Biomedical subjects
Publications and source records attributed to M R Gold.
Rhythm disturbances can range from the harmless to the life-threatening, and treatment varies accordingly, from watchful waiting to emergency intervention. Traditional antiarrhythmic medications have largely been supplanted by newer agents; pharmacologic therapy is giving way to device-based treatment, including pacemakers, defibrillators, and catheter ablation.
We have previously shown that the B cell Ag receptor (BCR) activates phosphatidylinositol (PI) 3-kinase. We now show that a serine/threonine kinase called Akt or protein kinase B is a downstream target of PI 3-kinase in B cells. Akt has been shown to promote cell survival as well as the transcription and translation of proteins involved in cell cycle progression. Using an Ab that specifically recognizes the activated form of Akt that is phosphorylated on serine 473, we show that BCR engagement activates Akt in a PI 3-kinase-dependent manner. These results were confirmed using in vitro kinase assays. Moreover, BCR ligation also induced phosphorylation of Akt of threonine 308, another modification that is required for activation of Akt. In the DT40 chicken B cell line, phosphorylation of Akt on serine 473 was completely dependent on the Lyn tyrosine kinase, while the Syk tyrosine kinase was required for sustained phosphorylation of Akt. Complementary experiments in BCR-expressing AtT20 endocrine cells confirmed that Src kinases are sufficient for BCR-induced Akt phosphorylation, but that Syk is required for sustained phosphorylation of Akt on both serine 473 and threonine 308. In insulin-responsive cells, Akt phosphorylates and inactivates the serine/threonine kinase glycogen synthase kinase-3 (GSK-3). Inactivation of GSK-3 may promote nuclear accumulation of several transcription factors, including NF-ATc. We found that BCR engagement induced GSK-3 phosphorylation and decreased GSK-3 enzyme activity. Thus, BCR ligation initiates a PI 3-kinase/Akt/GSK-3 signaling pathway.
Protein kinase C (PKC) enzymes have been implicated as key intermediates in B-cell antigen receptor (BCR) signaling. Each of the 11 PKC isoforms may phosphorylate different substrates and regulate different cellular processes. In this report we show that PKC-delta (PKC-delta) is a target of BCR signaling. BCR engagement increased the amount of PKC-delta in the membrane-enriched particulate fraction of B-cells, suggesting that BCR activates PKC-delta. BCR ligation also caused substantial tyrosine phosphorylation of PKC-delta. We show that activation of phospholipase C by BCR is necessary for both PKC-delta membrane localization and tyrosine phosphorylation. In contrast, phorbol esters which mimic the action of diacylglycerol could recruit PKC-delta to cellular membranes but did not induce tyrosine phosphorylation of PKC-delta. These data suggest a model in which phospholipase C-dependent production of diacylglycerol recruits PKC-delta to cellular membranes where it is then phosphorylated by BCR-activated tyrosine kinases.
We have previously shown that CD40 causes strong activation of the c-Jun N-terminal kinase (JNK), the p38 mitogen-activated protein kinases (MAPK) and MAPKAP kinase-2, a downstream target of p38 MAPK. To identify signaling motifs in the CD40 cytoplasmic domain that are responsible for activation of these kinases, we have created a set of 11 chimeric receptors consisting of the extracellular and transmembrane domains of CD8 fused to portions of the murine CD40 cytoplasmic domain. These chimeric receptors were expressed in WEHI-231 B lymphoma cells. We found that amino acids 35-45 of the CD40 cytoplasmic domain constitute an independent signaling motif that is sufficient for activation of the JNK and p38 MAPK pathways, as well as for induction of I kappa B alpha phosphorylation and degradation. Amino acids 35-45 were also sufficient to protect WEHI-231 cells from anti-IgM-induced growth arrest. This is the same region of CD40 required for binding the TNF receptor-associated factor-2 (TRAF2), TRAF3, and TRAF5 adapter proteins. These data support the idea that one or more of these TRAF proteins couple CD40 to the kinase cascades that activate NF-kappa B, JNK, and p38 MAPK.
BACKGROUND: Implantable cardioverter-defibrillator function is critically dependent on reliable sensing of intracardiac signals. Lead systems that use integrated sensing, in which the distal shocking coil is part of both the sensing and shocking pathways, may be prone to undersensing of ventricular fibrillation, especially during redetection after a failed first shock. To assess the effect of endocardial lead system on redetection, we compared a dedicated rate-sensing lead and 2 generations of integrated sensing defibrillator leads with a uniform testing algorithm and pulse generator. METHODS: The study group consisted of 72 patients after implantable cardioverter-defibrillator implantation. Three transvenous rate-sensing leads were evaluated: a standard pacing lead, incorporating true bipolar sensing without ventricular coils, or an integrated shocking and sensing lead (Endotak C) with either 6-mm (60 series) or 12-mm (70 series) spacing between the sensing tip and shocking coil. Redetection was assessed from a failed first shock just below defibrillation threshold. RESULTS: Compared with the dedicated bipolar lead, redetection was prolonged with the 60 series lead (8.3 +/- 3.6 vs 6.6 +/- 2.3 seconds, P =.04). Moreover, prolonged redetection (>8 seconds) was observed in 41% of patients with 60 series leads compared with only 11% with dedicated bipolar leads (P <.01). No significant effects on redetection were noted with an integrated lead with greater spacing between the tip and coil (70 series). CONCLUSIONS: Delayed redetection is frequently noted with an integrated lead with close spacing between the tip and coil. Detailed evaluation of detection and redetection of these leads should be performed at the time of pulse generator replacement.
BACKGROUND: Previous studies have reported varying success rates in overdrive pace termination of atrial flutter. We hypothesized that these discrepancies might be caused by differences in study populations. Accordingly, we prospectively compared the success rate of pacing in patients with atrial flutter that occurred after heart surgery with that of patients with atrial flutter from other causes. METHODS AND RESULTS: The study population consisted of 65 consecutive patients referred for pace termination of typical (type I) atrial flutter. Pacing was performed in 30-second bursts, starting at the flutter cycle length, and repeated in 5-ms decrements until normal sinus rhythm or atrial fibrillation occurred. Normal sinus rhythm was restored in 38 (65%) patients. Of 20 patients whose flutter was precipitated by heart surgery, 19 (95%) were successfully pace terminated. In contrast, pace termination was successful in only 47% of the remainder of the population (P <.001). No other clinical parameters were predictive of outcome. CONCLUSIONS: We conclude that overdrive pacing is an effective means of terminating atrial flutter that has occurred after heart surgery. Alternative methods should be considered as the initial therapeutic approach in patients with atrial flutter from other causes.
OBJECTIVE: This study examined the effect of exercise on markers of fibrinolysis and coagulation in users and nonusers of oral contraceptives. STUDY DESIGN: Fourteen oral contraceptive users and 14 nonusers performed a maximal exercise test on a cycle ergometer. Blood samples were collected before and immediately after the completion of the test. A repeated-measures analysis of variance was used for statistical analysis with values considered significant at P =.05. RESULTS: Acute maximal exercise resulted in significant increases in tissue plasminogen activator activity in both groups. There was a trend toward a smaller increase in tissue plasminogen activator activity in oral contraceptive users, but the difference between groups was not statistically significant. Plasminogen activator inhibitor 1 activity was reduced with exercise in both groups but with a significantly greater decrease observed in the nonusers (P <.0001). Prothrombin fragment 1+2 was significantly higher (P <.0001) in the oral contraceptive group but did not change with exercise. Epinephrine levels before and after exercise were similar between the 2 groups, but postexercise norepinephrine concentrations were significantly lower (P =.026) in the oral contraceptive users. CONCLUSION: These data suggest that oral contraceptive use blunts the fibrinolytic response to exercise. This, together with increased coagulation activation in oral contraceptive users, may alter the hemostatic balance during exercise.
Explore the source record for details and available documents.
OBJECTIVES: The purpose of this study was to compare transvenous atrial defibrillation thresholds with lead configurations consisting of an active left pectoral electrode and either single or dual transvenous coils. BACKGROUND: Low atrial defibrillation thresholds are achieved using complex lead systems including coils in the coronary sinus. However, the efficacy of more simple ventricular defibrillation leads with active pectoral pulse generators to defibrillate atrial fibrillation (AF) is unknown. METHODS: This study was a prospective, randomized assessment of shock configuration on atrial defibrillation thresholds in 32 patients. The lead system was a dual coil Endotak DSP lead with a left pectoral pulse generator emulator. Shocks were delivered either between the right ventricular coil and an active can in common with the proximal atrial coil (triad) or between the atrial coil and active can (transatrial). RESULTS: Delivered energy at defibrillation threshold was 7.1 +/- 6.0 J in the transatrial configuration and 4.0 +/- 4.2 J in the triad configuration (p < 0.005). Moreover, a low threshold (< or = 3 J) was observed in 69% of subjects in the triad configuration but only 47% in the transatrial configuration. Peak voltage and shock impedance were also lowered significantly in the triad configuration. Left atrial size was the only clinical predictor of the defibrillation threshold (r = 0.57, p < 0.002). CONCLUSIONS: These results indicate that low atrial defibrillation thresholds can be achieved using a single-pass transvenous ventricular defibrillation lead with a conventional ventricular defibrillation pathway. These data support the development of the combined atrial and ventricular defibrillator system.
Murine B cell lines such as WEHI-231, BAL17 and M12.4.1 are frequently used as model systems to study signal transduction, cell cycle regulation, and apoptosis. Dissection of these processes often involves expressing exogenous genes in these cells. Electroporation is an inefficient method to express genes in B cell lines and requires several weeks to isolate and analyze clones, followed by an additional one to two weeks to grow sufficient cells for biochemical experiments (e.g. immunoprecipitations). In this report, we describe an optimized procedure for retroviral-mediated gene transfer into murine B cell lines that allows one to obtain a pure population of cells expressing an exogenous gene within 4 days. Two days post-infection, between 10% (BAL17 and M12.4.1 cells) and 70% (WEHI-231 cells) of the cells express the exogenous gene. Culturing the cells for an additional 48 hours with puromycin kills all the non-infected cells and yields a pure population of cells that express the exogenous gene. Sufficient cells for biochemical experiments can be obtained by expanding the cell culture for an additional 5 to 7 days. This rapid and efficient retroviral-mediated gene transfer procedure can greatly expedite the study of signal transduction and other processes in B cells.
Shock impedance is an important determinant of defibrillation efficacy. Lead configuration, shock polarity, and delivered energy can affect shock impedance, but these variables have not been studied in active can lead systems. The present study was a prospective evaluation of 25 patients undergoing initial transvenous defibrillator implantation. In all patients, a dual coil lead and pectoral emulator were placed and three lead configurations were tested in random order: Lead (distal to proximal coil), unipolar (distal coil to can), and triad (distal coil to can + proximal coil). Shock energies of 0.1- to 15-J shock were evaluated. Impedance increased a mean of 21% as delivered energy was decreased (P < 0.001), an effect independent of lead configuration. At all delivered energies, impedances in the unipolar configuration were about 40% higher than triad, while the lead configuration was about 20% higher than triad (ps < 0.001). Polarity did not affect impedance. These results indicate that transvenous lead configurations and delivered energy, but not polarity, significantly influence shock impedance. The magnitude of the increase of impedance at low energies is independent of the shocking pathway. This effect has important implications for low energy shocks used to terminate atrial fibrillation or ventricular tachycardia.
Inappropriate therapies delivered by implantable cardioverter defibrillators (ICDs) for supraventricular arrhythmias remain a common problem, particularly in the event of rapidly conducted atrial fibrillation or marked sinus tachycardia. The ability to differentiate between ventricular tachycardia and supraventricular arrhythmias is the major goal of discrimination algorithms. Therefore, we developed a new algorithm, SimDis, utilizing morphological features of the shocking electrograms. This algorithm was developed from electrogram data obtained from 36 patients undergoing ICD implantation. An independent test set was evaluated in 25 patients. Recordings were made in sinus rhythm, sinus tachycardia, and following the induction of ventricular tachycardia and atrial fibrillation. The arrhythmia complex is defined as wide if the duration is at least 30% greater than the template in sinus rhythm. For narrow complexes, four maximum and minimum values were measured to form a 4-element feature vector, which was compared with a representative feature vector during normal sinus rhythm. For each rhythm, any wide complex was classified as ventricular tachycardia. For narrow complexes, the second step of the algorithm compared the electrogram with the template, computing similarity and dissimilarity values. These values were then mapped to determine if they fell within a previously established discrimination boundary. On the independent test set, the SimDis algorithm correctly classified 100% of ventricular tachycardias (27/27), 98% of sinus tachycardias (54/55), and 100% of episodes of atrial fibrillation (37/37). We conclude that the SimDis algorithm yields high sensitivity (100%) and specificity (99%) for arrhythmia discrimination, using the computational capabilities of an ICD system.
Explore the source record for details and available documents.
We report the case of an electrical storm in a cardiac arrest survivor with an ICD, in whom chronic oral amiodarone failed to suppress ventricular arrhythmias, and in whom intravenous amiodarone resulted in stability for 6 weeks prior to successful cardiac transplantation. Intravenous amiodarone can be successful in suppressing life-threatening ventricular arrhythmias, even when chronic oral amiodarone is unsuccessful.
Nonpenetrating chest trauma has been reported to cause acute and transient disorders of impulse formation and propagation, including intraventricular conduction delay and heart block. We report a case of immediate and sustained complete heart block following blunt chest injury.
INTRODUCTION: The measurement of microvolt level T wave alternans (TWA) is a technique for detecting arrhythmia vulnerability. Previous studies demonstrated that the magnitude of TWA is dependent on heart rate. However, the effects of antiarrhythmic drugs on TWA are unknown. METHODS AND RESULTS: This was a prospective evaluation of intravenous procainamide on TWA in 24 subjects with inducible sustained ventricular tachycardia (VT). Measurements of TWA were performed at baseline in the drug-free state and after procainamide loading (1,204+/-278 mg). Recordings were made in normal sinus rhythm, and during atrial pacing at 100 beats/min and 120 beats/min. The magnitude of TWA in the vector magnitude lead was decreased by procainamide at all heart rates: 0.6+/-0.8 to 0.3+/-0.4 microV in sinus rhythm, 2.0+/-1.6 to 0.7+/-0.7 microV at 100 beats/min, and 3.0+/-2.0 to 1.7+/-1.8 microV at 120 beats/min (P<0.001 by analysis of variance). The sensitivity of TWA for the induction of VT at baseline was 5% in sinus, 60% at 100 beats/min, and 87% at 120 beats/min, while it decreased with procainamide to 5%, 19%, and 60%, respectively. Decreases in TWA in response to procainamide were independent of the antiarrhythmic effects on VT inducibility. CONCLUSIONS: These results indicate that the magnitude of TWA decreases with acute procainamide loading and this effect decreases the sensitivity of TWA for the induction of sustained VT.
Compounds with antiendotoxin properties have been extensively studied for their potential as therapeutic agents for sepsis attributable to gram-negative bacteria. However, with the increasing incidence of gram-positive sepsis, there is interest in identifying compounds with a broad spectrum of action against both gram-positive and gram-negative bacteria. A series of synthetic alpha-helical cationic peptides related to bee melittin and silk moth cecropin have previously been shown to bind lipopolysaccharide (LPS) with high affinity, inhibit LPS-induced tumor necrosis factor alpha (TNF-alpha) production in vitro and in vivo, and kill gram-negative bacteria. In this study, we analyzed whether these peptides were active against gram-positive bacteria; whether they could bind to lipoteichoic acid (LTA), the major proinflammatory structure on gram-positive bacteria; and whether they could block the ability of LTA to promote the release of cytokines by the RAW 264.7 murine macrophage cell line. We found that the cationic peptides demonstrated moderate growth-inhibitory activity toward gram-positive bacteria. In addition, the peptides bound LTA with high affinity. This correlated with the ability of the peptides to block LTA-induced production of TNF and interleukin-6 by RAW 264.7 cells but did not correlate with their ability to kill the bacteria. The peptides also effectively inhibited LTA-induced TNF production in a whole human blood assay. The peptides were also able to partly block the ability of heat-killed Staphylococcus aureus, as well as soluble products of live S. aureus, to stimulate cytokine production by macrophages. Our results indicate that these cationic peptides may be useful to prevent sepsis and inflammation caused by both gram-negative and gram-positive bacteria.
Explore the source record for details and available documents.