast cells lack specific sodium channels.

Changes in rat mast cell responses in sodium-free media. Lack of demonstrable sodium channel activity.

Exposure of rat mast cells to isotonic sucrose (employed as a sodium free medium) increased several-fold the sensitivity to calcium, which itself became a stimulus for exocytosis. Concentrations of the cation as low as 25 microM permitted maximal histamine release. Preincubation of cells in sucrose to allow sodium efflux before adding the ionophore A23187 led to a slower release of histamine. We postulate that sodium efflux can generate a membrane potential that causes the increased sensitivity to calcium and the delay in response after preincubation. The response to A23187 is somewhat unspecific since the ionophore can release histamine from internal calcium reservoirs. Saxitoxin or veratridine did not affect cell responses, so that sodium activity is not mediated through defined sodium channels.