Left atrial remodeling and voltage-guided ablation outcome in obese patients with persistent atrial fibrillation

Background

Obesity is a risk factor for atrial fibrillation (AF). Data regarding left atrial (LA) remodeling in obese patients are scarce. Whether obesity favors AF recurrence after catheter ablation (CA) is still controversial. We assessed the distribution of epicardial atrial fat on computed tomography (CT), LA bipolar voltage, low-voltage zone (LVZ) extent, and the outcome of voltage-guided ablation of persistent AF in obese and non-obese patients.

Methods

A total of 139 patients with persistent AF undergoing a first voltage-guided ablation were enrolled and divided into two groups: 74 were non-obese and 65 were obese. Epicardial adipose tissue (EAT) was assessed on a CT scanner. LA endocardial voltage maps were obtained using a 3D mapping system in sinus rhythm. LVZ was defined as a bipolar peak-to-peak voltage amplitude <0.5 mV.

Results

LA volume, voltage, and EAT amount were similar in the two groups. LVZ was less frequent in obese patients [12 (18.8%) vs. 26 (35.1%), p = 0.05], particularly on the anterior wall. The posterior and lateral EATs were correlated with posterior and lateral LVZ extent, respectively, in obese patients. After 36 months of follow-up, the AF-free survival rate was similar. Lateral EAT [odds ratio (OR) 1.21, 95% confidence interval (CI) 1-1.4, p = 0.04] and P-wave duration (OR 1.03, 95% CI 1-1.05, p = 0.03), but not body mass index (BMI), were predictors of AF recurrence after CA.

Conclusion

In obese patients, LVZ was less marked than in non-obese patients with similar LA volumes, voltage, and EAT amounts. In obese patients, posterior and lateral EATs were correlated with posterior and lateral LVZ extents. Obese patients had a similar and favorable 36-month outcome after AF ablation. BMI was not predictive of AF recurrence.

Impact of gender on left atrial low-voltage zones in patients with persistent atrial fibrillation: results of a voltage-guided ablation

Background

Gender-related differences have been reported in atrial fibrotic remodeling and prognosis of atrial fibrillation (AF) patients after ablation. We assessed in persistent AF the regional distribution of left atrial (LA) bipolar voltage and the extent of low-voltage zones (LVZ) according to gender as well as the results of a voltage-guided substrate ablation.

Methods

Consecutive patients who underwent a voltage-guided AF ablation were enrolled. LA endocardial voltage maps were obtained using a 3D electro-anatomical mapping system in sinus rhythm. LVZ was defined as <0.5 mV.

Results

A total of 115 patients were enrolled (74 men, 41 women). The LA bipolar voltage amplitude was twice lower in the whole LA (p < 0.01) and in each atrial region in women compared with men, whereas the LA indexed volume was similar. LVZ were found in 56.1% of women and 16.2% of men (p < 0.01). LVZ were also more extensive in women (p = 0.01), especially in the anterior LA. Atrial voltage alteration occurred earlier in women than in men. In a multivariate analysis, the female sex (OR 12.99; 95% CI, 3.23-51.63, p = 0.0001) and LA indexed volume (OR 1.09; 95% CI, 1.04-1.16, p = 0.001) were predictive of LVZ. Atrial arrhythmia-free survival was similar in men and women 36 months after a single ablation procedure.

Conclusion

The study reports a strong relationship between the female gender and atrial substrate remodeling. The female gender was significantly associated with higher incidence, earlier occurrence, and greater extent of LVZ compared with men. Despite the female-specific characteristics in atrial remodeling, LVZ-guided ablation may improve the AF ablation outcome in women.

Subcutaneous Implantable Cardioverter-Defibrillators in Patients With Congenital Heart Disease

BACKGROUND

Very few data have been published on the use of subcutaneous implantable cardioverter-defibrillators (S-ICDs) in patients with congenital heart disease (CHD).

OBJECTIVES

The aim of this study was to analyze outcomes associated with S-ICDs in patients with CHD.

METHODS

This nationwide French cohort including all patients with an S-ICD was initiated in 2020 by the French Institute of Health and Medical Research. Characteristics at implantation and outcomes were analyzed in patients with CHD.

RESULTS

From October 12, 2012, to December 31, 2019, among 4,924 patients receiving an S-ICD implant in 150 centers, 101 (2.1%) had CHD. Tetralogy of Fallot, univentricular heart, and dextro-transposition of the great arteries represented almost one-half of the population. Patients with CHD were significantly younger (age 37.1 ± 15.4 years vs 50.1 ± 14.9 years; P < 0.001), more frequently female (37.6% vs 23.0%; P < 0.001), more likely to receive an S-ICD for secondary prevention (72.3% vs 35.9%; P < 0.001), and less likely to have severe systolic dysfunction of the systemic ventricle (28.1% vs 53.1%; P < 0.001). Over a mean follow-up period of 1.9 years, 16 (15.8%) patients with CHD received at least 1 appropriate shock, with all shocks successfully terminating the ventricular arrhythmia. The crude risk of appropriate S-ICD shock was twice as high in patients with CHD compared with non-CHD patients (annual incidences of 9.0% vs 4.4%; HR: 2.1; 95% CI: 1.3-3.4); however, this association was no longer significant after propensity matching (especially considering S-ICD indication, P = 0.12). The burden of all complications (HR: 1.2; 95% CI: 0.7-2.1; P = 0.4) and inappropriate shocks (HR: 0.9; 95% CI: 0.4-2.0; P = 0.9) was comparable in both groups.

CONCLUSIONS

In this nationwide study, patients with CHD represented 2% of all S-ICD implantations. Our findings emphasize the effectiveness and safety of S-ICD in this particularly high-risk population. (S-ICD French Cohort Study [HONEST]; NCT05302115).

Accessory pathways in monozygotic twins with different clinical phenotypes: a case report

Background

The atrioventricular reentrant tachycardia (AVRT) is the most common tachycardia associated with accessory pathways (APs). Although sporadic Wolff-Parkinson-White (WPW) syndrome has been well-described, AP occurrence in identical twins with WPW syndrome remains rarely reported.

Case presentation

We report a case of 14-year-old monozygotic twin brothers referred for an electrophysiology (EP) study. Twin A presented with recurrent symptomatic narrow complex tachycardia after exercise, noted for 3 years. His 12-lead surface electrocardiogram (ECG) did not show ventricular pre-excitation. However, an orthodromic AVRT utilizing a concealed right posteroseptal AP was found and successfully ablated. AVRT did not recur 12 months after the procedure. Twin B was asymptomatic. During his medical examination for firefighter volunteerism, his 12-lead ECG showed a spontaneous ventricular pre-excitation. EP study revealed a short anterograde right midseptal AP, which was then successfully eliminated by catheter ablation. His 12-lead ECG showed no ventricular pre-excitation recurrence 12 months after the procedure.

Conclusions

These identical twin brothers had a right-side AP in almost the same place but showed completely different phenotypes. This case clearly illustrates the difficulty in understanding genetic contribution in the origin of atrioventricular APs. Environmental exposure could play a role in their clinical presentations and AP electrophysiological properties.

Efficacy and safety of the new TightRail™ mechanical sheath for transvenous lead extraction: Results of a French multicenter study

INTRODUCTION

The aim of this study was to assess the safety and efficacy of the TightRail™ sheath for pacemaker/defibrillator transvenous lead extraction (TLE).

METHODS

Multicenter observational study including patients who underwent a TLE with the TightRail™ sheath in five French university hospitals from September 2014 to January 2020.

RESULTS

Two hundred and twenty-five patients (76% males, 71 ± 12 years) underwent a TLE procedure with the TightRail™. A total of 438 leads were extracted using the TightRail™, and the mean age of the extracted leads was 128 ± 85 months; of these, 344 (79%) were pacing leads and 94 (21%) were implantable cardioverter defibrillator leads. The overall clinical success of the extraction procedures was 93%. Overall, 410 of the 438 leads (95%) were extracted (complete or incomplete removal). After multilevel mixed-effects logistic regression model, we found that lead age (odds ratio [OR], 95% confidence interval [CI] for a 1 year increase: 1.11 [1.07-1.15], p < .001) and number of leads extracted (OR, 95% CI: 2.09 [1.50-2.96], p < .001) were the two independent factors associated with complete lead removal failure. Finally, there were 7 (3%) cases of major complications but no per-procedural death.

CONCLUSION

This is the first large-scale survey assessing the efficacy and safety profile of the Tightrail™ mechanical sheath. The clinical success rate was 93%, and the lead removal failure was dependent on the age and number of leads. We show a satisfactory safety profile in this cohort of patients from primarily low-volume centers with older leads.

Delayed pulmonary embolism after COVID-19 pneumonia: a case report

Background 

Since the onset of the COVID-19 pandemic, several cardiovascular manifestations have been described. Among them, venous thromboembolism (VTE) seems to be one of the most frequent, particularly in intensive care unit patients. We report two cases of COVID-19 patients developing acute pulmonary embolism (PE) after discharge from a first hospitalization for pneumonia of moderate severity.

Case summary 

Two patients with positive RT-PCR test were initially hospitalized for non-severe COVID-19. Both received standard thromboprophylaxis during the index hospitalization and had no strong predisposing risk factors for VTE. Few days after discharge, they were both readmitted for worsening dyspnoea due to PE. One patient was positive for lupus anticoagulant.

Discussion 

Worsening respiratory status in COVID-19 patients must encourage physicians to search for PE since SARS-CoV-2 infection may act as a precipitant risk factor for VTE. Patients may thus require more aggressive and longer thromboprophylaxis after COVID-19 related hospitalization.

Success and complication rate of Tightrail mechanical percutaneous lead extraction: a multicenter French study

Background

Our objective was to assess Philips TightRail™ rotating dilator sheath efficacy and safety for extraction of endocardial leads. No large scale multicenter data is available on this mechanical lead extraction device, now commonly used in France.

Methods and results

We conducted a retrospective, multicenter (from 4 French university hospitals) study. These centers that only perform mechanical lead extraction using this device were selected on the basis of the annual volume of procedures (&gt;10 leads/year). All patients from January 2015 to January 2020 who underwent at least one extraction of an endocardial lead with using TightRail™ were included. All of the extracted leads were &gt;12 months old and indications for extraction were based on ESC guidelines.

Overall, 395 leads were extracted using TightRail™ in 203 patients (mean age 70 years, 75% male sex).

Indications for lead removal included cardiac device infection in 172 (85%) cases, lead malfunction in the 25 (12%) cases, vein thrombosis in 3 (1.5%) cases and 3 for other indications (1,5%). The extracted devices were pacemaker in 134 (66%) cases, implantable cardioverter-defibrillator (ICD) in 69 (44%) cases. The mean time from implantation was 124 months. Complete procedural success with TightRail™ system alone was achieved in 180 (89.1%) patients (352 leads) and overall clinical success was 93% (367 leads). Fifteen right sided leads were completely removed with the help of femoral snare. Ten (5%) patients had at least one major perioperative complication: 3 cardiac tamponades, 1 haemothorax, 1 stroke, 5 vascular breaches requiring surgical intervention. No in-hospital death was observed.

Conclusion

Our large scale retrospective study in 4 high-volume mechanical lead extraction centers shows that TightRail™ is highly effective for chronically implanted lead extraction. The safety profile appears similar to the rate recently described with power sheaths.

Funding Acknowledgement

Type of funding source: None

Society of pediatric liver transplantation: Current registry status 2011-2018

BACKGROUND

SPLIT was founded in 1995 in order to collect comprehensive prospective data on pediatric liver transplantation, including waiting list data, transplant, and early and late outcomes. Since 2011, data collection of the current registry has been refined to focus on prospective data and outcomes only after transplant to serve as a foundation for the future development of targeted clinical studies.

OBJECTIVE

To report the outcomes of the SPLIT registry from 2011 to 2018.

METHODS

This is a multicenter, cross-sectional analysis characterizing patients transplanted and enrolled in the SPLIT registry between 2011 and 2018. All patients, <18 years of age, received a first liver-only, a combined liver-kidney, or a combined liver-pancreas transplant during this study period.

RESULTS

A total of 1911 recipients from 39 participating centers in North America were registered. Indications included biliary atresia (38.5%), metabolic disease (19.1%), tumors (11.7%), and fulminant liver failure (11.5%). Greater than 50% of recipients were transplanted as either Status 1A/1B or with a MELD/PELD exception score. Incompatible transplants were performed in 4.1%. Kaplan-Meier estimates of 1-year patient and graft survival were 97.3% and 96.6%. First 30 days of surgical complications included reoperation (31.7%), hepatic artery thrombosis (6.3%), and portal vein thrombosis (3.2%). In the first 90 days, biliary tract complications were reported in 13.6%. Acute cellular rejection during first year was 34.7%. At 1 and 2 years of follow-up, 39.2% and 50.6% had normal liver tests on monotherapy (tacrolimus or sirolimus). Further surgical, survival, allograft function, and complications are detailed.

P1018Evolution of atrioventricular conduction disorders after TAVI

Background

The evolution of atrioventricular block (AVB) after Trans Aortic Valve Implantation (TAVI) is poorly understood, and indications of pacemaker (PM) implantation after TAVI not well defined. Modern PM algorithms can help studying the evolution of these AV conduction disorders after TAVI. SafeR® mode (Sorin® PM) allows to monitor precisely the AV conduction and to store AVB episodes in the PM memory as intracardiac electrograms, which can be re-read and validated afterwards.

Methods

From November 2015 and January 2017, all patients implanted in one of the 19 French enrolling centers with a Sorin® PM set in SafeR® mode after TAVI could be prospectively included in the study. All the PM interrogation files were centrally collected. The primary endpoint (PE) was the presence of at least one episode of high grade AVB (HG-AVB) beyond day 7 (D7) to one year after the TAVI. It could be validated either by the presence of a HG-AVB on EKG or telemetry, or by the confirmation of a HG-AVB in the PM memory files.

Results

273 patients were included in the study, the PE was assessable in 197 patients. PE was validated in 74.6% patients. In univariate analysis, the use of an oversized prothesis or balloon, and all early episodes of HG-AVB (all those occurring up to D7) influence the validation of the PE. Other AV conduction disorders have no influence on the PE (Table). In multivariate analysis, only HG-AVB occurring between D2 and D7 has a significant influence on the PE.

Factors influencing HG-AVB after TAVI Studied factor HG-AVB episode(s) during the one year follow up No HG-AVB episode during the one year follow up p value RBBB before TAVI (%) 41 34 0,346 Low implantation (>6mm) (%) 59 37 0,156 Use of Autoexpansive Valve (%) 62 62 0,990 Oversizing (%) 19 6 0,022 HG-AVB per TAVI (%) 56 30 0,001 HG-AVB D0-D1 (%) 53 24 0,001 HG-AVB D2-D7 (%) 68 34 0,001 New or wiser LBBB and improvement of PR interval after TAVI (%) 30 39 0,253 Influence of predefined factors on the Primary Endpoint.

Conclusion

The analysis of the SafeR® algorithm files in patients implanted with a PM after TAVI show a high incidence of HG-AVB during the one year follow up. In multivariate analysis, only HG-AVB occurring between D2 and D7 significantly influence the PE, confirming that AV conduction disorders occurring during the first 24 hours may spontaneously normalize.

Acknowledgement/Funding

Microport CRM

Transfer characteristics of subretinal visual implants: corneally recorded implant responses

PURPOSE

The subretinal Alpha IMS visual implant is a CE-approved medical device for restoration of visual functions in blind patients with end-stage outer retina degeneration. We present a method to test the function of the implant objectively in vivo using standard electroretinographic equipment and to assess the devices' parameter range for an optimal perception.

METHODS

Subretinal implant Alpha IMS (Retina Implant AG, Reutlingen, Germany) consists of 1500 photodiode-amplifier-electrode units and is implanted surgically into the subretinal space in blind retinitis pigmentosa patients. The voltages that regulate the amplifiers' sensitivity (V _gl) and gain (V _bias), related to the perception of contrast and brightness, respectively, are adjusted manually on a handheld power supply device. Corneally recorded implant responses (CRIR) to full-field illumination with long duration flashes in various implant settings for brightness gain (V _bias) and amplifiers' sensitivity (V _gl) are measured using electroretinographic setup with a Ganzfeld bowl in a protocol of increasing stimulus luminances up to 1000 cd/m².

RESULTS

CRIRs are a meaningful tool for assessing the transfer characteristic curves of the electronic implant in vivo monitoring the implants' voltage output as a function of log luminance in a sigmoidal shape. Changing the amplifiers' sensitivity (V _gl) shifts the curve left or right along the log luminance axis. Adjustment of the gain (V _bias) changes the maximal output. Contrast perception is only possible within the luminance range of the increasing slope of the function.

CONCLUSIONS

The technical function of subretinal visual implants can be measured objectively using a standard electroretinographic setup. CRIRs help the patient to optimise the perception by adjusting the gain and luminance range of the device and are a useful tool for clinicians to objectively assess the function of subretinal visual implants in vivo.

In vivo biocompatibility of a new cyanine dye for ILM peeling

PURPOSE

To investigate the biocompatibility of the new cyanine dye: 3,3'-Di-(4-sulfobutyl)-1,1,1',1'-tetramethyl-di-1H-benz[e]indocarbocyanine (DSS) as a vital dye for intraocular application in an in vivo rat model and to evaluate the effects of this dye on retinal structure and function.

METHODS

DSS at a concentration of 0.5% was applied via intravitreal injections to adult Brown Norway rats with BSS serving as a control. Retinal toxicity was assessed 7 days later by means of retinal ganglion cell (RGC) counts, light microscopy, optical coherence tomography (OCT), and electroretinography (ERG).

RESULTS

No significant decrease in RGC numbers was observed. No structural changes of the central retina were observed either in vivo (OCT) or under light microscopy. ERGs detected a temporary reduction of retinal function 7 days after injection; this was no longer evident 14 days after injection.

CONCLUSIONS

DSS showed good biocompatibility in a well-established experimental in vivo setting and may be usable for intraocular surgery as an alternative to other cyanine dyes. In contrast to indocyanine green, it additionally offers fluorescence in the visual spectrum. Further studies with other animal models are needed before translation into clinical application.

Enzyme replacement therapy for mucopolysaccharidosis VI: long-term cardiac effects of galsulfase (Naglazyme®) therapy

Characteristic cardiac valve abnormalities and left ventricular hypertrophy are present in untreated patients with mucopolysaccharidosis type VI (MPS VI). Cardiac ultrasound was performed to investigate these findings in subjects during long-term enzyme replacement therapy (ERT) with recombinant human arylsulfatase B (rhASB, rhN-acetylgalactosamine 4-sulfatase, galsulfase, Naglazyme®). Studies were conducted in 54 subjects before ERT was begun and at specific intervals for up to 96 weeks of weekly infusions of rhASB at 1 mg/kg during phase 1/2, phase 2, and phase 3 trials of rhASB. At baseline, mitral and aortic valve obstruction was present and was significantly greater in those ≥12 years of age. Mild mitral and trace aortic regurgitation were present, the former being significantly greater in those <12 years. Left ventricular hypertrophy, with averaged z-scores ranging from 1.6-1.9 SD greater than normal, was present for ages both <12 and ≥12 years. After 96 weeks of ERT, ventricular septal hypertrophy regressed in those <12 years. For those ≥12 years, septal hypertrophy was unchanged, and aortic regurgitation increased statistically but not physiologically. Obstructive gradients across mitral and aortic valves remained unchanged. The results suggest that long-term ERT is effective in reducing intraventricular septal hypertrophy and preventing progression of cardiac valve abnormalities when administered to those <12 years of age.

Influence of simulated weightlessness on the rate of anomalies of the flour beetle Tribolium confusum

Experiments with Tribolium confusum showed that the morphological characteristics of the beetles are modified by simulated weightlessness (fast running clinostat). Because of possible side effects due to differences in fertility of inbred lines, the first experiments were made with a genetically heterogeneous stock. Thereafter experiments were confirmed with inbred beetles. For both stocks a rise of mainly wing anomalies resulted from rotation of whole cultures of beetles within horizontal tubes. The extent to which these anomalies are teratogenetic or genetic has not yet been analysed in detail.

Remodeling of the bifurcation asymmetry of right coronary ventricular branches in hypertrophy

To document the remodeling of the asymmetric branching pattern of the coronary right ventricular branches (RVBs) in right ventricular hypertrophy (RVH), we computed an asymmetry ratio, S, for the diameters and lengths of all vessels, defined as the ratio of the daughter diameters and lengths, respectively. We have previously induced RVH in pigs by pulmonary stenosis for five weeks. At autopsy, silicone elastomer casts of the right coronary arteries were made and the morphometric data on the branching pattern and vascular geometry of the RVB were collected. Data on smaller vessels were obtained from histological specimens while data on larger vessels were obtained from vascular casts. The results show that the diameter asymmetry ratio was significantly decreased in RVH hearts. The asymmetry ratios of diameters and lengths were used to compute the asymmetry ratios for vascular resistance and flow of the various daughter vessels. It was found that the degree of asymmetry of the resistance and flow were decreased, which implies that the flow heterogeneity at a bifurcation is decreased in the RVH hearts.

Evaluation of bleomycin-induced chromosome aberrations under simulated microgravity conditions in human lymphocytes using "FISH" techniques

In the present investigation we report the effects of simulated microgravity conditions (clinostat) on the induction of chromosomal aberrations in human lymphocytes in vitro by (R) Bleomycin. Chromosomal aberrations have been analysed by means of fluorescent in situ hybridisation (FISH) and chromosome-specific composite DNA probes (chromosome painting). The results obtained show that, under simulated microgravity conditions, the levels of both symmetrical and asymmetrical (dicentrics, rings), the number of cells bearing "complex" aberrations and hence the total numbers of aberrations were significantly elevated at any of the dose-levels assayed, compared to the parallel treatments performed as 1g control ("ground"). Furthermore, the ratio symmetrical:asymmetrical translocations was markedly elevated under simulated microgravity conditions, compared to the findings usually observed under "normal" 1g conditions. On these bases, we are much inclined to believe that simulated microgravity, rather than limiting the resealing of DNA double strand breaks (DSB's) induced by genotoxic agents is influencing in terms of enhancement the misrejoining of DSB's which is actually responsible for the fixation of the original lesions to DNA into chromosomal aberrations. In addition, the possible different misrepair processes leading to the formation of symmetrical and asymmetrical translocations might be differentially influenced by microgravity being the symmetrical translocations significantly more represented.

Functional weightlessness during clinorotation of cell suspensions

A clinostat is a device often used in gravitational biology studies. Selecting an appropriate speed of rotation, however, is a frequently debated topic, particularly for suspended cells. In an attempt to define the necessary criteria for determining an acceptable revolution speed, the primary forces governing particle behavior during clinorotation--gravity, diffusion and centrifugation--were mathematically assessed. In support of the theoretical exercise, bacterial growth experiments indicated that results obtained using a clinostat followed trends resembling previous space flight results. It is suspected that this is due, in part at least, to similarly altered external transport processes in each environment.

Effects of gravity on early development

The development of embryonic and larval stages of the South African Toad Xenopus laevis D, was investigated in hyper-g up to 5 g (centrifuge), in simulated 0 g (fast-rotating clinostat), in alternating low g, hyper-g (parabolic flights) and in microgravity (Spacelab missions D1, D-2). The selected developmental stages are assumed to be very sensitive to environmental stimuli. The results showed that the developmental reaction processes run normal also in environments different to 1 g and that aberrations in behavior and morphology normalize after return to 1 g. Development, differentiation, and morphology of the gravity perceiving parts of the vestibular system (macula-organs) had not been affected by exposure to different g-levels.

Longitudinal position matrix of the pig coronary vasculature and its hemodynamic implications

Hemodynamic analysis of coronary blood flow must be based on a statistically valid geometric model of the coronary vasculature. We have previously developed a diameter-defined Strahler model for the arterial and venous trees and a network model for the capillaries. A full set of data describing the geometric properties of the porcine coronary vasculature was given. The order number, diameter, length, connectivity matrix [m,n] (CM), and parallel-series features were measured for all orders of vessels of the right coronary artery (RCA), left anterior descending artery (LAD), left circumflex artery (LCX), and coronary venous system. The purpose of the present study is to present another feature of the branching pattern of the coronary vasculature: the longitudinal position matrix [m,n] (LPM), whose component in row m and column n is the fractional longitudinal position of the branch point on vessels of order n at which vessels of order m branch off (m < or = n). The LPM of the pig RCA, LAD and LCX arterial trees, as well as the coronary sinusal and thebesian venous trees, are presented. The hemodynamic implications of the LPM are illustrated by comparing two kinds of circuits: one, the CM + LPM model, simulates the mean data on the morphology (diameters, lengths, and numbers), CM, and LPM of vessels, whereas the other, the CM model, simulates the mean data on the morphology and CM without considering the LPM. We found that the LPM affects the hemodynamics of coronary blood flow especially with regard to the nonuniformity or dispersion of flow distribution.

Gravity dependency of the gramicidin A channel conductivity. A model for gravity perception on the cellular level

Theoretical investigations involving the membrane-solution interface have revealed that the density of the solution varies appreciably within interfacial layers adjacent to charged membrane surfaces. The hypothesis that gravity interacts with this configuration and modifies transport rates across horizontal and vertical membranes differently was supported by initial experiments with gramicidin A channels in phosphatidylserine (PS) membranes in 0.1 M KCl. Channel conductivity was found to be about 1.6 times higher in horizontal membranes than in vertical membranes. Here we present the results of further experiments with gramicidin A channels (incorporated into charged PS- and uncharged phosphatidylcholine (PC) membranes in KCl- and CsCl-solutions) to demonstrate that the hypothesis is more generally applicable. Again, channel conductivity was found to be higher in horizontal PS membranes by a factor of between 1.20 and 1.75 in 0.1 M CsCl. No difference in channel conductivity was found for uncharged PC membranes in 0.1 M KCl and in 0.1 M CsCl. However, for PC membranes in 0.05 M KCl the channel conductivity was significantly higher in horizontal membranes by a factor of between 1.07 and 1.14. These results are consistent with the results of our model calculations of layer density and extension, which showed that the layer formation is enhanced by increasing membrane surface charge and decreasing electrolyte ion concentration. The mechanism of gravity interaction with membrane transport processes via interface reactions might be utilized by biological systems for orientational behaviour in the gravity field, which has been observed even for cellular systems.

Early development in aquatic vertebrates in near weightlessness during the D-2 Mission STATEX project

Aboard the German-Spacelab-Mission D-2 the project "Gravity Perception and Neuronal Plasticity (STATEX II)" was performed. STATEX is for STATolith EXperiment. Objects were growing tadpoles of the South African Toad (Xenopus laevis D.) and a juvenile cichlid fish (Oreochromis mossambicus). The results give a broader base for the understanding of how environmental stimuli (e.g. linear accelerations) affect the development and function of the gravity perceiving systems in these two vertebrates. These systems are accepted as models for the human vestibulum. Results of experiments in hyper-g (up to 5 g), simulated weightlessness (Fast-rotating-clinostat) and parabolic flights are compared and discussed.

Gravity effects on membrane processes

Application of the Gouy-Chapman-Debye-Hückel (GCDH) theory to a model membrane in contact with electrolytes of various concentrations and composition predict density variations within an interfacial layer. Assuming that on cellular dimensions hydrodynamics can be applied (the objections are briefly discussed) two types of gravity effects can be defined, 1. convection along the surface of vertically oriented membranes and 2. surface potential variations by layer deformations at horizontally oriented membranes. Both effects should affect transport across the layer to the membrane surface and across the membrane. According to the theoretical predictions first experiments with gramicidin channels incorporated into artificial phosphatidylserine bilayer membranes show a significant difference in single channel currents in vertical and horizontal membranes. The complexity of biological membrane functions requires investigation of isolated membrane surface reactions and transport systems to study the gravisensitivity for each process separately.

The reaction of Xenopus laevis Daudin (South African toad) to linear accelerations

Preparing the German Spacelab Mission D-2 project "Gravity Perception and Neuronal Plasticity"--STATEX II--ground based experiments have been performed with larvae of the amphibian vertebrate Xenopus laevis Daud. to study the reactions to different levels of acceleration forces and profiles. The larvae have been exposed to accelerations of up to 5 g for different time periods using a modified laboratory centrifuge and the NIZEMI (Niedergeschwindigkeits-Zentrifugen-Mikroskop) which allows direct observation and video documentation. The results will be discussed and compared with those of the D1-Mission, parabolic flights, and simulated weightlessness.

Gravity effects on biological systems

Theoretical investigations of the membrane-solution interface predict different effects of gravity on vertically and horizontally oriented planar membranes. Single channel events of gramicidin incorporated into phosphatidylserine planar bilayer membranes were measured in 0.1 M KCl solution, pH 7, at room temperature. The potential difference across the membrane was set to +/- 70 mV. The mean channel current was observed to be about 20% higher in horizontally oriented membranes compared to vertical membranes. This is in good agreement with the theoretical considerations and demonstrates that gravity does affect membrane processes by interaction with the membrane-solution interface which is a ubiquitous structure in biological systems.

Gravity and the membrane-solution interface: theoretical investigations

The theory of concentration and potential variations at interfaces is applied to the membrane-solution interface to calculate density variations. The theory is modified to take care of the finite ion volumes in electrolytes. Our model is a phospholipid membrane with a surface charge density of -4.824*10(-6)(As/cm2) in contact with solutions of KCl, NaCl, CaCl2, and mixtures. Maximal density variations of about 4*10(-2)(G/cm3) were found in surface layers between the membrane and the solutions. The extension of the layers is in the range of 1 to 6 nm.