Single Enzyme Nanoparticles with Improved Biocatalytic Activity through Protein Entrapment in a Surfactant Shell

A polymeric corona consisting of an alkyl-glycolic acid ethoxylate (C_XEO_Y) surfactant offers a promising approach toward endowing proteins with thermotropic phase behavior and hyperthermal activity. Typically, preparation of protein–surfactant biohybrids is performed via chemical modification of acidic residues followed by electrostatic conjugation of an anionic surfactant to encapsulate single proteins. While this procedure has been applied to a broad range of proteins, modification of acidic residues may be detrimental to function for specific enzymes. Herein, we report on the one-pot preparation of biohybrids via covalent conjugation of surfactants to accessible lysine residues. We entrap the model enzyme hen egg-white lysozyme (HEWL) in a shell of carboxyl-functionalized C₁₂EO₁₀ or C₁₂EO₂₂ surfactants. With fewer surfactants, our covalent biohybrids display similar thermotropic phase behavior to their electrostatically conjugated analogues. Through a combination of small-angle X-ray scattering and circular dichroism spectroscopy, we find that both classes of biohybrids consist of a folded single-protein core decorated by surfactants. Whilst traditional biohybrids retain densely packed surfactant coronas, our biohybrids display a less dense and heterogeneously distributed surfactant coverage located opposite to the catalytic cleft of HEWL. In solution, this surfactant coating permits 7- or 3.5-fold improvements in activity retention for biohybrids containing C₁₂EO₁₀ or C₁₂EO₂₂, respectively. The reported alternative pathway for biohybrid preparation offers a new horizon to expand upon the library of proteins for which functional biohybrid materials can be prepared. We also expect that an improved understanding of the distribution of tethered surfactants in the corona will be crucial for future structure–function investigations.

Bioinspired Scaffolding by Supramolecular Amines Allows the Formation of One- and Two-Dimensional Silica Superstructures

Silica materials attract an increasing amount of interest in (fundamental) research, and find applications in, for example, sensing, catalysis, and drug delivery. As the properties of these (nano)materials not only depend on their chemistry but also their size, shape, and surface area, the controllable synthesis of silica is essential for tailoring the materials to specific applications. Advantageously, bioinspired routes for silica production are environmentally friendly and straightforward since the formation process is spontaneous and proceeds under mild conditions. These strategies mostly employ amine-bearing phosphorylated (bio)polymers. In this work, we expand this principle to supramolecular polymers based on the water-soluble cationic cyanine dye Pinacyanol acetate. Upon assembly in water, these dye molecules form large, polyaminated, supramolecular fibers. The surfaces of these fibers can be used as a scaffold for the condensation of silicic acid. Control over the ionic strength, dye concentration, and silicic acid saturation yielded silica fibers with a diameter of 25 nm and a single, 4 nm pore. Unexpectedly, other unusual superstructures, namely, nummulites and spherulites, are also observed depending on the ionic strength and dye concentration. Transmission and scanning electron microscopy (TEM and SEM) showed that these superstructures are formed by aligned silica fibers. Close examination of the dye scaffold prior silicification using small-angle X-ray scattering (SAXS), and UV/Vis spectroscopy revealed minor influence of the ionic strength and dye concentration on the morphology of the supramolecular scaffold. Total internal reflection fluorescence (TIRF) during silicification unraveled that if the reaction is kept under static conditions, only silica fibers are obtained. Experiments performed on the dye scaffold and silica superstructures evidenced that the marked structural diversity originates from the arrangement of silica/dye fibers. Under these mild conditions, external force fields can profoundly influence the morphology of the produced silica.

Long-term survival after mitral valve replacement in children aged <5 years: a multi-institutional study

BACKGROUND

Short- and long-term outcomes after prosthetic mitral valve replacement (MVR) in children aged <5 years are ill-defined and generally perceived as poor. The experience of the Pediatric Cardiac Care Consortium (45 centers, 1982 to 1999) was reviewed.

METHODS AND RESULTS

MVR was performed 176 times on 139 patients. Median follow-up was 6.2 years (range 0 to 20 years, 96% complete). Age at initial MVR was 1.9+/-1.4 years. Complications after initial MVR included heart block requiring pacemaker (16%), endocarditis (6%), thrombosis (3%), and stroke (2%). Patient survival was as follows: 1 year, 79%; 5 years, 75%; and 10 years, 74%. The majority of deaths occurred early after initial MVR, with little late attrition despite repeat MVR and chronic anticoagulation. Among survivors, the 5-year freedom from reoperation was 81%. Age-adjusted multivariable predictors of death include the presence of complete atrioventricular canal (hazard ratio 4.76, 95% CI 1.59 to 14.30), Shone's syndrome (hazard ratio 3.68, 95% CI 1.14 to 11.89), and increased ratio of prosthetic valve size to patient weight (relative risk 1.77 per mm/kg increment, 95% CI 1.06 to 2.97). Age- and diagnosis-adjusted prosthetic size/weight ratios predicted a 1-year survival of 91% for size/weight ratio 2, 79% for size/weight ratio 3, 61% for size/weight ratio 4, and 37% for size/weight ratio 5.

CONCLUSIONS

Early mortality after MVR can be predicted on the basis of diagnosis and the size/weight ratio. Late mortality is low. These data can assist in choosing between MVR and alternative palliative strategies.

Is Arrhythmia Detection by Automatic External Defibrillator Accurate for Children?

Background —Use of automatic external defibrillators (AEDs) in children aged <8 years is not recommended. The purpose of this study was to develop an ECG database of shockable and nonshockable rhythms from a broad age range of pediatric patients and to test the accuracy of the Agilent Heartstream FR2 Patient Analysis System for sensitivity and specificity.

Methods and Results —Children aged ≤12 years who either developed arrhythmias or were at risk for developing arrhythmias were studied. Two sources were used for the database: children whose rhythms were recorded prospectively via a modified AED and children who had arrhythmias captured on paper and digitized for subsequent analysis. The rhythms were divided into 5-second strips, classified by 3 reviewers, and then assessed by the AED analysis algorithm. A total of 696 five-second rhythm strips from 191 children (81 female and 110 male) aged 1 day to 12 years (median 3.0 years) were analyzed. There was 100% specificity for nonshockable rhythms. Sensitivity for ventricular fibrillation was 96%.

Conclusions —There was excellent AED rhythm analysis sensitivity and specificity in all age groups for ventricular fibrillation and nonshockable rhythms. The high specificity and sensitivity indicate that there is a very low risk of an inappropriate shock and that the AED correctly identifies shockable rhythms, making the algorithm both safe and effective for children.

Normalization of ventricular repolarization with flecainide in long QT syndrome patients with SCN5A:DeltaKPQ mutation

BACKGROUND

The Long QT Syndrome (LQTS) is a genetic channelopathy with life-threatening implications. The LQT3 form of this disease is caused by mutations of the SCN5A sodium-channel gene. A specific mutation, SCN5A:DeltaKPQ, is associated with repetitive reopenings of the sodium channel and prolonged inward current. This dominant inward current is manifest on the electrocardiogram as QT prolongation. Flecainide is a potent blocker of the open sodium channel.

METHODS AND RESULTS

The effect of flecainide on the duration of the QT-interval and the T-wave morphology was systematically evaluated in five male patients age 2-64 years having the SCN5A:DeltaKPQ mutation. After baseline electrocardiograms were obtained, low-dose oral flecainide was administered for 48 hours. Serial electrocardiograms and blood flecainide levels were obtained during flecainide therapy. The QTc interval decreased on average by 104 ms, from a baseline value of 565 +/- 60 ms to 461 +/- 23 ms (P < 0.04) at a mean flecainide level of 0.28 +/- 0.08 mg/L, with shortening of the QTonset interval (P < 0.003) and normalization of T-wave morphology. The effects of flecainide were compared with oral mexiletine in two patients, with flecainide showing greater QTc shortening and more complete normalization of repolarization. No adverse side effects or proarrhythmia were observed with flecainide in this study.

CONCLUSION

Low-dose, oral flecainide consistently shortened the QTc interval and normalized the repolarization T-wave pattern in five LQT3 patients with SCN5A:DeltaKPQ mutation. This preliminary study indicates that low-dose flecainide is a promising therapeutic agent for LQTS patients with the SCN5A:DeltaKPQ sodium channel mutation.

A soluble neuronal factor alters contractile function of ventricular myocytes without effect on troponin T isoform expression

OBJECTIVE

The purpose of this investigation was to establish a model system to facilitate identification of the sympathetic neuronal factor(s) that promotes improved contractility in neonatal cardiac myocytes. Conditioned medium from PC12 cells with sympathetic phenotype served as the source of the neuronal factor.

METHODS

Contraction frequency, amplitude and velocity of cultured neonatal rat cardiac myocytes were measured by online video analysis. Interventions included in vitro sympathetic innervation, exposure to PC12 conditioned medium, neurotransmitters and antagonists. Metabolic activity was assayed by 2-deoxyglucose uptake. Troponin T isoform expression was analyzed by SDS-polyacrylamide gel electrophoresis.

RESULTS

Medium conditioned by neuronal PC12 cells induced contractility changes similar to those induced by in vitro sympathetic innervation. These effects of PC12 conditioned medium and innervation were not suppressed by adrenergic or muscarinic antagonists nor reproduced by neuropeptide Y or somatostatin. Neuronal PC12 conditioned medium but not chromaffin PC12 conditioned medium, increased metabolic activity of the myocytes as detected by [3H]-2-deoxyglucose, indicating that the effect was specific to the neuronal PC12 cells. The in vitro switch of troponin T isoform expression was not altered by exposure to PC12 conditioned medium.

CONCLUSIONS

Increased contractile function induced by sympathetic innervation is reproduced by PC12 conditioned medium, but neither is mediated by sympathetic or muscarinic neurotransmitters. Troponin T isoform expression is not related to the contractility changes. This model system will allow identification of the factor(s).

Accurate recognition and effective treatment of ventricular fibrillation by automated external defibrillators in adolescents

OBJECTIVES

To evaluate the accuracy and efficacy of automated external defibrillators (AEDs) in patients <16 years old.

BACKGROUND

AEDs are standard therapy in out-of-hospital resuscitation of adults and have led to higher success rates. Their use in children and adolescents has never been evaluated, despite recommendations from the American Heart Association that they be used in children >8 years of age.

METHODS

This was a retrospective cohort study of children <16 years old who underwent out-of-hospital cardiac resuscitation and on whom an AED was used during the resuscitation. The setting was rural and urban prehospital emergency medical systems. Patients were identified by review of a database of cardiac arrests maintained by a large surveillance program of these services.

RESULTS

AEDs were used to assess cardiac rhythm in 18 patients with a mean age of 12.1 +/- 3.7 years. The cardiac rhythms were analyzed 67 times and included ventricular fibrillation (25), asystole/pulseless electrical activity (32), sinus bradycardia (6), and sinus tachycardia (4). The AEDs recognized all nonshockable rhythms accurately and advised no shock. Ventricular fibrillation was recognized accurately in 22 (88%) of 25 episodes and advised or administered a shock 22 times. Sensitivity and specificity for accurate rhythm analysis were 88% and 100%, respectively. One patient with a nonshockable rhythm survived, whereas 3 of 9 patients with ventricular fibrillation survived.

CONCLUSIONS

These data furnish evidence that AEDs provide accurate rhythm detection and shock delivery to children and young adolescents. AED use is potentially as effective for children as it is for adults.

Complete heart block in association with graft-versus-host disease

An infant who received haploidentical BM for severe combined immunodeficiency (SCID) developed acute, reversible complete heart block in association with an exacerbation of GVHD. Respiratory distress and myocardial dysfunction were also seen with this and previous GVHD exacerbations. The patient had not received chemotherapy or radiation prior to BMT. The complete heart block resolved after 1 week of intensive immunosuppression. The association of complete heart block with GVHD is important because the heart block is potentially reversible with prompt, aggressive control of the GVHD.

Common cardiovascular problems in the young: Part II. Hypertension, hypercholesterolemia and preparticipation screening of athletes

Blood pressure should be measured during health maintenance visits in all children three years of age and older. Cholesterol levels should be obtained in children with a family history of hypercholesterolemia or premature coronary artery disease and in children with other risk factors, such as hypertension, smoking or obesity. Preparticipation screening for sports participation should include a detailed questionnaire regarding the athlete's personal or family history of syncope, sudden death or arrhythmia, as well as measurement of blood pressure, auscultation of the heart and evaluation of upper and lower extremity pulses.

Regulation of rat cardiac myocyte growth by a neuronal factor secreted by PC12 cells

Sympathetic innervation of cardiac myocytes in vitro induces growth independent of anatomic contact between the neurons and myocytes and is not mediated by alpha- or beta-adrenergic receptor stimulation. To establish a model system that will allow purification and identification of the neuronal factor(s) responsible for mediating this regulation, we have initiated studies utilizing conditioned medium from the PC12 cell line. PC12 cells acquire a cholinergic sympathetic neuronal phenotype when exposed to nerve growth factor. Culture medium conditioned by neuronal PC12 cells, but not nonneuronal PC12 cells, induces growth in newborn rat cardiac myocytes as measured by surface area and [35S]methionine incorporation into protein and increases expression of atrionatriuretic peptide, a marker for myocyte hypertrophy. The magnitude of the growth response is dose-dependent and mimics the response to sympathetic innervation. The myocyte response to conditioned medium is not detectable after 24 h of exposure; maximal rate of protein synthesis is obtained within 48 h. Neuronally differentiated PC12 cell-conditioned medium stimulation of growth could not be mimicked by alpha- or beta-adrenergic agonists or muscarinic agonists, nor inhibited by alpha- or beta-adrenergic antagonists, nor by muscarinic antagonists. Neuropeptide Y and somatostatin, peptides known to be present in PC12 cells and sympathetic neurons, were also ineffective at reproducing the effect of neuronally differentiated PC12 cell-conditioned medium. These data indicate that neuronal cells release a soluble factor, different from neurotransmitter, which stimulates myocyte growth. They further identify the PC12 cell line as providing a convenient and abundant supply of this molecule, thus facilitating its further characterization.

Operative mortality and frequency of coexistent anomalies in interruption of the aortic arch

Operative mortality for 262 infants with interruption of the aortic arch repaired from 1982 to June 1993 has remained constant at about 35%. Major coexistent cardiac malformations, type B interruption, or staged repair are risk factors for mortality.

A multimodal approach to functional dysphagia

Functional dysphagia in children has historically been treated using a cognitive behavioral approach. The case of a 7-year-old boy treated using a successful multimodal approach, including behavioral, family, and play therapy with alprazolam augmentation, is reported. The patient showed minimal response to early interventions but rapidly improved with the prescription of alprazolam before meals.

Pediatric defibrillation: current flow is improved by using "adult" electrode paddles

OBJECTIVE

Current flow, the major determinant of defibrillation success, depends on delivered energy and transthoracic impedance. Previous experimental data suggest that transthoracic impedance is higher using "pediatric" electrode paddles compared to the larger "adult" electrode paddles. There are few data from actual shocks to support the experimental studies. The purpose of this study was to measure transthoracic impedance during actual shock delivery and to determine the optimal electrode paddle size for pediatric defibrillation and cardioversion.

METHODS

We prospectively evaluated all shocks of < or = 20 joules given to pediatric patients at the University of Iowa from 1988 to 1992. Data collected included energy selected by the operator, energy delivered by the defibrillator, peak current flow and transthoracic impedance. Data were analyzed by unpaired t test and linear regression.

RESULTS

Fifty-five shocks were delivered to 20 patients, age newborn to 8 years. Thirty-seven shocks were given with "pediatric" electrode paddles (surface area 21 cm2) and 18 with "adult" electrode paddles (surface area 83 cm2). Selected energy correlated well with delivered energy (r = .98, P < .0001). Delivered energy using "pediatric" electrodes did not differ from that delivered with "adult" electrodes (8.0 +/- 0.9 joules vs 10.5 +/- 1.2 joules P > .1). However transthoracic impedance was significantly higher with "pediatric" electrodes (78.1 +/- 4.4 ohms vs 54.6 +/- 2.7 ohms P < .0008), resulting in lower peak current flow through "pediatric" electrode paddles (6.2 +/- 0.5 amps vs 8.7 +/- 0.5 amps P < .002). There was no correlation between joules/kg and peak current flow (r = .26, P > .05).

CONCLUSION

Use of "pediatric" electrode paddles results in higher transthoracic impedance and thus lower peak current flow. In pediatric defibrillation, larger "adult" electrode paddles should be used as soon as chest size permits (approximately 10 kg). Lower transthoracic impedance results in higher current flow that facilitates cardioversion and defibrillation.

Differential growth of neonatal WKY and SHR ventricular myocytes within sympathetic co-cultures

Sympathetic innervation is known to increase heart size in the immature animal, yet the mechanism for this growth remains to be established. This comparative study stereologically quantified the volume of cultured neonatal ventricular myocytes with and without in vitro sympathetic innervation to isolate the mechanisms regulating cardiac growth. Since ventricular myocyte size at birth differs between the spontaneously hypertensive rat (SHR) and the normotensive Wistar-Kyoto (WKY), we questioned whether SHR myocytes respond differently than WKY myocytes to innervation. Four groups of ventricular myocytes from each strain were compared: myocytes grown alone, myocytes innervated by cultured sympathetic neurons, innervated myocytes exposed to adrenoceptor blockade, and non-innervated myocytes in co-culture dishes. Volumes for the myocyte, nucleus, cytoplasm, mitochondria, sarcomeres and other cellular organelles were assessed within each population and between populations. Relative volumes were determined for the mitochondria, sarcomeres, and other cellular components within the cytoplasm. Innervated WKY myocytes were 38% larger than control myocytes (P < 0.0004). This growth was not blocked by adrenoceptor blockade (P = 0.89 vs. innervated) and was present in the non-innervated myocytes distant from the neurons in the co-cultures (P = 0.39 vs. innervated). SHR myocytes were 36% larger than WKY myocytes (P < 0.009) but did not increase with innervation (P = 0.48). SHR myocyte size was also unaffected by adrenoceptor blockade (P = 0.39) or presence of the neurons in the culture dish (P = 0.53). Neonatal WKY ventricular myocyte growth can be provoked in vitro by sympathetic innervation via regulatory mechanisms independent of neuroeffector transmission or anatomic contact, whereas volume of neonatal SHR myocytes is unaltered by sympathetic coculture. These findings are significant for understanding normal as well as aberrant cardiomyocyte growth.

Application of stereological analysis of cell volume to isolated myocytes in culture with and without adrenergic innervation

A three-dimensional analysis to evaluate structural changes in cultured cardiac myocytes following adrenergic innervation was performed using stereological techniques formerly limited to cells in tissue and organs. Cell volumes were calculated for two groups of cells at 96 hours in culture: isolated myocytes and myocytes innervated with adrenergic neurons. Relative and absolute volumes of the nucleus, cytoplasm, and cell were quantified by systematically sampling sections throughout the cell and by point count sampling techniques. Volumetric estimates were similarly determined for the mitochondria, sarcomeres, and other cellular components in the cytoplasm. Data were analyzed with ANOVA and randomized block design to control for variation among the cultures. Adrenergic innervation produced a 44% increase in cell volume, X +/- SEM, (3,344 +/- 196 microns3 to 4,816 +/- 400 microns3, P = 0.007). The absolute volume of mitochondria significantly increased after innervation (521 +/- 42 microns3 to 744 +/- 54 microns3, P less than 0.01). Absolute sarcomere volume did not change significantly (750 +/- 92 microns3 to 642 +/- 1061 microns3, P = 0.14). Other cellular components, defined as all cytoplasmic components except mitochondria and sarcomeres, significantly increased with innervation (1,739 +/- 166 microns3 to 3,097 +/- 338 microns3, P = 0.02). The relative volume of the nucleus and the cytoplasm in the cell remained unchanged following innervation. However, the relative volume of mitochondria decreased by 6%, the percent of the cytoplasm occupied by the sarcomeres decreased by 44%, and the volume occupied by the other cellular components increased by 22%. These findings support the use of stereological analysis as a means to quantify cell volumes of cultured myocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

Chronotropic responsiveness of developing sinoatrial and ventricular rat myocytes to autonomic agonists following adrenergic and cholinergic innervation in vitro

The chronotropic responses of isolated sinoatrial node and ventricular muscle cells to neurotransmitters were compared in vitro with and without selective adrenergic and cholinergic innervation. Explants of either thoracolumbar sympathetic ganglion or sacrococcygeal spinal cord were added to cultures of newborn rat sinus node regions or ventricular apexes harvested before the onset of autonomic innervation in vivo. Catecholamine synthesis was detected by glyoxylic acid histofluorescence. Acetylcholine synthesis was indicated by monoclonal antibody labeling of choline acetyltransferase. After electrical or pharmacological stimulation of neurons, the chronotropic response of individual myocardial cells confirmed the presence of neuroeffector transmission; the nature of the myocyte response identified the stimulated neuron as either adrenergic or cholinergic. Chronotropic responses of all myocardial cells to norepinephrine or acetylcholine were transcribed on a recorder coupled to a video photoconductive cell monitor. Isolated sinoatrial node cells were supersensitive to norepinephrine and acetylcholine; thresholds were 3 x 10(-16) M and 6 x 10(-15) M, respectively. These sinoatrial node cells remained sensitive to both norepinephrine and acetylcholine after the development of innervation in vitro. Ventricular cells also were sensitive with thresholds of 3 x 10(-11) M and 6 x 10(-14) M to norepinephrine and acetylcholine, respectively. However, following in vitro innervation, ventricular cells were significantly less sensitive to norepinephrine and acetylcholine (thresholds 3 x 10(-9) M and 6 x 10(-11) M). These data are the first to demonstrate that neurotrophic modulation is not homogeneous throughout the myocardium and that it may be dependent on the specific myocardial cell innervated.

Pediatric defibrillation: importance of paddle size in determining transthoracic impedance

Transthoracic impedance is a major determinant of successful defibrillation or cardioversion, but no data are available concerning the range and determinants of transthoracic impedance in children. Transthoracic impedance was measured in ten ambulatory infants, 6 weeks to 9 months of age, and 37 children, 1.5 to 15 years of age, using a previously validated "test pulse" technique that measures transthoracic impedance without actually delivering a shock. We used hand-held "pediatric" (21 cm2) and "adult" (83 cm2) electrode paddles coated with either Redux paste or Redux creme. Transthoracic impedance in children was 108 +/- 24 omega (range 61 to 212 omega) using pediatric paddles. Using adult paddles lowered the transthoracic resistance by 47% to 57 +/- 11 omega (range 29 to 101 omega), P less than .05. In infants, transthoracic impedance (measured only with pediatric paddles) was 94 +/- 17 omega (range 74 to 124 omega). Using Redux paste as the coupling agent reduced transthoracic impedance by 13% (P less than .05). Transthoracic impedance was significantly but poorly related to body weight and body surface areas, but the correlations were not sufficiently high to be clinically useful. These data indicate that the larger adult electrode paddles will minimize transthoracic impedance and should be used when the child's thorax is large enough to permit electrode to chest contact over the entire paddle surface. This transition occurred at an approximate weight of 10 kg.

Correlation between directly measured and indirectly estimated sinoatrial conduction time in children

The indirectly estimated sinoatrial conduction time has been widely used in children to assess sinus node (SN) function, but has never been validated in pediatric patients. Using a standard quadripolar catheter with high amplification and low-pass filters, SN electrograms were recorded in 11 of 26 (42%) pediatric cardiac patients (age range 10 months to 18 years) with normal SN function. The sinoatrial conduction time was measured directly from the SN electrogram and estimated indirectly by the premature stimulation and continuous pacing methods. The direct sinoatrial conduction time (15 to 91 ms) in these 11 patients (ages 1 to 18 years) correlated well with that estimated by the premature stimulation method (r = 0.81, n = 9, p less than 0.01). There was a poor correlation between the direct and continuous pacing methods (r = 0.53, n = 8, p = 0.17). It was concluded that SN electrograms can be recorded in children and that there is a good correlation between the directly measured sinoatrial conduction time and the indirectly estimated sinoatrial conduction time by the premature stimulation method.

Concealed atrial parasystole following the Senning operation

A patient with sick sinus syndrome following the Senning operation was also found to have concealed atrial parasystole during intracardiac electrophysiological study. This atrial parasystolic pattern could be converted to atrial bigeminy by changing the atrial drive rate.

Cine computed tomography for diagnosis of superior vena cava obstruction following the Mustard operation

Superior vena caval obstruction is a well described complication following Mustard's repair for transposition of the great arteries. We report a case of a 6-year-old child with superior vena cava obstruction correctly diagnosed by Cine-CT. The advantages of imaging with Cine-CT for this complication are discussed.

Pacemaker management for acute onset of heart block in childhood

Four children aged 2 to 15 years are described who had Stokes-Adams syndrome as the primary cardiac manifestation of complete heart block. All had mild, nonspecific antecedent symptoms without signs of congestive heart failure. Viral neutralizing antibody titers (coxsackievirus B1 and B2) rose significantly in two patients. Electrocardiography demonstrated complete heart block associated with one or more of the following: right bundle branch block, left anterior hemiblock, left bundle branch block, intraventricular conduction delay, and ventricular standstill. In addition, second-degree heart block was seen during the initial or resolving phases of illness. To prevent further life-threatening episodes of Stokes-Adams syndrome, temporary transvenous pacemakers were placed. Two patients with persisting complete heart block required permanent pacemakers. At last examination, the remaining two patients had sinus rhythm and normal conduction. Nonsurgical acquired complete heart block is unusual in childhood, and may be the only manifestation of myocarditis. Extreme bradycardia, which causes syncope, requires immediate temporary cardiac pacing; if the bradycardia persists, a permanent pacemaker should be implanted.

The isolated sinoatrial node cell in primary culture from the newborn rat

We prepared primary cell cultures of the sinus node region from newborn rat hearts. Sinoatrial node cells were easily distinguished from the other cardiac muscle cells and nonmuscle cells in culture by size, configuration, and rapid, attenuated spontaneous contractions (185.0 +/- 8/min, mean +/- SEM). The spontaneously contracting sinoatrial node cells were extremely sensitive to acetylcholine and norepinephrine, responding to concentrations at least 1000-fold less than other cardiac muscle cells. These same sinoatrial node cells in culture were fixed and precisely relocated by either subsequent scanning or transmission electron microscopy. The ultrastructural features of these sinoatrial node cells in culture were similar to those observed in the cells of intact sinus node sections from the source hearts. This study is the first to present single, spontaneously active, neonatal sinoatrial node cells maintained in vitro with morphological and functional properties desirable for physiological investigations.

In vitro adrenergic and cholinergic innervation of the developing rat myocyte

We studied the development of selective adrenergic and cholinergic neuroeffector transmission in primary cultures of isolated ventricular muscle cells. Explants of either thoracolumbar sympathetic ganglia or sacrococcygeal spinal cord were added to newborn rat ventricular cultures harvested prior to the onset of in vivo autonomic innervation. Neuronal growth, migration, and the formation of neuromuscular junctions were observed with light and scanning electron microscopy. Glyoxylic acid histofluorescence, reflecting catecholamine synthesis, was found in only the sympathetic neuromuscular cultures. Choline acetyltransferase activity was detected in both spinal cord and sympathetic neuromuscular cultures, but was significantly higher in the spinal cord neuromuscular cultures. The isolated ventricular muscle cells remained at a constant spontaneous contraction frequency, regardless of the type of culture preparation. Guanethidine sulfate application produced a positive chronotropic response, blocked by propranolol, in the sympathetic neuromuscular cultures, but not in the spinal cord neuromuscular cultures. Bethanechol sulfate produced a negative chronotropic response, blocked by atropine, in the spinal cord neuromuscular cultures, but not in the sympathetic neuromuscular cultures. Isolated ventricular muscle cells in the absence of neurons failed to respond to either agent. Direct microelectrode stimulation of adrenergic or cholinergic neurons likewise respectively produced either a positive or negative ventricular muscle cell chronotropic response. These studies are the first to establish the selective production of functional cholinergic and adrenergic innervation of isolated cardiac muscle cells in vitro.

Foramen ovale/atrial septum area ratio: a marker of transatrial blood flow

We examined 51 cardiac specimens to test the hypothesis that the size of the foramen ovale is directly proportional to the relative volume of transatrial blood flow during cardiac morphogenesis. Included in the study were 18 normal specimens, five with tricuspid atresia, four with pulmonary atresia and intact ventricular septum, nine with secundum atrial septal defect, eight with simple coarctation of the aorta and seven with aortic stenosis. The areas of the foramen ovale and atrial septum were measured and the ratio of foramen ovale to atrial septum was calculated. The area of the atrial septum did not differ significantly among the six groups. Normal specimens had a ratio of 0.19 +/- 0.07. Specimens with tricuspid atresia and pulmonary atresia had ratios of 0.43 +/- 0.01 and 0.38 +/- 0.10, respectively (p less than 0.05). The ratio in specimens with coarctation of the aorta was 0.15 +/- 0.07 (NS). Specimens with aortic stenosis had a ratio of 0.11 +/- 0.06 (p less than 0.05). Specimens with secundum atrial septal defects had a ratio of 0.37 +/- 0.08 (p less than 0.05). These data indicate that the foramen ovale is a marker of transatrial blood flow in utero. Secundum atrial septal defects may be a consequence of increased transatrial blood flow.