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PubMed1980

Supernormal conduction in the canine bundle of His and proximal bundle branches.

We used close bipolar intramural electrodes and catheter electrodes to study the characteristics of conduction in the bundle of His and proximal bundle branches during premature atrial beats in 17 open-chest anesthetized dogs. The electrophysiological properties of the proximal conducting system were heterogenous. The shortest interval between a normal His bundle response and a premature response that was not accompanied by changes in conduction time (the total recovery time) was 258.8 +/- 23.9 (SD) ms for the proximal His and 310.7 +/- 30.6 ms for the distal His and proximal bundle branches. A period of supernormal conduction, in which the conduction times of premature beats were faster than during earlier or later beats, was localized to the distal portion of the bundle of His and proximal bundle branches. The minimal conduction time during the supernormal period was decreased by 9.6 +/- 4.6% below control diastolic conduction times, and the supernormal period was 61.0 +/- 25.7 ms in duration. The characteristics of the period of supernormal conduction in the distal bundle of His and proximal bundle branches were very similar to those previously found in the peripheral bundle branch-Purkinje system. The mechanism of supernormal conduction in the bundle of His is most probably due to a period of supernormal excitability.

Animals↗
PubMed1991

F-actin bundling protein from Physarum polycephalum: purification and its capacity for co-bundling of actin filaments and microtubules.

An F-actin bundling protein was isolated and purified from plasmodium of Physarum polycephalum. The F-actin bundling protein in Physarum extract was passed through a DEAE-cellulose column. After the protein in the fraction was treated with 6 M urea, it was purified by gel filtration on Sephacryl S-300 HR followed by chromatography on CM-Toyopearl (cation exchange) in the presence of 6 M urea. The purified protein gave a single band on SDS-PAGE, and the molecular weight was estimated to be 52,000. This F-actin bundling protein is referred to as the 52 kDa protein. Interestingly, the 52 kDa protein also induced bundling of microtubules. The formation of F-actin and microtubule bundles was Ca(2+)-insensitive, but depended on the salt concentration. Each bundle formed at NaCl concentrations less than 0.1 M. The 52 kDa protein cross-reacted with monoclonal antibody raised against a HeLa 55 kDa protein (an F-actin bundling protein from HeLa cells) (Yamashiro-Matsumura and Matsumura: J. Biol. Chem. 260:5087-5097, 1985). When the 52 kDa protein was added to a mixture of actin filaments and microtubules, co-bundles composed of both filaments formed. This is the first reported example in which an F-actin bundling protein induced co-bundling of actin filaments and microtubules.

Actins↗
PubMed1995

F actin bundles in Drosophila bristles. I. Two filament cross-links are involved in bundling.

Transverse sections though Drosophila bristles reveal 7-11 nearly round, plasma membrane-associated bundles of actin filaments. These filaments are hexagonally packed and in a longitudinal section they show a 12-nm periodicity in both the 1.1 and 1.0 views. From earlier studies this periodicity is attributable to cross-links and indicates that the filaments are maximally cross-linked, singed mutants also have 7-11 bundles, but the bundles are smaller, flattened, and the filaments within the bundles are randomly packed (not hexagonal); no periodicity can be detected in longitudinal sections. Another mutant, forked (f36a), also has 7-11 bundles but even though the bundles are very small, the filaments within them are hexagonally packed and display a 12-nm periodicity in longitudinal section. The singed-forked double mutant lacks filament bundles. Thus there are at least two species of cross-links between adjacent actin filaments. Hints of why two species of cross-links are necessary can be gleaned by studying bristle formation. Bristles sprout with only microtubules within them. A little later in development actin filaments appear. At early stages the filaments in the bundles are randomly packed. Later the filaments in the bundles become hexagonally packed and maximally cross-linked. We consider that the forked proteins may be necessary early in development to tie the filaments together in a bundle so that they can be subsequently zippered together by fascin (the singed gene product).

Actins↗
PubMed1999

Transformation of the collateral vascular bundles into amphivasal vascular bundles in an Arabidopsis mutant.

Arabidopsis inflorescence stems develop a vascular pattern similar to that found in most dicots. The arrangement of vascular tissues within the bundle is collateral, and vascular bundles in the stele are arranged in a ring. Although auxin has been shown to be an inducer of vascular differentiation, little is known about the molecular mechanisms controlling vascular pattern formation. By screening ethyl methanesufonate-mutagenized populations of Arabidopsis, we have isolated an avb1 (amphivasal vascular bundle) mutant with a novel vascular pattern. Unlike the collateral vascular bundles seen in the wild-type stems, the vascular bundles in the avb1 stems were similar to amphivasal bundles, i.e. the xylem completely surrounded the phloem. Furthermore, branching vascular bundles in the avb1 stems abnormally penetrated into the pith, which resulted in a disruption in the ring-like arrangement of vascular bundles in the stele. The avb1 mutation did not affect leaf venation pattern and root vascular organization. Auxin polar transport assay indicated that the avb1 mutation did not disrupt the auxin polar transport activity in inflorescence stems. The avb1 mutation also exhibited pleiotropic phenotypes, including curled stems and extra cauline branches. Genetic analysis indicated that the avb1 mutation was monogenic and partially dominant. The avb1 locus was mapped to a region between markers mi69 and ASB2, which is covered by a yeast artificial chromosome clone, CIC9E2, on chromosome 5. Isolation of the avb1 mutant provides a novel means to study the evolutionary mechanisms controlling the arrangement of vascular tissues within the bundle, as well as the mechanisms controlling the arrangement of vascular bundles in the stele.

Arabidopsis↗
PubMed1984

Functional bundle branch block: discordant response of right and left bundle branches to changes in heart rate.

Faster heart rates shorten refractoriness more in some tissues than in others. This study investigates whether faster heart rates shorten relative refractoriness more in the right than left bundle branch in humans. Premature atrial stimulation at 2 or more basic cycle lengths was performed in 314 patients with no evidence of atrioventricular conduction system disease. In 10 patients, both functional right and left bundle branch block (BBB) developed with premature atrial stimulation. Functional right BBB occurred at the longer basic cycle length, and functional left BBB at the shorter cycle length in 8 patients. In 2 patients functional right and functional left BBB were present at the same cycle length, but functional left BBB occurred at a shorter premature atrial coupling interval. For all patients, the mean functional right bundle branch relative refractoriness was 438 ms at a basic cycle length of 847 ms, and functional left bundle branch relative refractoriness was 357 ms at a cycle length of 622 ms (p less than 0.01). The HV interval was 45 +/- 15 ms at control and increased with functional left BBB to 77 +/- 19 ms (p less than 0.01), but not with functional right BBB. Thus, relative refractoriness of the right and left bundle branches are rate-dependent and discordant. At longer cycle lengths, relative refractoriness of the right bundle branch is greater than that of the left bundle branch, and at shorter cycle lengths relative refractoriness of the left bundle branch is greater than that of the right bundle branch. The relative refractory period curves "cross over" and can explain the presence of both functional right and left BBB in the same patient.

Adolescent↗
PubMed1977

Atypical 2nd degree AV block due to bilateral bundle branch block with Wenckebach phenomenon and concealed conduction in the bundle branch system.

A case of bilateral bundle branch block is described with the following features: -- 2nd degree infranodal AV block due to bilateral, intermittently synchronous "phase 3" bundle branch block; -- occasional AV conduction failure due to concealed His bundle extrasystoles; -- right bundle branch block pattern due to retrograde activation from the left bundle branch; -- QRS complexes having normal duration due to uniform slow conduction in both bundle branches; -- Wenckebach phenomenon in the right bundle branch; -- concealed conduction in both branches. The above interpretations are based on the use of His bundle recordings, results of right atrial stimulation and of pharmacological testing. Determinations of the lengths of all H--H intervals, whether H was followed by a ventricular response or blocked, permitted insight into the mechanism of 2nd degree AV block with varying (right and left) bundle branch block.

Aged↗
PubMed1988

Transcatheter electrical ablation of right bundle branch. A method of treating macroreentrant ventricular tachycardia attributed to bundle branch reentry.

The present study describes the clinical and electrophysiological characteristics of sustained bundle branch reentrant ventricular tachycardia treated with electrical ablation of the right bundle branch. Seven patients presented with syncopal episodes, and six of the seven had documented episodes of ventricular tachycardia. All patients had depressed left ventricular ejection fraction with cardiomegaly. Six of the seven had dilated cardiomyopathy in the absence of significant coronary disease. Twelve-lead electrocardiograms in all seven patients during sinus rhythm were remarkably similar; six demonstrated intraventricular conduction defect resembling left bundle branch block, and one showed left anterior fascicular block. All patients showed prolonged His-to-ventricle intervals during sinus rhythm. Sustained ventricular tachycardia (with atrioventricular dissociation) because of bundle branch reentry was induced in all patients during baseline electrophysiological study. The His-to-ventricle intervals during tachycardia were similar to those seen during sinus rhythm. Electrical ablation of the right bundle branch was accomplished in each patient with delivery of two electrical shocks (170-310 J) through electrode catheters. Right bundle branch block developed on their surface electrocardiogram immediately after the ablation. Follow-up electrophysiological studies showed no inducible ventricular tachycardia. Clinical follow-up showed no recurrence of syncope or ventricular tachycardia. From the data presented, the following can be concluded. First, right bundle branch ablation is a safe and promising means of treating ventricular tachycardia because of bundle branch reentry and can obviate the need for antiarrhythmic drug therapy and its frequent undesirable side effects. Second, there are common clinical and electrophysiological characteristics that are frequently seen in patients with this tachycardia, and the recognition of these common characteristics should alert the physician to a bundle branch reentrant mechanism of ventricular tachycardia.

Aged↗
PubMed2004

Correlation of expression of the actin filament-bundling protein espin with stereociliary bundle formation in the developing inner ear.

The vertebrate hair cell is named for its stereociliary bundle or hair bundle that protrudes from the cell's apical surface. Hair bundles mediate mechanosensitivity, and their highly organized structure plays a critical role in mechanoelectrical transduction and amplification. The prototypical hair bundle is composed of individual stereocilia, 50-300 in number, depending on the animal species and on the type of hair cell. The assembly of stereocilia, in particular, the formation during development of individual rows of stereocilia with descending length, has been analyzed in great morphological detail. Electron microscopic studies have demonstrated that stereocilia are filled with actin filaments that are rigidly cross-linked. The growth of individual rows of stereocilia is associated with the addition of actin filaments and with progressively increasing numbers of cross-bridges between actin filaments. Recently, a mutation in the actin filament-bundling protein espin has been shown to underlie hair bundle degeneration in the deaf jerker mouse, subsequently leading to deafness. Our study was undertaken to investigate the appearance and developmental expression of espin in chicken inner ear sensory epithelia. We found that the onset of espin expression correlates with the initiation and growth of stereocilia bundles in vestibular and cochlear hair cells. Intense espin immunolabeling of stereocilia was colocalized with actin filament staining in all types of hair cells at all developmental stages and in adult animals. Our analysis of espin as a molecular marker for actin filament cross-links in stereocilia is in full accordance with previous morphological studies and implicates espin as an important structural component of hair bundles from initiation of bundle assembly to mature chicken hair cells.

Actin Cytoskeleton↗
PubMed2006

Anisotropic nucleation growth of actin bundle: a model for determining the well-defined thickness of bundles.

Biopolymers such as DNA, F-actins, and microtubules, which are highly charged, rodlike polyelectrolytes, are assembled into architectures with defined morphology and size by electrostatic interaction with multivalent cations (or polycations) in vivo and in vitro. The physical origin to determine their morphology and size is not clearly understood yet. Our results show that the actin bundle formation consists of two stages: the thickness of actin bundles is determined nearly at the initial stage, while the length of actin bundles is determined later on. It is also found that the thickness of actin bundles decreases with the increase of polycation-mediated attraction between F-actins. From these results, we propose the anisotropic nucleation-growth mechanism, in which the thickness of actin bundles is determined by critical nucleus size, whereas the length of actin bundles is determined by the concentration of free actins relative to nucleus concentration. Observing that polycations are concentrated in some sites of actin bundles, which are thought to be nucleation sites to initiate the formation of actin bundles, supports this model. This anisotropic nucleation-growth mechanism of actin bundles can be broadly applied to the self-assembly of rodlike polyelectrolytes.

Actins↗
PubMed2000

Evidence that the transition of HIV-1 gp41 into a six-helix bundle, not the bundle configuration, induces membrane fusion.

Many viral fusion proteins exhibit a six-helix bundle as a core structure. HIV Env-induced fusion was studied to resolve whether membrane merger was due to the transition into the bundle configuration or occurred after bundle formation. Suboptimal temperature was used to arrest fusion at an intermediate stage. When bundle formation was prevented by adding inhibitory peptides at this stage, membranes did not merge upon raising temperature. Inversely, when membrane merger was prevented by incorporating lysophosphatidylcholine (LPC) into cell membranes at the intermediate, the bundle did not form upon optimizing temperature. In the absence of LPC, the six-helix bundle did not form when the temperature of the intermediate was raised for times too short to promote fusion. Kinetic measures showed that after the temperature pulse, cells had not advanced further toward fusion. The latter results indicate that bundle formation is the rate-limiting step between the arrested intermediate and fusion. Electrical measures showed that the HIV Env-induced pore is initially large and grows rapidly. It is proposed that bundle formation and fusion are each contingent on the other and that movement of Env during its transition into the six-helix bundle directly induces the lipid rearrangements of membrane fusion. Because peptide inhibition showed that, at the intermediate stage, the heptad repeats of gp41 have become stably exposed, creation of the intermediate could be of importance in drug and/or vaccine development.

CD4-Positive T-Lymphocytes↗
PubMed1985

Surgical anatomy of the atrioventricular conduction bundle in anomalous muscle bundle of the right ventricle with subarterial ventricular septal defect.

A stillborn baby girl was found to have an anomalous muscle bundle of the right ventricle, associated with a doubly committed subarterial ventricular septal defect. The latter was separated from the area of the atrioventricular conduction bundle by muscle. Serial histologic sectioning of the specialized atrioventricular junctional area revealed that the final bifurcation of the branching bundle came astride the septum in the inferior angle of the defect. The right bundle branch bifurcated and one of its branches continued along the anomalous muscle bundle in subendocardial position. This anatomy supports the concept that the bundle, in this heart, represented an early takeoff of the moderator band. The surgical anatomy suggests that resection of the anomalous muscle bundle and closure of the ventricular septal defect might well have produced heart block. The generally accepted rule that resection of anomalous muscle bundles in the right ventricle is surgically safe should be reconsidered.

Bundle of His↗
PubMed1978

Reentry within the His-Purkinje system. Elucidation of reentrant circuit using right bundle branch and His bundle recordings.

Routes of impulse propagation during reentry in the His-Purkinje system (Re-HPS) in 13 patients were studied using the right ventricular extra stimulus (V2) method and right bundle branch (RBB) recordings in addition to the conventional His (H) bundle recordings. The H-V and RB-V intervals during sinus rhythm averaged 44.2 and 27.6 msec respectively, with the average antegrade H-RB interval 16.6 msec. All 13 patients demonstrated Re-HPS in the form of V3 showing a left bundle branch block (LBBB) pattern, and two of the 13 patients also manifested V3 with a right bundle branch block (RBBB) pattern. During Re-HPS showing a LBBB pattern, the retrograde activation of the His bundle (H2) in response to V2 occurred via the left bundle branch (LBB), as indicated by inscription of retrograde H2 prior to RB2 in nine of 13 cases (average H2-RB2 = 9.4 msec), and simultaneous incription of retrograde H2 and RB2 in the remaining four. When V3 showed a RBBB pattern the retrograde RB2 preceded H2, suggesting H2 activation via the RBB. These findings suggest that circuit of Re-HPS incorporates both bundle branches and the bundle of His. The H-RB recordings were also useful in distinguishing sustained Re-HPS from atrioventricular nodal reentry when in both instances the QRS complex showed a LBBB pattern.

Adult↗
PubMedDate not supplied

Magnetic stimulation of axons in a nerve bundle: effects of current redistribution in the bundle.

Recently, we developed a model of magnetic stimulation of a concentric axon in an anisotropic nerve bundle. In that earlier paper, we considered a single axon surrounded by a nerve bundle represented as a homogeneous anisotropic monodomain medium. In this paper we extend our previous calculations to examine excitation of axons within a nerve bundle without neglecting the presence of other axons in the nerve bundle. A three-dimensional axial symmetry volume conductor model is used to determine the transmembrane potential response along an axon due to induced electric fields produced by a toroidal coil. Our principal objective is to examine the effect of current redistribution to other axons in the bundle on excitation characteristics. We derive the transmembrane potential along an axon for two currently available models of current redistribution: the biodomain model and the spatial--frequency monodomain model. Results indicate that a reduction in the transmembrane potential along an axon due to the presence of other nerve fibers in the bundle is observed. Axons located at the periphery of a nerve bundle have lower thresholds and different excitation sites compared with axons located near the center of a nerve bundle.

Axons↗
PubMed1982

Partial reconstruction of the microvillus core bundle: characterization of villin as a Ca++-dependent, actin-bundling/depolymerizing protein.

The brush border, isolated from chicken intestine epithelial cells, contains the 95,000 relative molecular mass (M(r)) polypeptide, villin. This report describes the purification and characterization of villin as a Ca(++)-dependent, actin bundling/depolymerizing protein. Then 100,000 g supernatant from a Ca(++) extract of isolated brush borders is composed of three polypeptides of 95,000 (villin), 68,000 (fimbrin), and 42,000 M(r) (actin). Villin, following purification from this extract by differential ammonium sulfate precipitation and ion-exchange chromatography, was mixed with skeletal muscle F-actin. Electron microscopy of negatively stained preparations of these villin-actin mixtures showed that filament bundles were present. This viscosity, sedimentability, and ultrastructural morphology of filament bundles are dependent on the villin:actin molar ratio, the pH, and the free Ca(++) concentration in solution. At low free Ca(++) (less than 10(-6) M), the amount of protein in bundles, when measured by sedimentation, increased as the villin: actin molar ratio increased and reached a plateau at approximately a 4:10 ratio. This behavior correlates with the conversion of single actin filaments into filament bundles as detected in the electron microscope. At high free Ca(++) (more than 10(-6) M), there was a decrease in the apparent viscosity in the villin-actin mixtures to a level measured for the buffer. Furthermore, these Ca(++) effects were correlated with the loss of protein sedimented, the disappearance of filament bundles, and the appearance of short fragments of filaments. Bundle formation is also pH-sensitive, being favored at mildly acidic pH. A decrease in the pH from 7.6 to 6.6 results in an increase in sedimentable protein and also a transformation of loosly associated actin filaments into compact actin bundles. These results are consistent with the suggestions that villin is a bundling protein in the microvillus and is responsible for the Ca(++)-sensitive disassembly of the microvillar cytoskeleton. Thus villin may function in the cytoplasm as a major cytoskeletal element regulating microvillar shape.

Actins↗
PubMed1996

bundle sheath defective2, a Mutation That Disrupts the Coordinated Development of Bundle Sheath and Mesophyll Cells in the Maize Leaf.

Within the maize leaf primordium, coordinated cell division and differentiation patterns result in the development of two morphologically and biochemically distinct photosynthetic cell types, the bundle sheath and the mesophyll. The bundle sheath defective2-mutable1 (bsd2-m1) mutation specifically disrupts C4 differentiation in bundle sheath cells in that the levels of bundle sheath cell-specific photosynthetic enzymes are reduced and the bundle sheath chloroplast structure is aberrant. In contrast, mesophyll cell-specific enzymes accumulate to normal levels, and the mesophyll cell chloroplast structure is not perturbed. Throughout mutant leaf development, the large and small subunits of ribulose bisphosphate carboxylase are absent; however, both rbcL and RbcS transcripts accumulate. Moreover, chloroplast-encoded rbcL transcripts accumulate ectopically in mesophyll cells. Although the bundle sheath cell chloroplast structure deteriorates rapidly when plants are exposed to light, this deterioration is most likely a secondary effect resulting from cell-specific photooxidative damage. Therefore, we propose that the Bsd2 gene plays a direct role in the post-transcriptional control of rbcL transcript accumulation and/or translation, both in bundle sheath and mesophyll cells, and an indirect role in the maintenance of bundle sheath cell chloroplast structure.

Journal Article↗
PubMed2006

Single-bundle versus double-bundle posterior cruciate ligament reconstruction: scientific rationale and surgical technique.

Despite many recent advances in the understanding of the posterior cruciate ligament (PCL) and its function, the optimal treatment of PCL injuries remains controversial. Although it now is well known that the PCL is made up of two distinct bundles, each of which plays a vital role in achieving knee stability, questions abound regarding the need for double-bundle reconstruction rather than single-bundle techniques. Currently, the reconstruction technique is selected based on the injury pattern. In acute (< 3 weeks from the time of injury) combined PCL injuries (PCL/posterolateral corner, PCL/medial collateral ligament, and knee dislocations), a single-bundle reconstruction designed to replicate the anatomy of the anterolateral bundle is used. In acute or chronic PCL injuries in which both the posteromedial bundle of the PCL and the meniscofemoral ligaments remain intact, a single-bundle augmentation is used. A double-bundle reconstruction is performed when all three components of the PCL complex (anterolateral band, posteromedial band, and meniscofemoral ligaments) have been ruptured. These patterns are generally chronic, with severe knee laxity following a previous traumatic injury (PCL/posterolateral corner or knee dislocation). Tailoring the PCL reconstruction technique to the individual injury pattern will likely yield a reconstruction that better replicates the natural biomechanics of the native knee, thereby resulting in better functional outcomes.

Anterior Cruciate Ligament↗