Cell Line-Dependent Adhesion and Inhibition of Proliferation on Carbon-Based Nanofilms

Introduction

Disorganisation of the extracellular matrix (ECM) is strongly connected to tumor progression. Even small-scale changes can significantly influence the adhesion and proliferation of cancer cells. Therefore, the use of biocompatible nanomaterials capable of supporting and partially replenishing degraded ECM might be essential to recover the niche after tumor resection. The objective of this study was to evaluate the influence of graphene, graphene oxide, fullerene, and diamond nanofilms on breast cancer and glioblastoma grade IV cell lines.

Methods

Nanomaterials were characterized using SEM and TEM techniques; zeta potential analysis was also performed. Nanofilms of graphene, fullerene, and diamond nanoparticles were also characterized using AFM. The toxicity was tested on breast cancer MDA.MB.231 and glioblastoma grade IV U-87 MG cell lines, using LDH assay and by counting stained dead cells in bioprinted 3D models. The following parameters were analyzed: proliferation, adhesion to the nanofilm, and adhesion to particular ECM components covered with diamond nanoparticles.

Results and Discussion

Our studies demonstrated that nanofilms of graphene and diamond nanoparticles are characterized by cell-specific toxicity. Those nanomaterials were non-toxic to MDA.MB.231 cells. After applying bioprinted 3D models, diamond nanoparticles were not toxic for both cell lines. Nanofilms made of diamond nanoparticles and graphene inhibit the proliferation of MDA.MB.231 cells after 48 and 72 hours. Increased adhesion on nanofilm made of diamond nanoparticles was only observed for MDA.MB.231 cells after 30 and 60 minutes from seeding the cells. However, analysis of adhesion to certain ECM components coated with diamond nanoparticles revealed enhanced adhesion to tenascin and vitronectin for both tested cell lines.

Conclusion

Our studies show that nanofilm made of diamond nanoparticles is a non-toxic and pro-adhesive nanomaterial that might stabilize and partially replenish the niche after breast tumor resection as it enhances the adhesion of breast cancer cells and inhibits their proliferation.

Simple Blood Test Indicating Sepsis Relapse: A Case Report

Delays in the diagnosis and management of sepsis are associated with higher mortality. Moreover, routine blood tests performed just before hospital discharge are still insufficient for sepsis survivors. In this report, for the first time, dramatic hematological changes found in the blood of a sepsis survivor are described. The pictorial information from microscope images associated with an appropriate set of multiparameter laboratory test results enabled for prediction of sepsis relapse four days before its clinical recognition. Thus, the role of this case report is to encourage medical practitioners to introduce (or re-introduce) blood smears as the helpful adjunctive extension of routine blood testing, especially when sepsis is suspected.

Dependence of diamond nanoparticle cytotoxicity on physicochemical parameters: comparative studies of glioblastoma, breast cancer, and hepatocellular carcinoma cell lines

Reports on the cytotoxicity of diamond nanoparticles (ND) are ambiguous and depend on the physicochemical properties of the material and the tested cell lines. Thus, the aim of this research was to evaluate the influence of thirteen types of diamond nanoparticles, differing in production method, size, and surface functional groups, on their cytotoxicity against four tumor cell lines (T98G, U-118 MG, MCF-7, and Hep G2) and one non-tumor cell line (HFF-1). In order to understand the dependence of diamond nanoparticles on physicochemical properties, the following parameters were analyzed: viability, cell membrane damage, morphology, and the level of intracellular general ROS and mitochondrial superoxide. The performed analyses revealed that all diamond nanoparticles showed no toxicity to MCF-7, Hep G2, and HFF-1 cells. In contrast, the same nanomaterials were moderately toxic for the glioblastoma T98G and U-118 MG cell lines. In general, the effect of the production method did not influence ND toxicity. Some changes in cell response after treatment with modified nanomaterials were observed, with the presence of carboxyl groups having a more detrimental effect than the presence of other functional groups. Although nanoparticles of different sizes caused similar toxicity, nanomaterials with bigger particles caused a more pronounced effect.

Differences in the Cell Type-Specific Toxicity of Diamond Nanoparticles to Endothelial Cells Depending on the Exposure of the Cells to Nanoparticles

Introduction

Diamond nanoparticles are considered to be one of the most cytocompatible carbon nanomaterials; however, their toxicity varies significantly depending on the analysed cell types. The aim was to investigate the specific sensitivity of endothelial cells to diamond nanoparticles dependent on exposure to nanoparticles.

Methods

Diamond nanoparticles were characterized with Raman spectroscopy, Fourier-transform infrared spectroscopy (FTIR) and dynamic light scattering (DLS). Toxicity of diamond nanoparticles was assessed for endothelial cells (HUVEC), human mammary epithelial cells (HMEC) and HS-5 cell line. The effect of diamond nanoparticles on the level of ROS, NO, NADPH and protein synthesis of angiogenesis-related proteins of endothelial cells was evaluated.

Results and Discussion

Our studies demonstrated severe cell type-specific toxicity of diamond nanoparticles to endothelial cells (HUVEC) depending on nanoparticle surface interaction with cells. Furthermore, we have assessed the effect on cytotoxicity of the bioconjugation of nanoparticles with a peptide containing the RGD motive and a serum protein corona. Our study suggests that the mechanical interaction of diamond nanoparticles with the endothelial cell membranes and the endocytosis of nanoparticles lead to the depletion of NADPH, resulting in an intensive synthesis of ROS and a decrease in the availability of NO. This leads to severe endothelial toxicity and a change in the protein profile, with changes in major angiogenesis-related proteins, including VEGF, bFGF, ANPT2/TIE-2, and MMP, and the production of stress-related proteins, such as IL-6 and IL-8.

Conclusion

We confirmed the presence of a relationship between the toxicity of diamond nanoparticles and the level of cell exposure to nanoparticles and the nanoparticle surface. The results of the study give new insights into the conditioned toxicity of nanomaterials and their use in biomedical applications.

Effect of Melittin Complexes with Graphene and Graphene Oxide on Triple-Negative Breast Cancer Tumors Grown on Chicken Embryo Chorioallantoic Membrane

One of the components of bee venom is melittin (M), which has strong lysing properties on membranes. M has high toxicity to cancer cells, but it also affects healthy cells, making it necessary to use methods for targeted delivery to ensure treatment. This research is a continuation of previous studies using graphene nanomaterials as M carriers to breast cancer cells. The studies described below are conducted on a more organized biological structure than what is found in vitro cells, namely, cancerous tumors grown on a chicken embryo chorioallantoic membrane. Caspase 3 and 8 levels are analyzed, and the level of oxidative stress markers and changes in protein expression for cytokines are examined. The results show that M complexes with nanomaterials reduce the level of oxidative stress more than M alone does, but the use of graphene (GN) as a carrier increases the level of DNA damage to a greater extent than the increase caused by M alone. An analysis of cytokine levels shows that the use of the M and GN complex increases the level of proteins responsible for inhibiting tumor progression to a greater extent than the increase occasioned by a complex with graphene oxide (GO). The results suggest that the use of GN as an M carrier may increase the toxic effect of M on structures located inside a cell.

Advances in Management of Fournier's Gangrene by Coupling Intensive Hospital Treatment With Innovative Post-discharge Hyperbaric Oxygen Therapy Rehabilitation: A Case Report

Fournier's gangrene (FG) is a rare form of necrotizing soft tissue infection characterized by an acute, aggressive, and rapidly progressive course. In this case report, we describe advanced therapy combining critical care, surgery, pharmacotherapy, extended biochemical/cellular blood diagnostics, and post-discharge hyperbaric oxygen therapy rehabilitation. Such an intervention resulted in survival and improved health status and quality of life of the patient with FG and septic shock.

Biomechanical changes in the liver tissue induced by a mouse model of multiple sclerosis (EAE) and the effect of anti-VLA-4 mAb treatment

Experimental autoimmune encephalomyelitis (EAE) is a mouse model of demyelinating diseases, such as multiple sclerosis (MS). MS can be accompanied by autoimmune hepatitis. In this study, nanomechanical, biorheological and histological examinations were carried out by atomic force microscopy (AFM), rheology, and immunofluorescence microscopy to investigate changes in the liver tissue of EAE mice and the effect of natalizumab, a monoclonal antibody against α4-integrin (VLA-4) cell adhesion molecule, used in MS therapy. Liver samples collected from EAE mice in three successive phases of the disease showed inflammatory changes manifested by leukocyte infiltrations and elevated levels of proinflammatory cytokine IL-1β. Liver stiffness and viscoelasticity increased in the onset phase of EAE, decreased in the peak phase and increased again in the chronic phase to reach the highest values. These changes were not associated with inflammation parameters which increased in the peak phase and decreased to the lowest values in the chronic phase. Moreover, anti-VLA treatment, which reduced the inflammation parameters, had an ambiguous effect on stiffness and viscoelasticity: it increased them in the peak phase but decreased in the chronic phase. The observed discrepancies can result from a complex network of interactions between inflammation and fibrosis, as well as between liver cells and the extracellular matrix influencing the biomechanical properties of the liver tissue.

Graphene Oxide Scaffold Stimulates Differentiation and Proangiogenic Activities of Myogenic Progenitor Cells

The physiological process of muscle regeneration is quite limited due to low satellite cell quantity and also the inability to regenerate and reconstruct niche tissue. The purpose of the study was to examine whether a graphene oxide scaffold is able to stimulate myogenic progenitor cell proliferation and the endocrine functions of differentiating cells, and therefore, their active participation in the construction of muscle tissue. Studies were carried out using mesenchymal cells taken from 6-day-old chicken embryos and human umbilical vein endothelial cells (HUVEC) were used to assess angiogenesis. The graphene scaffold was readily colonized by myogenic progenitor cells and the cells dissected from heart, brain, eye, and blood vessels did not avoid the scaffold. The scaffold strongly induced myogenic progenitor cell signaling pathways and simultaneously activated proangiogenic signaling pathways via exocrine vascular endothelial growth factor (VEGF) secretion. The present study revealed that the graphene oxide (GO) scaffold initiates the processes of muscle cell differentiation due to mechanical interaction with myogenic progenitor cell.

Exploration of Different Rehabilitation Routes for Sepsis Survivors with Monitoring of Health Status and Quality of Life: RehaSep Trial Protocol

Introduction

This project addresses the important problem of sepsis sequelae resulting in frequent hospital readmissions and higher mortality rate in the post-discharge period. However, neither specific diagnostic methods nor standards for rehabilitation of sepsis patients have been introduced yet. The aim of this study is to evaluate the effectiveness of two different multiparameter-monitored rehabilitation treatments in order to improve the health status and quality of life of sepsis survivors.

Methods

Decades of failed randomized controlled trials involving sepsis patients strongly suggest the need for a paradigm change. Therefore, we designed a prospective, interventional, controlled, pragmatic, patient-centred trial based on the principles of personalized medicine. Sixty post-sepsis patients after hospital discharge will be individually assigned to a control group (without intervention) and two groups with 3-month diagnostically monitored rehabilitation programs based either on the recumbent cycloergometer training or on the experimental hyperbaric oxygen therapy. In all of the patients a wide range of physiological (spirometry, ECG/cycloergometer exercise test), haematological (microscopy) and biochemical (blood tests) parameters will be assessed at hospital discharge and during subsequent 3 months in order to monitor changes of their physical capacity, immunity and degree of post-sepsis organ damage/recovery. For quality of life monitoring a novel tool—“Life After Sepsis Survey”—will be applied.

Planned Outcomes

A set of composite quantitative indices resulting from laboratory measurement data combined with the quality of life questionnaire data will constitute the primary outcomes whereas mortality rate and hospital readmission number will be counted as the secondary outcomes.

Conclusions

Critical analysis of past trials prompted us to implement multiple improvements in tools and procedures. The results of this trial will contribute to the development of rehabilitation therapy addressing not only weakness but also organ damage problems of sepsis survivors.

Trial Registration

ANZCTR (http://www.anzctr.org.au): ACTRN12618000347268, U1111-1210-6110.

Funding

This research was funded by the National Science Center, Poland.

[Does inguinal hernia repair influence on quality of life of elderly males?]

INTRODUCTION

Inguinal hernia repair is a common surgical intervention in elderly which can affect quality of life in the future of these patients. Aim of the study is to assess the quality of life of elderly males after inguinal hernia repair compared with a similar group of male patients without any operation.

MATERIAL AND METHODS

A group of 40 male patients between the age of 60-80, in time up to 2 years after Lichtenstein hernia repair was compared with the same age 50 healthy males not operated in previous 2 years by 2 questionnaires: international Gastrointestinal Quality of Life Index (GQLI) and national Gerontologic Society Investigation Questionnaire to assess possible differences in their quality of life. Both groups were comparable and operation techniques were identical.

RESULTS

Hernia repair resulted in 12 complications (30%): wound infections - 3, serous exudate - 1, chronic pains - 2, inflammatory infiltration - 4, loose sutures - 2. Overall GQLI score in hernia operation group reached mean 123.5 +/- 10.3 and in control group was 121.2 +/- 8.7 (p > 0.37). Gerontologic Society Investigation Questionnaire did not reveal any significant differences between both groups, however it presented rather sad existence of elderly men in our country, who being pensioners are self-limiting their activity on all fields. However, the profile of the hernia group seemed to comprise of people, who keep better physical activity, thus are motivated to be operated for inguinal hernia to keep them in a good physical shape. Some limitations of their postoperative activity were noted, probably because of medical advice or in fear of recurrence of hernia.

CONCLUSIONS

Elderly patients operated for inguinal hernia have similar long term quality of life as a healthy population of the same age. Medical prescription to restrict the physical activity after hernia repair with a mesh should be limited to short necessary time especially in elderly. Further investigations are needed to elaborate methods of increasing activity of old men in Poland to moderate medical costs for this group.

[Characteristics of Lactobacillus strains contained in pharmaceuticals]

The aim of the study was to characterize lactic acid bacteria (LAB) which are components of drugs administered orally in cases of intestinal disturbances, or antibiotic--related diarrhea. Biochemical properties, growth behavior, bile tolerance, and survival at low pH of six LAB strains (four strains L. rhamnosus and two L. acidophilus) were studied. The survival at low pH was determined in MRS broth (Difco) acidified to pH 1; 2; 3; and 4. Bile tolerance was tested on MRS broth with 0.3% oxgall (Difco). Between tested strains differences in ability to grow at low pH and survival in bile were observed. Only 0.01% inoculum of all examined strains survived at pH 1. Differences between strains in survival at low pH (pH 2 and pH 3) and tolerance of bile were observed. However, after 2 h incubation at pH 4, 100% of strains stayed alive. Examined strains demonstrated good 3% bile tolerance. All strains met the criteria for probiotic strains: ability to survive at pH 3 and in the presence of bile.

[Intertrochanteric fractures of the hip treated with dynamic hip screws (DHS)]

The history and concept of sliding fixation is presented. Treatment results of 72 cases with 76 intertrochanteric fractures treated with DHS were analysed. Fractures were classified according to the Kyle scale into 4 different types. 61 males and 11 women age ranging from 46 to 72 years (average age: 65 years) were treated surgically. In 48 cases good results were achieved, in 22 cases results were satisfactory and in 6 cases results were poor. The use of DHS screws is an effective way of treating intertrochanteric fractures among patients with osteoporosis, as well as young patients requiring anatomic reduction of bone fragments. This technique allows early mobilization and weight bearing.

Our experiences in total condylar knee replacement

The purpose of this study was to evaluate the outcomes of total knee replacement using endoprostheses. The material consisted of 78 knee endoprostheses in 68 patients operated in our Clinic over a 3-and-a-half-year period beginning in March 1995. Outcome assessment was based on clinical and radiological examinations before and after surgery, with due regard for the patient's subjective evaluation. The average follow-up period was 13 months. The majority of the patients were found to have improved walk efficiency, eliminated or reduced pain, improved mobility, corrected limb axis, and excellent subjective evaluation.

The application of screws covered with a layer of nanocrystaline diamond in tibia fractures treated with a Polfix fixator: further observations

This article presents further results in the treatment of tibial shaft fractures using a Polfix fixator with screws covered with a layer of nanocrystaline diamond. The advantages of this new protective layer are presented in 16 additional patients. Research to date indicates that nanocrystaline diamond can be used successfully to cover the surface of surgical screws and plates.

Effect of streptozotocin diabetes on fatty acid content and composition of the heart lipids in the rat

The aim of the present study was to examine the effect of diabetes on long chain fatty acid content and composition in the heart lipids. The experiments were carried out on male Wistar rats. Diabetes was induced by intravenous administration of streptozotocin. Samples of the blood and the left ventricle were taken. Lipids were extracted and separated into different fractions. The following fractions were examined: free fatty acids, diacylglycerols, triacylglycerols and phospholipids. The fatty acids from each fraction were identified and quantified by means of gas-liquid chromatography. It was found that diabetes resulted in an almost four-fold elevation in the content of the free fatty acid fraction in the heart, whereas the plasma concentration of free fatty acids increased only two-fold. The diabetes induced changes in the content of particular acids in the fraction of free fatty acid in the heart did not reflect changes in their concentration in the plasma. The content of total di- and triacylglycerol fatty acids also markedly increased in diabetes. In both the compounds, the elevation in the content of individual acids, with the exception of myristic and palmitoleic acid reflected roughly the elevation in their concentration in the plasma. There were, however, several differences in the percentage composition of fatty acids between the two groups. In the fraction of phospholipids, the content of myristic, palmitic, stearic and linoleic acids remained stable, whilst the content of palmitoleic acid was reduced and the content of arachidonic acid was elevated. It is concluded that insulin deficiency results in marked changes in the endogenous lipid fatty acid content of the heart. These changes are not directly related to alterations in the supply of individual acids through the plasma.

[Ender nails in the stabilization of trochanteric fractures of the femur in the elderly]

Results of treatment for trochanteric fracture of the femur in 50 patients aged 25-91 (mean 71 years) are presented. In all cases reviewed the fracture has been stabilized with 3 or 4 Ender nails. In majority of cases bony union has been achieved. Short operating time, small incision remote from fracture site, early weight bearing constitute unquestionable advantages of the method. Most frequent complications as shortening of the extremity involved, excessive external rotation, pain related to migration of the nails, varus deformity at the fracture site were usually found in patients with marked osteoporotic changes.

[Arthroscopic treatment for synovial chondromatosis of the shoulder--case report]

A case of 15 years old schoolgirl with synovial chondromatosis of the right shoulder is presented. The diagnosis has been confirmed by MRI. At arthroscopy approximately 70 oval loose bodies 5-8 mm in size have been removed. Postoperatively, no complication occurred. The case presented demonstrates advantage of arthroscopic treatment of this rare condition.

[Results of treating forearm bone shaft fractures with a 3.5 mm self compressive plate]

Results of 29 forearm bones shaft fracture treatment with 3.5mm self compressive plate in 26 patients aged 18-64 (mean 33) are presented. Open reduction with 3.5mm self compressive plate fixation has been performed in all cases. Anderson et al criteria were used to assess functional and radiological outcome. Excellent and good functional results were achieved in 25 cases, one was rated fair, no poor results were observed.

[Evaluation of the prevalence of osteoporosis in a population of women living in Krakow based on densitometric measurements of the forearm]

Osteoporosis is considered a civilization disease, affecting populations living in big cities. It is detected in 10 percent of population and in 30 percent women over fifty. We tried to estimate prevalence of osteoporosis in people living in Kraków. For estimation purposes, 1000 people living in Kraków more than 40 years were chosen. 325 persons came to our Department for examination, 232 of which were women. All patient filled a special questionnaire on pathological changes in skeletal system and risk factor of osteoporosis. Densitometric measurements of nondominant forearm using Osteometer DTX 100 were performed in all patients. For osteoporosis criteria level of T-score less than -2.5 was taken. Because of lack of Polish reference data for densitometric measurements our data were compared to WHO data, concerning prevalence of osteoporosis in white women. Compared to WHO data, a higher frequency of osteoporosis was found in women living in Kraków more than 40 years.

[Mikrozespol fixator in treatment of metacarpal malunion (preliminary report)]

Results of surgical treatment in 6 patients aged 21-40 (mean 30 years) with metacarpal malunion are presented. External version of Mikrozespol fixator has been used for stabilization of the fragments. Excellent radiographic result has been achieved in all cases. Functional assessment revealed 5 excellent and 1 good result. Bony union occurred after 7 weeks; complete function returned 5 weeks after surgery. The authors conclude, that Mikrozespol stabilization constitutes an alternative method for carpal malunion treatment.

Effect of various types of exercise training on 5'-nucleotidase and adenosine deaminase activities in rat heart: influence of a single bout of endurance exercise

The aim of the present study was to find out whether activities of the enzymes controlling adenosine metabolism, 5'-nucleotidase (5NT) and adenosine deaminase (ADA), in the left ventricle of the rat's heart change after 6 weeks of endurance or sprint training. Additionally, an influence of a single bout of endurance exercise till exhaustion on activities of these enzymes was investigated in sedentary and trained rats. The rats were divided into three groups: (1) sedentary controls (C), (2) endurance-trained (ET), and (3) sprint-trained (ST). It was shown that both types of training increased 5NT, but did not change ADA activity in the rat heart. Acute exercise till exhaustion did not affect 5NT activity in the heart taken from C and ST rats, but decreased its activity in the ET group. The heart ADA activity after exhaustive exercise increased in C and in ET group, but decreased in ST animals. It is concluded that physical training affects cardiac adenosine metabolism and the type of training may exert an influence on purine nucleotides metabolism in the heart during exhaustive exercise.

[Reproducibility of densitometric examinations of the tibial shaft]

The aim of this paper is to evaluate the reproducibility of tibial shaft densitometry in own method under development. It will be expressed as percentage value of coefficient of variability (%CV). Bone mineral content (BMC) and bone mineral density (BMD) were measured with a dual energy X-ray densitometer Lunar DPX; the data were analyzed with a "Orthopedic" software. Three tibial bone scans were done in 10 males. High reproducibility was found, ranging from 0.98% to 1.45% and from 1.45% to 2.08% for BMC and BMD respectively. Reproducibility increases as the analyzed surface increases. Reproducibility so high allows for further investigations; it might be interesting to monitor BMC and BMD of the tibia in course of fracture treatment by Polfix or Zespol method.

[Fixation of neck-head with a single cannulated screw for slipped capital femoral epiphysis--preliminary report]

Results of surgical treatment in 7 patients with slipped capital femoral epiphysis have been presented. Slip angle ranged from 12(to 42(. Closed, in situ neck-head fixation with a single cannulated screw was performed. The screw was introduced percutaneously, through the anterior surface of the femoral neck into the center of the head and perpendicularly to its base. The method employed rendered very good results. No head or neck perforation occurred. No progression of the slip was observed. Soft tissue trauma was only minimal; mobilization was commenced the first postoperative day.

5'-Nucleotidase and adenosine deaminase activities in hypertrophied rat heart. The effect of tachycardia

Activity of 5'-nucleotidase (5NT) and adenosine deaminase (ADA) in the left heart ventricle was examined at normal heart rate and after atrial pacing in six weeks after constriction of the aorta above or below the renal vessels and in sham operated rats. The aorta constriction above the vessels reduced activity of 5NT by 29% and increased activity of ADA by 33%, whereas the constriction below the vessels resulted in elevated activity of both enzymes: 5NT by 16% and ADA by 145% at normal heart rate. The atrial pacing reduced 5NT activity and did not affect ADA activity in control rats and in those with constriction of the aorta below the vessels. The activity of both enzymes increased after constriction of the aorta above the renal vessels. It is concluded that adenosine metabolism in the hypertrophied heart may be changed due to changes in its production and degradation. Renin-angiotensin-aldosterone system seems to be involved in regulation of the activities of adenosine metabolizing enzymes in the hypertrophied heart.

[A trial of ultrasonographic use for evaluating leg lengthening]

Modified de Bastiani method of callotasis with Wagner apparatus was used as a lengthening procedure of 4 femurs and 1 tibia. The ultrasonography was applied to measure the degree of distraction, to determine the eventual axial deviation of the bone ends and to follow up the callus formation in the gap. The obtained results were compared with radiography.

Effects of forskolin on the longitudinal internal resistance (ri) in rabbit sinus node strips

The effect of several concentrations of 7-0-hemisuccinyl, 7-deacetyl forskolin on ri was studied by means of microelectrode and single sucrose gap techniques. Twenty mumol.l-1 of forskolin added to the sucrose gap lowered ri by 15% below the control value. The drug applied at 50 mumol.l-1 initially decreased ri by 31%, and then it increased the resistance by 43% above the control value. The possible mechanisms underlying these effects are discussed in terms of cAMP and Ca action on the cell coupling.

Use of fibrin glue in sucrose gap method

Isolated frog nerves or rabbit sinus node strips were mounted in a single sucrose gap chamber. A fibrin glue Tissucol was used in this arrangement as an intercompartment seal. Under such conditions, the specimens produced stable trans-gap action potentials of relatively high amplitude. In other experiments the gap was filled with fibrin in place of sucrose solution. The results obtained in the fibrin gap experiments resembled these mentioned above.

Effects of cyclic nucleotides on the longitudinal internal resistance in the rabbit sinus node

The effect of dibutyryl cyclic AMP as well as dibutyryl cyclic GMP on the longitudinal internal resistance was studied in the rabbit sinus node strips by means of microelectrode and sucrose gap techniques. Dibutyryl cyclic AMP added to the sucrose gap decreased the resistance and increased the spontaneous rate whereas dibutyryl cyclic GMP evoked the opposite effects. These results suggest that cyclic nucleotides influence the cell coupling in the sinus node.

A method of measurement of longitudinal resistances in an isolated cardiac and smooth muscle preparation

The longitudinal internal as well as external resistance was measured by means of simultaneous intracellular and sucrose gap voltage recordings. The longitudinal internal resistance could be calculated from a formula comprising the shunt resistance, membrane action potential and transgap action potential before and after shunting. The longitudinal external resistance was calculated from another formula comprising the same quantities.