Increased expression of Filaggrin and Claudin-1 in the ocular surface of patients with atopic dermatitis.

BACKGROUND: Atopic dermatitis (AD) is an itchy, chronic and inflammatory skin condition, with dysfunctional immune response and skin barrier defects. Reduction of filaggrin (FLG) and tight junctions (TJ) proteins, such as claudin-1 (CLDN-1), expression in cutaneous epithelial barrier is remarkable in AD pathogenesis. Ocular involvement occurs in approximately 40% of AD patients leading to changes in the structure of the conjunctiva. OBJECTIVES: We aimed to evaluate the expression of FLG and CLDN-1 in the ocular surface of adults with AD, analysing bulbar conjunctival cells collected by a novel non-invasive cellular imprint. METHODS: Bulbar conjunctival epithelial cells were collected by cellular imprint technique, and FLG and CLDN-1 expression were assessed by immunofluorescence (IF) and real-time polymerase chain reaction (RT-PCR). RESULTS: We detected increased expression of FLG and CLDN-1, as well as their transcript levels in AD patients compared with healthy controls (HC). There was a positive correlation between tear film break-up time (TBUT) and FLG expression. Fluorescein staining was inversely associated with FLG expression. CONCLUSIONS: Our results may reflect a reactive response of the ocular surface to AD-related ocular inflammation and associated dry eye disease. Further investigations focusing on the role of FLG and TJ expression in the ocular surface of AD patients may increment the understanding of the pathophysiology of extracutaneous AD and developing future targeted therapies.

A position paper on the management of itch and pain in atopic dermatitis from the International Society of Atopic Dermatitis (ISAD)/Oriented Patient-Education Network in Dermatology (OPENED) task force.

Atopic dermatitis (AD) is a disease that can have a high impact on quality of life, especially due to itch and skin pain. This paper utilizes expertise from members of the International Society of Atopic Dermatitis (ISAD)/Oriented Patient-Education Network in Dermatology (OPENED) task force to review the epidemiology, pathophysiology and exacerbating factors of itch and pain in atopic dermatitis. General principles of treatment are provided, as well as a more detailed evaluation of topical and systemic therapies. Educational and psychological approaches to itch and pain in atopic dermatitis are proposed, along with expert recommendations for the management of itch and pain in atopic dermatitis.

Profile of skin barrier proteins (filaggrin, claudins 1 and 4) and Th1/Th2/Th17 cytokines in adults with atopic dermatitis.

BACKGROUND: Atopic dermatitis (AD) in adults and profile of skin barrier proteins and inflammatory cytokines. OBJECTIVE: Evaluation of the expression of skin barrier proteins such as filaggrin, claudins 1 and 4 and of circulating inflammatory cytokines (Th1/Th2/Th17) in adults with AD. METHODS: Thirty-three adult patients with AD diagnosed according to the Hanifin & Rajkacriteria, and 25 healthy controls were enrolled in the study. AD severity was measured by Eczema Area and Severity Index (EASI). Laboratory assays included immunohistochemistry analysis of skin barrier proteins, such as filaggrin, claudins 1 and 4 and interleukin-17 (IL-17) from skin samples and determination of circulating cytokine levels (IL-2, 4, 5, 6, 10, 17A, TNF and IFN-γ) by flow cytometry (Cytometric Bead Array). RESULTS: We observed a reduced expression of filaggrin and claudin 1 in lesional skin of AD patients, when compared to controls. There was an inverse correlation of filaggrin expression and disease severity. In addition, IL-17 expression was enhanced in AD patients. Similarly, higher levels of inflammatory cytokines (IL-2, 5, 6, 10, 17A and IFN-γ) were found in AD patients. CONCLUSION: Our data reinforce the role of an altered skin barrier in the pathogenesis of AD. Our results show not only reduced expression of filaggrin and claudin 1 in lesional atopic skin but also inverse correlation of filaggrin expression and disease severity. Moreover, elevation of in situ IL-17 and of circulating interleukin levels in AD emphasize the systemic, inflammatory profile of this defective skin barrier dermatosis.

The treatment of sinusitis following maxillary sinus grafting with the association of functional endoscopic sinus surgery (FESS) and an intra-oral approach.

AIM OF THE STUDY: To present the results of a prospective study on the management of infectious complications following maxillary sinus floor elevation procedures with a combined endoscopic (FESS) and intra-oral approach. MATERIALS AND METHODS: From 2005 to 2009, twenty consecutive patients were diagnosed for sinusal chronic infectious complications refractory to medical treatment following maxillary sinus floor elevation and grafting procedures. All patients were treated with a combination of functional endoscopic sinus surgery (FESS) through a transnasal approach and an intra-oral approach, performed by an ear, nose, and throat team and an oral and maxillofacial team, respectively, in the same surgical session under general anesthesia. RESULTS: In 16 of 20 patients, the 4-week endoscopic control demonstrated a complete clinical healing and recovery of the normal sinus ventilation and drainage. In two patients, the persisting sinusitis at the 4-week control was successfully treated (8th week) with an antibiotic therapy based on the antibiogram carried out on the bacterial culture obtained by the aspiration of the sinusal content. In one patient, the persisting sinusitis (3 months after surgery) was successfully treated with the aspiration of the infectious material from the maxillary sinus. In one patient, finally, it was necessary to perform a second combined surgical treatment to treat the persisting sinusitis. DISCUSSION AND CONCLUSIONS: In this study, a relevant number of cases of chronic infectious complications following sinus floor elevation procedures are presented. To the authors' knowledge, it is the first time that well-defined treatment protocols based on a combined endoscopic (FESS) and intra-oral surgical approach are proposed. The positive, albeit preliminary, results obtained in this study seem to validate this treatment modality.

Heterogeneity of intrinsic repolarization properties within the human heart: new insights from simulated three-dimensional current surfaces.

Heterogeneity of repolarization properties is pivotal for both physiology and pathology of the heart and mathematical models of different cardiac cell types that are tuned to experimental data in order to reproduce it in silico. Repolarization heterogeneity is described most of the times with reference to one or the other of the many repolarization parameters, like action potential (AP) form and duration, or the maximum conductance of a given ion current, which are nonlinearly connected and frequently overdetermined. A compact representation of models dynamics would help their standardization, their use, and the understanding of the underlying physiology. A 3-D representation of cardiac AP derived from the measure of instantaneous current-voltage relationships during repolarization has been previously described. Here, it is shown that such a representation compactly summarizes important features of repolarization which are relevant particularly for what concerns its electrotonic modulation within the human heart. It is found that, according to the tested models, late phase of AP repolarization displays autoregenerativity only within the ventricle, and that this property is heterogeneously distributed across the wall. Three-dimensional current representations of the AP also provide precise estimation of the time course of membrane resistance, which changes throughout the heart, and can be used to predict entrainment of repolarization during AP propagation.

Titanium-zirconium alloy narrow-diameter implants (Straumann Roxolid(®)) for the rehabilitation of horizontally deficient edentulous ridges: prospective study on 18 consecutive patients.

AIM OF THE STUDY: (i) To evaluate the survival and success rates of the new Roxolid narrow diameter implant placed in horizontally deficient ridges; and (ii) to evaluate the incidence of prosthetic complications. MATERIALS AND METHODS: In a 24-month period (2009-2010) 18 partially or totally edentulous patients received 51 Straumann Roxolid (13 tissue level, 38 bone level) implants. Prosthetic loading of implants was either immediate (four implants; one patient) or delayed (2-12 months after placement; 47 implants; 17 patients). The patients were rehabilitated with either fixed (16 patients; 45 implants) or removable (two patients; six implants) prostheses. RESULTS: All implants successfully achieved osseointegration and all patients completed the planned prosthetic rehabilitation. Peri-implant bone resorption values ranged from 0 to 1 mm at the end of the observation period (range: 3-19 months). Implant survival and success rates were therefore 100%. No prosthetic complications occurred and all implants are still in function; therefore the prosthesis success rate was 100%. CONCLUSION: Narrow diameter implants fabricated with the new titanium-zirconium alloy were demonstrated to be reliable in supporting both fixed and removable prosthetic rehabilitations in horizontally deficient ridges. Implant survival, peri-implant bone resorption, and prosthetic complication rates were consistent with those reported in the literature for standard diameter implants placed in non-deficient edentulous ridges.

3D current-voltage-time surfaces unveil critical repolarization differences underlying similar cardiac action potentials: A model study.

The number of mathematical models of cardiac cellular excitability is rapidly growing, and compact graphical representations of their properties can make new acquisitions available for a broader range of scientists in cardiac field. Particularly, the intrinsic over-determination of the model equations systems when fitted only to action potential (AP) waveform and the fact that they are frequently tuned on data covering only a relatively narrow range of dynamic conditions, often lead modellers to compare very similar AP profiles, which underlie though quite different excitable properties. In this study I discuss a novel compact 3D representation of the cardiac cellular AP, where the third dimension represents the instantaneous current-voltage profile of the membrane, measured as repolarization proceeds. Measurements of this type have been used previously for in vivo experiments, and are adopted here iteratively at a very high time, voltage, current-resolution on (i) the same human ventricular model, endowed with two different parameters sets which generate the same AP waveform, and on (ii) three different models of the same human ventricular cell type. In these 3D representations, the AP waveforms lie at the intersection between instantaneous time-voltage-current surfaces and the zero-current plane. Different surfaces can share the same intersection and therefore the same AP; in these cases, the morphology of the current surface provides a compact view of important differences within corresponding repolarization dynamics. Refractory period, supernormal excitability window, and extent of repolarization reserve can be visualized at once. Two pivotal dynamical properties can be precisely assessed, i.e. all-or-nothing repolarization window and membrane resistance during recovery. I discuss differences in these properties among the membranes under study, and show relevant implications for cardiac cellular repolarization.

Bronchodilator activity of (3R)-3-[[[(3-fluorophenyl)[(3,4,5-trifluorophenyl)methyl]amino] carbonyl]oxy]-1-[2-oxo-2-(2-thienyl)ethyl]-1-azoniabicyclo[2.2.2]octane bromide (CHF5407), a potent, long-acting, and selective muscarinic M3 receptor antagonist.

The novel quaternary ammonium salt (3R)-3-[[[(3-fluorophenyl)[(3,4,5-trifluorophenyl)methyl]amino]carbonyl]oxy]-1-[2-oxo-2-(2-thienyl)ethyl]-1-azoniabicyclo[2.2.2]octane bromide (CHF5407) showed subnanomolar affinities for human muscarinic M1 (hM1), M2 (hM2), and M3 (hM3) receptors and dissociated very slowly from hM3 receptors (t(½) = 166 min) with a large part of the receptorial complex (54%) remaining undissociated at 32 h from radioligand washout. In contrast, [(3)H]CHF5407 dissociated quickly from hM2 receptors (t(½) = 31 min), whereas [(3)H]tiotropium dissociated slowly from both hM3 (t(½) = 163 min) and hM2 receptor (t(½) = 297 min). In the guinea pig isolated trachea and human isolated bronchus, CHF5407 produced a potent (pIC(50) = 9.0-9.6) and long-lasting (up to 24 h) inhibition of M3 receptor-mediated contractile responses to carbachol. In the guinea pig electrically driven left atrium, the M2 receptor-mediated inhibitory response to carbachol was recovered more quickly in CHF5407-pretreated than in tiotropium-pretreated preparations. CHF5407, administered intratracheally to anesthetized guinea pigs, potently inhibited acetylcholine (Ach)-induced bronchoconstriction with an ED(50) value of 0.15 nmol/kg. The effect was sustained over a period of 24 h, with a residual 57% inhibition 48 h after antagonist administration at 1 nmol/kg. In conscious guinea pigs, inhaled CHF5407 inhibited Ach-induced bronchoconstriction for at least 24 h as did tiotropium at similar dosages. Cardiovascular parameters in anesthetized guinea pigs were not significantly changed by CHF5407, up to 100 nmol/kg i.v. and up to 1000 nmol/kg i.t. In conclusion, CHF5407 shows a prolonged antibronchospastic activity both in vitro and in vivo, caused by a very slow dissociation from M3 receptors. In contrast, CHF5407 is markedly short-acting at M2 receptors, a behavior not shared by tiotropium.

Inflammatory bowel disease in children and adolescents in Italy: data from the pediatric national IBD register (1996-2003).

BACKGROUND: The purpose was to assess in Italy the clinical features at diagnosis of inflammatory bowel disease (IBD) in children. METHODS: In 1996 an IBD register of disease onset was established on a national scale. RESULTS: Up to the end of 2003, 1576 cases of pediatric IBD were recorded: 810 (52%) ulcerative colitis (UC), 635 (40%) Crohn's disease (CD), and 131 (8%) indeterminate colitis (IC). In the period 1996-2003 an increase of IBD incidence from 0.89 to 1.39/10(5) inhabitants aged <18 years was observed. IBD was more frequent among children aged between 6 and 12 years (57%) but 20% of patients had onset of the disease under 6 years of age; 28 patients were <1 year of age. Overall, 11% had 1 or more family members with IBD. The mean interval between onset of symptoms and diagnosis was higher in CD (10.1 months) and IC (9 months) versus UC (5.8 months). Extended colitis was the most frequent form in UC and ileocolic involvement the most frequent in CD. Upper intestinal tract involvement was present in 11% of CD patients. IC locations were similar to those of UC. Bloody diarrhea and abdominal pain were the most frequent symptoms in UC and IC, and abdominal pain and diarrhea in CD. Extraintestinal symptoms were more frequent in CD than in UC. CONCLUSIONS: The IBD incidence in children and adolescents in Italy shows an increasing trend for all 3 pathologies. UC diagnoses exceeded CD.

Metabolic treatment of critically ill patients: energy expenditure and energy supply.

Nutrition in critically ill patients should be considered as therapy: assessing the energy expenditure and the termogenic effect of food, and knowing the differences among composition and amount of given substrates, it is possible restore, maintain, or at least limit the derangement of energy equilibrium. Energy metabolism comprehends assumption, storage and oxidation of nutrients: all these factors could be discriminant in critical clinical conditions, particularly cardiac and respiratory failure. Then, this review would lead the decision making process beginning from biochemistry and bioenergetics, until the metabolic strategy practically usable at the bedside of patients during the whole critical phase of their pathology.

Effect of input resistance voltage-dependency on DC estimate of membrane capacitance in cardiac myocytes.

The measure of membrane capacitance (C(m)) in cardiac myocytes is of primary importance as an index of their size in physiological and pathological conditions, and for the understanding of their excitability. Although a plethora of very accurate methods has been developed to access C(m) value in single cells, cardiac electrophysiologists still use, in the majority of laboratories, classical direct current techniques as they have been established in the early days of cardiac cellular electrophysiology. These techniques are based on the assumption that cardiac membrane resistance (R(m)) is constant, or changes negligibly, in a narrow potential range around resting potential. Using patch-clamp whole-cell recordings, both in current-clamp and voltage-clamp conditions, and numerical simulations, we document here the voltage-dependency of R(m), up to -45% of its resting value for 10-mV hyperpolarization, in resting rat ventricular myocytes. We show how this dependency makes classical protocols to misestimate C(m) in a voltage-dependent manner (up to 20% errors), which can dramatically affect C(m)-based calculations on cell size and on intracellular ion dynamics. We develop a simple mechanistic model to fit experimental data and obtain voltage-independent estimates of C(m), and we show that accurate estimates can also be extrapolated from the classical approach.

Improved pore space structure characterization by fusion of relaxation tomography maps.

Quantitative Relaxation Tomography in porous media furnishes maps of internal sections where each pixel represents T1 or T2 of water 1H in the corresponding voxel, so that quantitative information on the pore space structure can be obtained. The porosity can be determined at different length scales by correcting pixel by pixel the signal intensity for T2 decay. Moreover, on the basis of the distribution of T1, the microporosity fraction can be computed, as well as several voxel-average porosities. Since T1 and T2 encode different pieces of information, fusion image techniques can improve the characterization of the pore space, showing simultaneously, on the same image, maps of the two parameters. Examples are given of application to a water-saturated travertine core and to a pig femur. Different kinds of look-up tables were tried by varying two of the three dimensions of the HSV color space in such a way as to optimize both the T1 and T2 contrasts simultaneously.

[The mechanism of impulse initiation: high-resolution epicardial pace-mapping in rat heart]. / Meccanismo di insorgenza del battito stimolato: misura del potenziale epicardico ad alta risoluzione spaziale nel cuore di ratto.

UNLABELLED: Simulations of cardiac tissue bidomain model indicate that point cathodal stimulation gives rise to a dog-bone depolarized region (virtual cathode) extending across fibers, limited by two symmetric hyperpolarized regions (virtual anode) extending along fibers. These predictions were experimentally confirmed by optical mapping studies of transmembrane potentials while no direct validation is reported at the extracellular level. The present study aims at defining the influence of the virtual cathode on extracellular potentials by means of high-density epicardial mapping. METHODS: Epicardial potentials were measured in seven exposed rat hearts by means of a 11 x 11 electrode array with 360 x 540 microns resolution. Cathodal current pulses, 100-200 microA intensity and 1 ms duration, to avoid superposition of stimulus and activation potentials, were delivered from one of the electrode array and unipolar potentials were measured from all other electrodes. RESULTS AND DISCUSSION: a) During stimulus, negative equipotential lines were elliptic along fibers, as expected, but for a 2 mm circular region at the pacing site. b) During 1-2 ms interval between stimulus offset and start of activation, equipotential lines became elliptic across fibers in the presence of the region directly excited by the stimulus field. Start of activation was either symmetric with isochrones initially circular around the pacing site and then elliptic along fibers, or asymmetric initiating at only one side of the pacing site across fibers with isochrones elliptic along fibers. In the latter case, the wave front was blocked through the refractory region directly excited by the stimulus field, subdivided into two wings which collided and merged at the opposite side, giving rise to a plane wave front propagating across fibers away from the pacing site. CONCLUSIONS: High spatial resolution epicardial potential mapping reveals the existence of the virtual cathode and its influence on impulse initiation and conduction. The unexpected existence of a region of conduction block at the pacing site, due to spatial asymmetry of normal cardiac tissue which enhances activation threshold at one of the two sides of the virtual cathode, is intriguing since it is one of the requirements for reentry of conduction in the presence of a circuit with decreased conduction velocity and short duration of refractory period.

Myocardial remodeling and arrhythmogenesis in moderate cardiac hypertrophy in rats.

In 47 male adult Wistar rats with 4-wk aortic coarctation (AC) and 39 age-matched sham-operated rats (SO) chronically instrumented for telemetry electrocardiogram recording, we investigated the mechanisms of arrhythmogenesis in moderate cardiac hypertrophy, with an approach from "in vivo" toward the cellular level, analyzing 1) stress-induced cardiac arrhythmias in all rats and 2) myocardial fibrosis in 35 animals and action potential duration and density of hyperpolarization-activated current in 19 others at the ventricular level. Aortic banding increased arterial blood pressure, cardiac weight, and ventricular myocyte volume by 11, 25, and 14%, respectively (P < 0.001-0.05). Ventricular arrhythmias occurred at similar rates in AC and SO rats throughout the stress procedure. Action potential duration and hyperpolarization-activated current were about twice as great and myocardial fibrosis about four times greater in AC animals (P < 0.005-0.05). Electrocardiogram data also revealed more supraventricular arrhythmias in AC rats during the baseline period and after stress and fewer atrioventricular block episodes after stress (P < 0.05). Thus stress-induced supraventricular and atrioventricular nodal, but not ventricular, arrhythmias were affected in moderate cardiac hypertrophy when ventricular morphofunctional alterations were evident.

[Simultaneous measurements of electrical coupling and action potential transfer in pairs of ventricular cardiomyocytes]. / Misura contemporanea dell'accoppiamento elettrico e della conduzione del potenziale d'azione in coppie di cardiomiociti ventricolari.

Spread and modulation of electrical activity in cardiac tissue requires intercellular transfer of current via gap junctions, specialised regions of densely packed ionic channels. Electrotonic interaction is determined not merely by intercellular electrical resistance (Rj) but rather by the interplay of Rj and sarcolemmal passive and active electrical properties (Zaniboni et al., Spitzer et al.). In this work we combined a well established protocol to measure Rj in cell pairs (Weingart e Maurer) with a stimulation protocol which allowed to simultaneously study parameters relative to action potential transfer during sequential stimulation. Current clamp experiments, performed on cardiomyocyte pairs held in double-patch configuration, allowed to simultaneously monitor, at a relatively high frequency (1 Hz), membrane resistance (Rm), resting potential (Vm), maximum depolarization rate (dv/dtmax) and time to peak of dv/dtmax in both cells as well as Rj. Spontaneous electrical uncoupling was observed in guinea pig cell pairs with little or no effect on action potential transfer. Pharmacological uncoupling with 40 microM beta-glycyrrhetinic acid reached, in one case, a much higher level of Rj and dramatically increased time delay for action potential appearance. When only Rj was measured over a short time interval after approximately two minutes from cell-attachments, values of Rj approximately 40 M omega in rat cell pairs (n = 20) and Rj approximately 15 M omega in guinea pig cell pairs (n = 24) were obtained. The possibility of monitoring simultaneously active and intercellular/cellular passive electrical properties makes this protocol particularly suitable to study dynamic changes in Rj during action potential transfer.

Beat-to-beat repolarization variability in ventricular myocytes and its suppression by electrical coupling.

Single ventricular myocytes paced at a constant rate and held at a constant temperature exhibit beat-to-beat variations in action potential duration (APD). In this study we sought to quantify this variability, assess its mechanism, and determine its responsiveness to electrotonic interactions with another myocyte. Interbeat APD(90) (90% repolarization) of single cells was normally distributed. We thus quantified APD(90) variability as the coefficient of variability, CV = (SD/mean APD(90)) x 100. The mean +/- SD of the CV in normal solution was 2.3 +/- 0.9 (132 cells). Extracellular TTX (13 microM) and intracellular EGTA (14 mM) both significantly reduced the CV by 44 and 26%, respectively. When applied in combination the CV fell by 54%. In contrast, inhibition of the rapid delayed rectifier current with L-691,121 (100 nM) increased the CV by 300%. The CV was also significantly reduced by 35% when two normal myocytes were electrically connected with a junctional resistance (R(j)) of 100 MOmega. Electrical coupling (R(j) = 100 MOmega) of a normal myocyte to one producing early afterdepolarization (EAD) completely blocked EAD formation. These results indicate that beat-to-beat APD variability is likely mediated by stochastic behavior of ion channels and that electrotonic interactions act to limit temporal dispersion of refractoriness, a major contributor to arrhythmogenesis.

Complications associated with rapid caffeine application to cardiac myocytes that are not voltage clamped.

The rapid application of caffeine to cardiac myocytes is commonly used to assess changes in the Ca2+ content of the sarcoplasmic reticulum (SR) and to study other parameters of intracellular Ca2+ regulation. Here we examined the effects of rapid caffeine application on membrane potential, intracellular Ca2+, and cell shortening in ventricular myocytes (rat, rabbit, guinea pig, dog) and atrial myocytes (rabbit) that were not voltage clamped. Conditioning pacing was used to achieve a steady-state level of SR Ca2+ loading prior to caffeine (10 mM) application. Caffeine transiently depolarized myocytes as expected from activation of forward Na+-Ca2+ exchange. However, we also found in each species (50% rat, 36% rabbit ventricular, 53% rabbit atrial, 56% guinea pig, 31% dog) that the caffeine-induced depolarization could also trigger an action potential. Caffeine-triggered potentials were completely blocked by thapsigargin (1 microM). The Ca2+ transient and contraction that accompanied caffeine-triggered action potentials had a larger magnitude and slower rate of decline (or relaxation) than occurred during caffeine-induced subthreshold depolarizations. Thus, the use of rapid caffeine application to study SR function and [Ca2+]i regulation in myocytes that are not voltage clamped can yield erroneous results.

Electrotonic modulation of electrical activity in rabbit atrioventricular node myocytes.

Electrotonic effects of electrically coupling atrioventricular (AV) nodal cells to each other and to real and passive models of atrial and ventricular cells were studied using a technique that does not require functional gap junctions. Membrane potential was measured in each cell using suction pipettes. Mutual entrainment of two spontaneously firing AV nodal cells was achieved with a junctional resistance (Rj) of 500 M omega, which corresponds to only 39 junctional channels, assuming a single-channel conductance of 50 pS. Coupling of AV nodal and atrial cells at Rj of 50 M omega caused hyperpolarization of the nodal cell, decreasing its action potential duration and either slowing or blocking diastolic depolarization in the AV node myocyte. Opposite changes occurred in the atrial action potential. When AV nodal and ventricular cells were coupled at Rj of 50 M omega, nodal diastolic potential was markedly hyperpolarized and diastolic depolarization was completely blocked with little change in ventricular diastolic potential. However, coupling did elicit marked changes in the action potential duration of both cells, with prolongation in the nodal cell and shortening in the ventricular cell. Nodal maximum upstroke velocity was increased by both atrial and ventricular coupling, as expected from the hyperpolarization that occurred. With an Rj of 50 M omega, spontaneous firing was blocked in all single AV nodal pacemaker cells during coupling to a real or passive model of an atrial or ventricular cell. These results demonstrate that action potential formation and waveform in a single AV nodal cell is significantly affected by electrical coupling to other myocytes.