Effect Of Nystatin Research Articles

Effect of Nystatin with and without DMAHDM on Antifungal and Mechanical Properties of Acrylic Resins.

To investigate antifungal and mechanical properties after the impregnation of Dimethyl Amino-ethyl Hexa-decyl Di-methacrylate (DMAHDM) alone or in combination with Nystatin in polymethylmethacrylate. The control group was fabricated by mixing powder and liquid of PMMA at the ratio of 2.5:1 g/mL. The DMAHDM was added to PMMA liquid and were mixed with PMMA powder. The Nystatin (500,000 International Units (IU)) was mixed with PMMA powder, whereby the composite powder was mixed with the DMAHDM-based liquid. The prepared specimens were tested for fungal adhesion testing (at days 1 and 30), impact strength and flexural strength. Oneway ANOVA post-hoc Tukey's test were used for statistical analysis. Statistical analysis for the adhesion assay revealed that the antifungal activities of unaged and aged specimens in experimental groups were statistically significant as compared to control group A. The groups containing DMAHDM with Nystatin have shown statistically reduced flexural strength. The impact strength test revealed that groups containing 20% DMAHDM alone and DMAHDM with Nystatin showed statistically reduced impact strength compared to the control group. Antifungal activities of experimental PMMA resin was increased. The addition of DMAHDM alone in PMMA resin has no deleterious effects on impact and flexural strength, however, at higher concentration values were reduced.

Inhibitory Effect of Nepeta Crispa L. and Nepeta Cataria Extracts on Candida Albicans Growth: An In-vitro Study

Background and Objectives Considering the existence of many medicinal plants in Iran and the high prevalence of oral candidiasis, the present study aims to evaluate the inhibitory effects of Nepeta crispa L. and Nepeta cataria extracts on Candida albicans growth. Subjects and Methods After preparing the extracts of two plants, their minimum inhibitory concentration (MIC) and minimum lethal concentration (MLC) for C albicans were measured by broth microdilution method. The inhibitory effect of the extracts was evaluated by the disk diffusion method and measuring the diameter of inhibition zone. Data were analyzed in SPSS software, version 22. The significant level was set at 0.05. Results The MIC of N. crispa L. and N. cataria extracts was 1.1 and 2.4 μg/mL, respectively. Their MLC was 4 and 6 μg/mL, respectively. The highest inhibition zone diameter was for nystatin (21.31 mm), while the lowest diameter was for N. cataria extract (11.60 mm). No. significant difference was observed in the inhibition zone diameter between nystatin and N. crispa L. extract (P>0.05). Conclusion The inhibitory effect of N. crispa L. extract on the candida albicans growth is not significantly different from the effect of nystatin. Although N. cataria extract has inhibitory effect, its effect is significantly lower than the effect of nystatin.

In Vitro Effects of Propolis Mouthwash and Nystatin on Candida Albicans: A Comparative Study

Background & Objective: Oral candidiasis is the most common fungal infection of the oral cavity, mainly caused by the overgrowth of Candida albicans. One of the topical medications for candidiasis is nystatin, a polyene antifungal agent. Nevertheless, increased resistance to this drug because of overprescription has caused recurrent oral candidiasis. There is a lot of interest today in the use of natural products and compounds due to the side effects of synthetic products. Propolis is a natural resin substance produced by bees through the combination of wax and saliva with resins collected from plants, which has reportedly antibacterial, antifungal and antitumor properties. The purpose of this study was to compare the effects of propolis mouthwash and nystatin on C. albicans. Materials & Methods: The present in vitro study, in which the effects of antifungal agents were investigated on the standard strain of C. albicans, was conducted within two groups of 15, nystatin and propolis, using the Kirby-Bauer disc diffusion susceptibility test after preparation and sterilization. The diameter of the zone of inhibition (ZOI) was measured in this assay using the disc diffusion method onto Sabouraud dextrose agar (SDA) medium. Results: Statistical analysis of data by SPSS software using t-test statistics to evaluate the antifungal effect of the interventions showed a better antifungal effect of nystatin compared to propolis mouthwash against C. albicans (P<0.001). Conclusion: The findings of this study demonstrated that the local propolis mouthwash was less potent than nystatin in inhibiting the growth of C. albicans, probably due to differences in the concentration and geographical region of collected propolis. Further research on species isolated from oral biofilm is needed to achieve complementary outcomes.

Analysis of the Effect of Nystatin Combined with Lactobacillus on Mycotic Vaginitis

Analysis of the Effect of Nystatin Combined with Lactobacillus on Mycotic Vaginitis

An In Vitro Analysis of the Antifungal Effect of Nystatin and Fluconazole Incorporated into Tissue Conditioner with and Without Using Varnish Containing Self-cured Resin and 1,1,1-Trichloroethane

Background: Incorporating antifungal drugs into liners has been proposed to treat denture stomatitis. Varnish application on tissue conditioners can decrease the porosities and irregularities, biofilm, and pathogens adhesion. In this study, we evaluated the effect of varnish application on releasing the antifungal drugs incorporated into tissue conditioners. Methods: Pure form of nystatin and fluconazole were mixed into tissue conditioner powder separately at 5% wt/wt concentration and prepared according to manufacturer’s instruction. Then, disk-shaped specimens (5 mm in diameter and 1 mm in thickness) were prepared at 30 nystatin and 30 fluconazole specimens. Varnish (containing 50 mL of 1,1,1-trichloroethane and 3 ml of self-cured resin) was applied on the surface of 15 disks of each drug and the other specimens were used as the control group (without varnish). Next, the disks were put in agar plates cultured with standard Candida albicans and incubated for 7 days. Mean inhibition diameter for each disk was measured with digital caliper at 24 hours, 3 days, and 7 days. Each step was performed in triplicate. Data was analyzed with one-way ANOVA and Friedman, Wilcoxon, and Mann-Whitney U tests. Results: The mean inhibition diameter (MID) at days 1, 3, and 7 in fluconazole without varnish group was 12.63, 3.90, and 3.67, respectively; in fluconazole with varnish was 3.00, 2.50, and 2.50, respectively; in nystatin without varnish was 5.78, 3.90, and 3.87, respectively; in nystatin with varnish group was 2.50, 0.00, and 0.00, respectively. fluconazole without varnish group exhibited significantly higher MID and nystatin with varnish group had lower MID. Conclusions: In this experimental study, fluconazole was more effective than nystatin. In groups without varnish, antifungal effect continued up to day 7. Using varnish in tissue conditioner can decrease antifungal effect.

Antifungal Activity of Ethanol-extracted Bixa orellana (L) (Achiote) on Candida albicans, at Six Different Concentrations

The aim of the study was to determine the antifungal activity of six different concentrations of the ethanol extract of Bixa orellana (L) (Achiote) on the strains of Candida albicans (ATCC 90028). The ethanol extract of Bixa orellana (L) (BEE) was prepared in six different concentrations (5%, 10%, 20%, 40%, 60%, and 100%), which were confronted with the positive control group (Nystatin 100,000 UI/mL). The total sample consisted of n = 174 wells inoculated with each concentration evaluated in the Petri dishes. The cultivation procedure was carried out at a temperature of 37°C, and then the 6 mm diameter wells on which the sowing of the Candida albicans in suspension was carried out. Subsequently, the BEE (Achiote) was inoculated in all the concentrations mentioned in the same way for Nystatin; finally, the inhibition halos were evaluated by the Kirby-Bauer method at the scheduled times of 24, 48, and 72 hours. The highest antifungal activity was found at 24 hours and this increased directly proportional to the concentration of BEE (5%, 10%, 20%, 40%, 60%, and 100%): 11 ± 0, 11 ± 0, 13.1 ± 1.3, 17.2 ± 0.8, 19.1 ± 1.0, and 21.4 ± 1.3 mm, respectively. However, there was no statistically significant difference when compared with Nystatin, at p > 0.05 Conclusion: It was shown that 5%, 10%, 20%, 40%, 60%, and 100% BEE had an antifungal effect against Candida albicans. However, there were no statistically significant differences against the effect of Nystatin at 100,000 IU/mL, who has an inhibitory effect greater than BEE, with a significance level of p < 0.05. This article describes the antifungal activity and the possible impact on dentistry that the use of Bixa orellana (L) may have because according to our results it had an antifungal effect against strains of Candida albicans. This opens a great line of research to potentially use this natural resource in dentistry. How to cite this article: Poma-Castillo L, Espinoza-Poma M, Mauricio F, et al. Antifungal Activity of Ethanol-extracted Bixa orellana (L) (Achiote) on Candida albicans, at Six Different Concentrations. J Contemp Dent Pract 2019;20(10):1159-1163.

Nystatin Modulates Genes in Immunity and Wingless Signaling Pathways in Cow Blood

Nystatin is an antifungal agent isolated from bacteria found in the dairy cow environment. It disrupts small platforms in the cell membrane, composed of sphingolipids and cholesterol known as lipid rafts. Pathogen recognition receptors (PRR) may be embedded in these lipid rafts. This study was conducted to evaluate the in vitro effects of the lipid raft inhibitor Nystatin, on the expression of genes in the innate and adaptive immunity and wnt signaling pathway in cow peripheral blood. Blood collected from four adult female Holstein-Friesian cows (n=4) was treated with 100ng/mL of Nystatin in vitro. Samples treated with Phosphate Buffer Saline served as control. Total protein concentration and prostaglandin E2in plasma were determined. Total RNA was isolated from cells and was used for cDNA synthesis. The effect of Nystatin on the expression of 84 genes on the cow Wingless signaling pathway and human innate and adaptive immunity arrays were assessed in cow blood using real-time PCR. Fold change in transcript abundance was calculated using Livak’s method. Nystatin was found to modulate transcription and translation of genes involved in homeostasis and immunity in cow blood. It also increased the concentration of total plasma protein and PGE2in cow blood and may thus have had a pro-inflammatory effect. This study provides evidence for the association between lipid raft inhibition and alterations in the wingless signaling pathway in ruminant blood. Furthermore, the results presented may inform antifungal drug design and use in cows.

Nystatin prophylaxis and treatment in severely immunodepressed patients.

Nystatin is sometimes used prophylactically in patients with severe immunodeficiency or in the treatment of fungal infection in such patients, although its effect seems to be equivocal. To study whether nystatin decreases morbidity and mortality when given prophylactically or therapeutically to patients with severe immunodeficiency. We searched PubMed from 1966 to 7 July 2014 and the reference lists of identified articles. Randomised clinical trials comparing nystatin with placebo, an untreated control group, fluconazole or amphotericin B. Data on mortality, invasive fungal infection and colonisation were independently extracted by both authors. A random-effects model was used unless the P value was greater than 0.10 for the test of heterogeneity. We included 14 trials (1569 patients). The drugs were given prophylactically in 12 trials and as treatment in two. Eleven trials were in acute leukaemia, solid cancer, or bone marrow recipients; one in liver transplant patients; one in critically ill surgical and trauma patients; and one in AIDS patients. Nystatin was compared with placebo in three trials, with fluconazole in 10, and amphotericin B in one; the dose varied from 0.8 MIE to 72 MIE daily and was 2 mg/kg/d in a liposomal formulation. The effect of nystatin was similar to that of placebo on fungal colonisation (relative risk (RR) 0.85, 95% confidence interval (CI) 0.65 to 1.13). There was no statistically significant difference between fluconazole and nystatin on mortality (RR 0.75, 95% CI 0.54 to 1.03) whereas fluconazole was more effective in preventing invasive fungal infection (RR 0.40, 95% CI 0.17 to 0.93) and colonisation (RR 0.50, 95% CI 0.36 to 0.68). There were no proven fungal infections in a small trial that compared amphotericin B with liposomal nystatin. The results were very similar if the three studies that were not performed in cancer patients were excluded. For the 2011 and 2014 updates no additional trials were identified for inclusion. Nystatin cannot be recommended for prophylaxis or the treatment of Candida infections in immunodepressed patients.

Differential regulation of CC chemokine ligand 2 and CXCL8 by antifungal agent nystatin in macrophages

The polyene antifungal antibiotic nystatin can interact with cholesterol, thereby altering the composition of the plasma membrane in eukaryotic cells. We investigated whether nystatin influences responses to the infection by inducing expression of chemokines. THP-1 macrophages rarely expressed CC chemokine ligand 2 (CCL2) and CXCL8. However, nystatin dose-dependently increased CCL2 and CXCL8 expression at the mRNA and protein levels. To understand the molecular mechanisms of the antifungal agent, we identified cellular factors activated by nystatin and those involved in nystatin-induced upregulation of CCL2 and CXCL8. Treatment with nystatin resulted in enhanced phosphorylation of Akt, ERK1/2, p38 MAPK, and JNK. Treatment with cholesterol, LY294002, Akt inhibitor IV, U0126, and SP6001250 resulted in abrogation or significant attenuation of nystatin-induced CCL2 expression. Nystatin-mediated CXCL8 expression was attenuated in the presence of Akt inhibitor IV and SP6001250. These results indicate that exposure of human macrophages to nystatin can lead to differential regulation of CCL2 and CXCL8 via the activation of multiple cellular kinases. We propose that upregulation of CCL2 and CXCL8 contributes to pharmacological effects of nystatin.

Effects and Mechanisms of Action of Polyene Macrolide Antibiotic Nystatin on Babesia gibsoni In Vitro

Nystatin is a membrane-active polyene macrolide antibiotic and a channel-forming ionophore. Nystatin exhibits in vitro activity against Babesia gibsoni infecting normal canine erythrocytes containing low potassium (LK) and high sodium concentrations, i.e., LK erythrocytes. The calculated IC(50) value of nystatin against B. gibsoni infecting LK erythrocytes was 31.96 µg/ml. The anti-babesial activity of nystatin disappeared when B. gibsoni in LK erythrocytes were incubated in culture media containing high potassium concentrations (HK). Moreover, when the parasites were harbored in canine HK erythrocytes, which contained high potassium and low sodium concentrations as a result of high Na-K-ATPase activity, the in vitro anti-babesial activities of nystatin also disappeared, apparently due to protection by HK erythrocytes. This suggested that nystatin could show in vitro anti-babesial activity against B. gibsoni by its ionophorous activity, the same as other ionophores such as valinomycin. Subsequently, the effects of nystatin on the host cells were observed. Nystatin could not modify the intracellular concentrations of potassium, sodium, adenosine triphosphate, or glucose in either LK or HK erythrocytes, although it caused weak hemolysis in HK erythrocytes. In addition, nystatin did not affect the survival of canine peripheral polymorphonuclear leukocytes. In conclusion, nystatin destroyed B. gibsoni by ionophorous activity but did not affect either canine erythrocytes or leukocytes in vitro.

Alpha Particles Induce Apoptosis through the Sphingomyelin Pathway

The sphingomyelin pathway involves the enzymatic cleavage of sphingomyelin to produce ceramide, a second messenger that serves as a key mediator in the rapid apoptotic response to various cell stressors. Low-linear energy transfer (LET) γ radiation can initiate this pathway, independent of DNA damage, via the cell membrane. Whether short-ranged, high-LET α particles, which are of interest as potent environmental carcinogens, radiotherapies and potential components of dirty bombs, can act through this mechanism to signal apoptosis is unknown. Here we show that irradiation of Jurkat cells with α particles emitted by the ²²⁵Ac-DOTA-anti-CD3 IgG antibody construct results in dose-dependent apoptosis. This apoptosis was significantly reduced by pretreating cells with cholesterol-depleting nystatin, a reagent known to inhibit ceramide signaling by interfering with membrane raft coalescence and ceramide-rich platform generation. The effects of nystatin on α-particle-induced apoptosis were related to disruption of the ceramide pathway and not to microdosimetry alterations, because similar results were obtained after external irradiation of the cells with a broad beam of collimated α particles using a planar ²⁴¹Am source. External irradiation allowed for more precise control of the dosimetry and geometry of the irradiation, independent of antibody binding or cell internalization kinetics. Mechanistically consistent with these findings, Jurkat cells rapidly increased membrane concentrations of ceramide after external irradiation with an average of five α-particle traversals per cell. These data indicate that α particles can activate the sphingomyelin pathway to induce apoptosis.

A study of the inhibitory effect of the Ethanolic extract of Cyperus rotundus , Eugenia caryophyllus and Coriandrum sativum on the in vitro growth of Candida albicans on a Sabouraud Dextrose Agar

The present study was designed to evaluate the inhibitory effects of three local plant ethanolic extracts (Cyperus rotundus , Eugenia caryophyllus and Cariandrum sativum ) against the growth of Candida albicans in culture media by using of agar well diffusion method. For this purpose graduate concentrates for each extract ( 25 , 50 , 100 , 150 , 200 , 400 )mg/ml prepared and tested .The result showed that the extract of Cyperus rotundus was more effective than Eugenia caryophyllus ,while Coriandrum sativum has no effect in all concentrates on Candida albicans. The statistical analysis by using ANOVA with LSD at level (p&lt;0.05) showed that the concentrations 200 , 400 mg/ml for Cyperus rotundus and 200 mg/ml for Eugenia caryophyllus were a significantly preeminence on the effect of other concentrations and from the effect of Nystatin and Clotrimazole .

The model of fungal population dynamics affected by nystatin

AbstractFungal diseases are acute problems of the up‐to‐day medicine. Significant increase of resistance of microorganisms to the medically used antibiotics and a lack of new effective drugs follows in a growth of dosage of existing chemicals to solve the problem. Quite often such approach results in side effects on humans. Detailed study of fungi‐antibiotic dynamics can identify new mechanisms and bring new ideas to overcome the microbial resistance with a lower dosage of antibiotics. In this study, the dynamics of the microbial population under antibiotic treatment was investigated. The effects of nystatin on the population of Saccharomyces cerevisiae yeasts were used as a model system. Nystatin effects were investigated both in liquid and solid media by viability tests. Dependence of nystatin action on osmotic gradient was evaluated in NaCl solutions. Influences of glucose and yeast extract were additionally analyzed. A “stepwise” pattern of the cell death caused by nystatin was the most intriguing. This pattern manifested in periodical changes of the stages of cell death against stages of resistance to the antibiotic. The mathematical model was proposed to describe cell‐antibiotic interactions and nystatin viability effects in the liquid medium. The model implies that antibiotic ability to cause a cells death is significantly affected by the intracellular compounds, which came out of cells after their osmotic barriers were damaged © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010

Effects of nystatin, fluconazole and propolis on poly(methyl methacrylate) resin surface

The prevalence of candidosis in denture wearers is as well established as its treatment with antifungal agents (AAs). However, little research has been done regarding the effects of AAs on denture base surfaces. Therefore, the aim of this study was to evaluate the effects of fluconazole (FLU), nystatin (NYS) and propolis orabase gel (PRO) on poly (methyl-methacrylate) (PMMA) surfaces. Deionized water and orabase gel without any active component were used as control groups. Conventional heat-polymerized (Clássico) and microwave-polymerized (Onda Cryl) acrylic resins were used. After polymerization, the specimens were polished and had their surfaces evaluated for roughness, free energy and Knoop hardness. Subsequently, specimens were immersed in AAs and controls for 14 days at 35+/-2 degrees C and all variables were measured again. Data were analyzed statistically by 2-way ANOVA followed by Tukey's test (alpha=0.05). Roughness results showed similar behavior for both PMMA resins, with PRO reaching the highest values and differing significantly from the other AAs (p<0.05). No statistically significant differences (p>0.05) were found between the two PMMA resins or between NYS and FLU as regards surface free energy. In conclusion, PRO was able to induce changes in PMMA surface properties, such as roughness, which could be related to microbial adhesion.

Exploring the Mode-of-Action of Bioactive Compounds by Chemical-Genetic Profiling in Yeast

Discovering target and off-target effects of specific compounds is critical to drug discovery and development. We generated a compendium of "chemical-genetic interaction" profiles by testing the collection of viable yeast haploid deletion mutants for hypersensitivity to 82 compounds and natural product extracts. To cluster compounds with a similar mode-of-action and to reveal insights into the cellular pathways and proteins affected, we applied both a hierarchical clustering and a factorgram method, which allows a gene or compound to be associated with more than one group. In particular, tamoxifen, a breast cancer therapeutic, was found to disrupt calcium homeostasis and phosphatidylserine (PS) was recognized as a target for papuamide B, a cytotoxic lipopeptide with anti-HIV activity. Further, the profile of crude extracts resembled that of its constituent purified natural product, enabling detailed classification of extract activity prior to purification. This compendium should serve as a valuable key for interpreting cellular effects of novel compounds with similar activities.

Nystatin prophylaxis and treatment in severely immunodepressed patients.

Nystatin is sometimes used prophylactically in patients with severe immunodeficiency or in the treatment of fungal infection in such patients, although the effect seems to be equivocal. To study whether nystatin decreases morbidity and mortality when given prophylactically or therapeutically to patients with severe immunodeficiency. MEDLINE and The Cochrane Library using a comprehensive search strategy. Contacted industry and scanned reference lists. Randomised trials comparing nystatin with placebo, an untreated control group, fluconazole or amphotericin B. Data on mortality, invasive fungal infection and colonisation were extracted by both authors independently. The outcomes were weighted by the inverse variance. A random effects model was used unless p>0.10 for the test of heterogeneity. We included 10 trials (1, 122 patients). The drugs were given prophylactically in eight trials and as treatment in two. Six trials were in acute leukaemia, one mainly in cancer, one in liver transplant patients, one in critically ill surgical and trauma patients, and one in AIDS patients. Nystatin had been compared with placebo in three trials and with fluconazole in seven; the dose varied from 1.5 MIE to 72 MIE daily. The effect of nystatin was similar to that of placebo on fungal colonisation (relative risk 0.85, 95% confidence interval 0. 65 to 1.13). There was no difference between fluconazole and nystatin on mortality (relative risk 0.87, 0.52 to 1.44) whereas fluconazole was more effective in preventing invasive fungal infection (relative risk 0.42, 0.16 to 1.12) and colonisation (relative risk 0.50, 0.36 to 0.71). The results were very similar if the three studies which were not performed in cancer patients were excluded. Nystatin cannot be recommended for prophylaxis or treatment of Candida infections in immunodepressed patients.

Effect of nystatin on the release of glycerol from salt-stressed cells of the salt-tolerant yeast Zygosaccharomyces rouxii.

The polyene antibiotic nystatin, which affects fungal membrane permeability, inhibited the growth of Zygosaccharomyces rouxii grown in medium containing 15% (w/v) NaCl, whereas yeast grown in medium without NaCl were only slightly inhibited. Nystatin caused salt-stressed cells to release large amounts of glycerol and inhibited their growth, but amino acids and materials with an absorbance at 260 nm were not released from the cells. The leakage was increased by the addition of glucose, and more than 90% of the intracellular glycerol was released into the medium during a 2-h incubation with 0.11 microM nystatin and 2% (w/v) glucose. Glycerol was indispensable for the growth of Z. rouxii grown in culture medium containing 15% NaCl.

Nystatin Effects on Vacuolar Function inSaccharomyces cerevisiae

The effects of nystatin, a polyene antibiotic, was studied in Saccharomyces cerevisiae by isolating and characterizing nystatin-sensitive mutants. We isolated a number of nystatin-sensitive mutants by ethylmethane sulfonate mutagenesis. One of these mutants, the nss1 mutant, was characterized in detail. The mutant was sensitive to stresses such as high temperature or high concentrations of monovalent and divalent cations. The nss1 mutants showed severe vacuolar protein sorting and vacuolar morphology defects. The nss1 mutant was demonstrated to have a mutational lesion in the known VPS16 gene, which is essential for vacuolar protein sorting in S. cerevisiae. All of the vacuolar deficient mutants (vps11, vps16, vps18, and vps33) were sensitive to nystatin. Nystatin was found to cause extensive enlargement of the vacuole in wild-type S. cerevisiae cells. These results are discussed with special reference to the vacuolar function of S. cerevisiae.

Kinetic evaluation of conidial germination of Botrytis cinerea by a spectrofluorometric method

A fluorometric-based method for the kinetic measurement of conidia growth of Botrytis cinerea in liquid culture is described. The method involves an oxido-reduction dye, Alamar blue, as an indicator of growth. The effect of nystatin a non-specific antifungal agent, was studied on conidial germination. An excellent correlation was found between the IC50 obtained by the fluorometric method, and by microscopic measurement. The method is rapid and quantitative, and requires only a small amount of chemicals and fungal material. Since the measurements were performed in a 96-well plate, it is possible to test many different parameters in parallel.

Anin vitro study of the effect of nystatin on permeases of eukaryotic cells

Use of a 2-dimensional spectrophotometer allows the detection and analysis of spatiotemporal patterns in biological samples the "in vitro" system yeast extract behaves as an excitable medium. Oscillatory degradation of trehalose yields NADH-oscillations which, after running out, convert to spatiotemporal waves the observation of excitability coupled to oscillatory processes in biological systems might provide new insights into the meaning of oscillations for metabolism with an "in vitro" system at hand, it should be possible to perform defined experimental manipulations in order to detect the mechanism for excitability in biological systems.