Dendritic cell survival and maturation are regulated by different signaling pathways.

Although dendritic cell (DC) activation is a critical event for the induction of immune responses, the signaling pathways involved in this process have not been characterized. In this report, we show that DC activation induced by lipopolysaccharide (LPS) can be separated into two distinct processes: first, maturation, leading to upregulation of MHC and costimulatory molecules, and second, rescue from immediate apoptosis after withdrawal of growth factors (survival). Using a DC culture system that allowed us to propagate immature growth factor-dependent DCs, we have investigated the signaling pathways activated by LPS. We found that LPS induced nuclear translocation of the nuclear factor (NF)-kappaB transcription factor. Inhibition of NF-kappaB activation blocked maturation of DCs in terms of upregulation of major histocompatibility complex and costimulatory molecules. In addition, we found that LPS activated the extracellular signal-regulated kinase (ERK), and that specific inhibition of MEK1, the kinase which activates ERK, abrogated the ability of LPS to prevent apoptosis but did not inhibit DC maturation or NF-kappaB nuclear translocation. These results indicate that ERK and NF-kappaB regulate different aspects of LPS-induced DC activation: ERK regulates DC survival whereas NF-kappaB is responsible for DC maturation.

Modification of the discharge of vagal cardiac neurons during learned heart rate change.

Visually conditioned heart rate change in the pigeon has been developed as a vertebrate model system for the cellular neurophysiological analysis of associative learning. In previous studies of the "final common path," it was shown that both the vagal and sympathetic cardiac innervations contribute to this response. The present experiments indicate that, prior to any behavioral training, the visual stimulus elicits a small decrease in the discharge of vagal cardiac neurons. During conditioning, this stimulus evokes a progressively greater decrease in discharge that parallels the acquisition of the conditioned cardioacceleration. In contrast, nonassociative control animals show habituation of the initial decrease in discharge. These data confirm the involvement of the vagal cardiac innervation in conditioned heart rate change, indicate that the vagal innervation acts synergistically with the sympathetic to produce cardioacceleration, and suggest that a short-latency pathway mediates the conditioned response.

Inhibitory conductance changes at synapses in the lamprey brainstem.

Although the conductance and kinetic behavior of inhibitory synaptic channels have been studied in a number of nerve and muscle cells, there has been little if any detailed study of such channels at synapses in the vertebrate central nervous system or of the relation of such channels to natural synaptic events. In the experiments reported here, current noise measurements were used to obtain such information at synapses on Müller cells in the lamprey brainstem. Application of glycine to the cells activated synaptic channels with large conductances and relaxation time constants (70 picosiemens and 33 milliseconds, respectively, at 3 degrees to 10 degrees C). Spontaneous inhibitory synaptic currents had a mean conductance of 107 nanosiemens and decayed with the same time constant. In addition, the glycine responses and the spontaneous currents had the same reversal potential and both were abolished by strychnine. These results support the idea that glycine is the natural inhibitory transmitter at these synapses and suggest that one quantum of transmitter activates about 1500 elementary conductance channels.

Noninvasive tissue adhesive for cardiac implantable electronic device pocket closure: the TAPE pilot study.

PURPOSE: Device infection is a serious complication of cardiac implantable electronic devices (CIED). Ensuring complete pocket closure can be time consuming, but remains vital to prevent infection. The Zip® Surgical Skin Closure (ZIP) is a noninvasive adhesive device applied to the skin as an alternative to subcuticular sutures for skin closure. We hypothesized that using this device would decrease pocket closure times without increasing the risk of pocket infections. This is a single center, retrospective cohort study to compare pocket closure times and infection rates between ZIP and standard suture for CIED pocket closure. METHODS: Two separate groups of consecutive new intravenous implants, upgrades, and pulse generator replacements from October 2015 to April 2017 were included. A total of 175 patients were included, using either ZIP (n = 80) or suture (n = 95). Total procedure time (local anesthetic to dressing application) and pocket closure time (fascial suture to dressing application) were compared. Pocket infections were defined as infections leading to CIED extraction or wound dehiscence requiring repeat procedure. Statistical analysis was performed using chi square test and Student's t test. RESULTS: Pocket closure time and procedure time were significantly shorter for the ZIP group (14.9 ± 6.8 vs 20.1 ± 11.09 min, p = 0.0003) and (65.02 ± 30.4 vs 83.83 ± 40.3 min, p = 0.0008), respectively. No pocket infections occurred in the Zip group, while the suture group had 2:1 wound dehiscence and 1 pocket infection. CONCLUSION: The ZIP device resulted in significantly shorter pocket closure and procedure times without increasing device pocket infections.

New views of BCR structure and organization.

Recent work has provided new insights into the stoichiometry of BCR subunits, as well as the organization of the BCR before and after engagement by antigen. On resting cells, the BCR may be pre-assembled into oligomeric receptor complexes that generate a basal level of signaling. After antigen binding, the BCR may be organized into larger receptor arrays that reside in lipid rafts - sites where signaling enzymes are concentrated. The critical role of BCR assembly and organization in B cell function is underscored by the recent findings that this process is altered in many B cell tumors.

Biochemistry of B lymphocyte activation.

The activation of B lymphocytes from resting cells proceeds from the events of early activation to clonal proliferation to final differentiation into either an antibody-secreting plasma cell or a memory B cell. This is a complex activation process marked by several alternative pathways, depending on the nature of the initial antigenic stimulus. Over the past 5-10 years, there has been an explosion of studies examining the biochemical nature of various steps in these pathways. Some of that progress is reviewed here. In particular, we have described in detail what is known about the structure and function of the AgR, as this molecule plays a pivotal role in B cell responses of various types. We have also reviewed recent progress in understanding the mechanism of action of contact-dependent T cell help and of the cytokine receptors, particularly the receptors for IL-2, IL-4, and IL-6. Clearly, all of these areas represent active areas of investigation and great progress can be anticipated in the next few years.

Effect of second-phase duration on the strength-duration relation for human transvenous defibrillation.

BACKGROUND: The mechanism by which biphasic waveforms improve defibrillation efficacy is unclear. In addition, the optimal shape of the biphasic waveforms remains controversial. Animal experiments suggest that prolonging the duration of the second phase longer than the first worsens defibrillation thresholds (DFT). The purpose of this study was to determine the strength-duration relation for the second phase of a biphasic defibrillation waveform in humans. METHODS AND RESULTS: This was a prospective, randomized study of biphasic DFT in 36 patients; a uniform dual-coil transvenous lead system was used. In each patient, 3 DFTs were determined with the pulse duration for the second phase of the defibrillation waveform varying between 1 and 18 ms. The duration of the first phase was fixed at 6 ms and the capacitance was 150 microF. There was a significant increase in the leading edge voltage at DFT only when the second-phase pulse duration was decreased to 1 ms. There was no increase in DFT voltage even when the second-phase pulse duration was increased from 2 to 18 ms. Similar relations were observed for stored energy, leading edge current, or phase 2 energy. The normalized average current delivered during phase 2 decreased monotonically with increasing phase 2 duration. CONCLUSIONS: In humans, the biphasic DFT voltage or energy is increased only when the second phase of the waveform is <2 ms. The DFT voltage is insensitive to increasing the second phase of the defibrillator waveform to as long as 18 ms, or 3 times the duration of the first phase of the waveform.

Biphasic waveforms prevent the chronic rise of defibrillation thresholds with a transvenous lead system.

OBJECTIVES: The purpose of this study was to compare chronic changes in monophasic and biphasic defibrillation thresholds using a uniform transvenous lead system and testing protocol. BACKGROUND: Defibrillation thresholds increase over time in patients with nonthoracotomy lead systems. This increase can result in an inadequate chronic defibrillation safety margin and could limit the safety of smaller pulse generators, which have a reduced maximal output. However, previous studies of the temporal changes of defibrillation thresholds evaluated complex lead systems or monophasic shock waveforms, neither of which are used with current technology. METHODS: This study was a prospective, randomized assessment of the effects of shock waveforms on the changes of transvenous defibrillation thresholds over time. Paired monophasic and biphasic thresholds were measured both at implantation and at follow-up (250 +/- 105 days) in 24 consecutive patients who were not receiving antiarrhythmic drugs. The lead system was a dual-coil Endotak C lead, and reverse polarity shocks (distal coil = anode) were delivered. RESULTS: Monophasic defibrillation thresholds increased from (mean +/- SD) 13.7 +/- 6.0 J to 16.8 +/- 6.7 J (p = 0.02), whereas biphasic thresholds were unchanged (10.4 +/- 4.3 J to 10.2 +/- 4.8 J, p = 0.86) in the same patients. Shock impedance chronically increased (47.0 omega to 50.5 omega, p = 0.02) and was unaffected by waveform. CONCLUSIONS: These results indicate that biphasic shocks prevent the chronic increase in defibrillation thresholds with a transvenous lead system.

Dual-chamber pacing with a short atrioventricular delay in congestive heart failure: a randomized study.

OBJECTIVES: This prospective study assessed the initial hemodynamic effects and long-term clinical benefits of dual-chamber pacing with a short atrioventricular (AV) delay in patients with chronic heart failure who had no traditional indication for pacemaker implantation. BACKGROUND: Dual-chamber pacing with a short AV delay has been proposed as a nonpharmacologic treatment for drug-refractory heart failure. Both initial and long-term hemodynamic as well as functional benefits have been reported. All previous studies have used an AV delay of 100 ms. Despite encouraging results, these previous studies have been anecdotal and uncontrolled. METHODS: This double-blind, randomized, crossover trial included 12 subjects with chronic congestive heart failure despite optimal medical therapy. Patients were required to be in sinus rhythm with no evidence of significant bradyarrhythmias. On the day after implantation of a dual-chamber pacemaker, invasive hemodynamic measurements were made at varying AV delays between 100 and 200 ms. Patients were then randomized to either dual-chamber pacing with a 100-ms AV delay or backup mode (VVI at 40 beats/min). After 4 to 6 weeks, crossover to the other pacing mode was programmed. RESULTS: Hemodynamic measurements on the day after pacemaker implantation demonstrated no benefit of pacing with any AV delay compared with intrinsic conduction. At the optimal AV interval for each patient, neither cardiac output (4.5 +/- 1.5 vs 4.7 +/- 1.6 liters/min [mean +/- SD]) nor wedge pressure (16 +/- 10 vs 17 +/- 8 mm Hg) improved significantly from baseline measurements during intrinsic conduction. The long-term pacing protocol was completed in nine patients. Ejection fraction was 16 +/- 6% with dual-chamber (VDD mode) pacing and 18 +/- 4% in backup mode (p = NS). No patient had an increase in ejection fraction by > or = 5% with VDD pacing, nor did any patient improve in New York Heart Association functional class with short AV delay dual-chamber pacing. Also, there were no significant reductions in body weight or diuretic requirements during this pacing period. CONCLUSIONS: Dual-chamber pacing with a short AV delay does not improve hemodynamic and clinical status or ejection fraction measured on the day after pacemaker implantation in patients with chronic congestive heart failure. Routine use of pacemaker therapy with a short AV delay aas a primary treatment of heart failure in patients without standard arrhythmic indications is unwarranted.

Complications associated with pectoral cardioverter-defibrillator implantation: comparison of subcutaneous and submuscular approaches. Worldwide Jewel Investigators.

OBJECTIVES: The aim of this study was to compare complications in a large cohort of patients undergoing pectoral cardioverter-defibrillator implantation with a subcutaneous or submuscular approach. BACKGROUND: Pectoral placement of implantable cardioverter-defibrillator (ICD) pulse generators is now routine because of downsizing of these devices. subcutaneous implantation has been advocated by some because it is a simple surgical procedure comparable to pacemaker insertion. Others have favored submuscular insertion to avoid wound complications. These surgical approaches have not been compared previously. METHODS: The subjects for this study were 1,000 consecutive patients receiving a Medtronic Jewel ICD at 93 centers worldwide. Cumulative follow-up for all patients was 633.7 patient-years, with 64.9% of patients followed up for > or = 6 months. The complications evaluated were erosion, pocket hematoma, seroma, wound infection, dehiscence, device migration, lead fracture and dislodgment. RESULTS: Subcutaneous implantation was performed in 604 patients and submuscular implantation in the remaining 396. The median procedural times were shorter for subcutaneous implantation (p = 0.014). In addition, the cumulative percentage of patients free from erosion was greater for subcutaneous implantations (p = 0.03, 100% vs. 99.1% at 6 months). However, lead dislodgment was more common with subcutaneous implantations (p = 0.019, 2.3% vs. 0.5% at 6 months) and occurred primarily during the first month postoperatively. Overall, there were no significant differences in cumulative freedom from complications between groups (4.1% vs. 2.5%, p = 0.1836). CONCLUSIONS: Subcutaneous pectoral implantation of this ICD can be performed safely and has a low complication rate. This approach requires a simple surgical procedure and, compared with the submuscular approach, is associated with shorter procedure times and comparable overall complication rates. However, early follow-up is important in view of the increased lead dislodgment rate.

Comparison of single- and dual-coil active pectoral defibrillation lead systems.

OBJECTIVES: The purpose of this study was to compare defibrillation thresholds with lead systems consisting of an active left pectoral electrode and either single or dual transvenous coils. BACKGROUND: Lead systems that include an active pectoral pulse generator reduce defibrillation thresholds and permit transvenous defibrillation in nearly all patients. A further improvement in defibrillation efficacy is desirable to allow for smaller pulse generators with a reduced maximal output. METHODS: This prospective study was performed in 50 consecutive patients. Each patient was evaluated with two lead configurations with the order of testing randomized. Shocks were delivered between the right ventricular coil and either an active can alone (single coil) or an active can with the proximal atrial coil (dual coil). The right ventricular coil was the cathode for the first phase of the biphasic defibrillation waveform. RESULTS: Delivered energy at the defibrillation threshold was 10.1+/-5.0 J for the single-coil configuration and 8.7+/-4.0 J for the dual-coil configuration (p < 0.02). Moreover, 98% of patients had low (<15 J) thresholds with the dual-coil lead system, compared with 88% of patients with the single-coil configuration (p=0.05). Leading edge voltage (p < 0.001) and shock impedance (p < 0.001) were also decreased with the dual-coil configuration, although peak current was increased (p < 0.001). CONCLUSIONS: A dual-coil, active pectoral lead system reduces defibrillation energy requirements compared with a single-coil, unipolar configuration.

Atrial defibrillation with a transvenous lead: a randomized comparison of active can shocking pathways.

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.

High dose oral amiodarone loading exerts important hemodynamic actions in patients with congestive heart failure.

OBJECTIVES: The purpose of this study was to use invasive monitoring to analyze the hemodynamic effects of both a large single dose and a 48-h loading regimen of amiodarone in patients with severe heart failure. BACKGROUND: Amiodarone is frequently used as an antiarrhythmic agent in patients with congestive heart failure, but the impact of this agent on cardiac function remains controversial. Recent successful experience with a rapid oral load of amiodarone makes invasive testing of the hemodynamic effects of oral amiodarone in such patients now feasible. METHODS: After baseline hemodynamic assessment (using balloon-tipped pulmonary artery catheters) and electrocardiographic measurements, 16 patients received 12.5 mg/kg body weight of amiodarone orally. Hemodynamic measurements were obtained hourly for 4 h. Patients then received this dose an additional seven times over the next 2 days. Hemodynamic variables and QRS, QT and PR intervals were measured after 48 h of treatment. RESULTS: Vasodilation was seen between 1 and 3 h after drug administration. Systemic vascular resistance decreased 326 +/- 135 dynes.s.cm-5, cardiac index increased 0.24 +/- 0.08 liters/min per m2 and mean arterial pressure decreased 6 +/- 3 mm Hg (mean +/- SEM, all p < 0.05). After 48 h of amiodarone administration, heart rate decreased 23 +/- 3 beats/min (p < 0.005), stroke volume increased 9 +/- 3 ml (p < 0.005), cardiac index decreased 0.23 +/- 0.09 ml/min per m2 (p < 0.05), pulmonary capillary wedge pressure increased 4 +/- 1 mm Hg (p < 0.01), right atrial pressure increased 3 +/- 1 mm Hg (p < 0.005) and QT and PR intervals were markedly prolonged (p < 0.01). CONCLUSIONS: Although the first dose caused vasodilation, a complete loading regimen of amiodarone produced a decreased heart rate with elevated filling pressures and decreased cardiac index.

Temporal decline in defibrillation thresholds with an active pectoral lead system.

OBJECTIVES: The objective of this study was to characterize temporal changes in defibrillation thresholds (DFTs) after implantation with an active pectoral, dual-coil transvenous lead system. BACKGROUND: Ventricular DFTs rise over time when monophasic waveforms are used with non-thoracotomy lead systems. This effect is attenuated when biphasic waveforms are used with transvenous lead systems; however, significant increases in DFT still occur in a minority of patients. The long-term stability of DFTs with contemporary active pectoral lead systems is unknown. METHODS: This study was a prospective assessment of temporal changes in DFT using a uniform testing algorithm, shock polarity and dual-coil active pectoral lead system. Thresholds were measured at implantation, before discharge and at long-term follow-up (70 +/- 40 weeks) in 50 patients. RESULTS: The DFTs were 9.2 +/- 5.4 J at implantation, 8.3 +/- 5.8 J before discharge and 6.9 +/- 3.6 J at long-term follow-up (p < 0.01 by analysis of variance; p < 0.05 for long-term follow-up vs. at implantation or before discharge). The effect was most marked in a prespecified subgroup with high implant DFTs (> or =15 J). No patient developed an inadequate safety margin (< 9 J) during follow-up. CONCLUSIONS: The DFTs declined significantly after implantation with an active pectoral, dual-coil transvenous lead system, and no clinically significant increases in DFT were observed. Therefore, routine defibrillation testing may not be required during the first two years after implantation with this lead system, in the absence of a change in the cardiac substrate or treatment with antiarrhythmic drugs.

A comparison of T-wave alternans, signal averaged electrocardiography and programmed ventricular stimulation for arrhythmia risk stratification.

OBJECTIVES: The goal of this study was to compare T-wave alternans (TWA), signal-averaged electrocardiography (SAECG) and programmed ventricular stimulation (EPS) for arrhythmia risk stratification in patients undergoing electrophysiology study. BACKGROUND: Accurate identification of patients at increased risk for sustained ventricular arrhythmias is critical to prevent sudden cardiac death. T-wave alternans is a heart rate dependent measure of repolarization that correlates with arrhythmia vulnerability in animal and human studies. Signal-averaged electrocardiography and EPS are more established tests used for risk stratification. METHODS: This was a prospective, multicenter trial of 313 patients in sinus rhythm who were undergoing electrophysiologic study. T-wave alternans, assessed with bicycle ergometry, and SAECG were measured before EPS. The primary end point was sudden cardiac death, sustained ventricular tachycardia, ventricular fibrillation or appropriate implantable defibrillator (ICD) therapy, and the secondary end point was any of these arrhythmias or all-cause mortality. RESULTS: Kaplan-Meier survival analysis of the primary end point showed that TWA predicted events with a relative risk of 10.9, EPS had a relative risk of 7.1 and SAECG had a relative risk of 4.5. The relative risks for the secondary end point were 13.9, 4.7 and 3.3, respectively (p < 0.05). Multivariate analysis of 11 clinical parameters identified only TWA and EPS as independent predictors of events. In the prespecified subgroup with known or suspected ventricular arrhythmias, TWA predicted primary end points with a relative risk of 6.1 and secondary end points with a relative risk of 8.0. CONCLUSIONS: T-wave alternans is a strong independent predictor of spontaneous ventricular arrhythmias or death. It performed as well as programmed stimulation and better than SAECG in risk stratifying patients for life-threatening arrhythmias.

Signal transduction by the antigen receptors of B and T lymphocytes.

B and T lymphocytes of the immune system recognize and destroy invading microorganisms but are tolerant to the cells and tissues of one's own body. The basis for this self/non-self-discrimination is the clonal nature of the B and T cell antigen receptors. Each lymphocyte has antigen receptors with a single unique antigen specificity. Multiple mechanisms ensure that self-reactive lymphocytes are eliminated or silenced whereas lymphocytes directed against foreign antigens are activated only when the appropriate antigen is present. The key element in these processes is the ability of the antigen receptors to transmit signals to the interior of the lymphocyte when they bind the antigen for which they are specific. Whether these signals lead to activation, tolerance, or cell death is dependent on the maturation state of the lymphocytes as well as on signals from other receptors. We review the role of antigen receptor signaling in the development and activation of B and T lymphocytes and also describe the biochemical signaling mechanisms employed by these receptors. In addition, we discuss how signal transduction pathways activated by the antigen receptors may alter gene expression, regulate the cell cycle, and induce or prevent programmed cell death.

Hypomagnesemia is a frequent finding in the emergency department in patients with chest pain.

STUDY OBJECTIVE: To evaluate the frequency of low blood levels of total and ultrafilterable magnesium (total and ultrafilterable hypomagnesemia) in patients with chest pain in the emergency department, and to determine if hypomagnesemia is associated with other clinically important diagnostic and outcome variables in cardiac care. SETTING: An emergency department of a university teaching hospital. DESIGN: Prospective study of extracellular magnesium homeostasis in patients with chest pain in the emergency department and a cohort of patients without chest pain with a clinical indication for blood sampling. PATIENTS: During a 4-month period, 147 patients presenting to the emergency department were studied: 67 patients (mean +/- SD age, 61.4 +/- 13 years) with a chief complaint of chest pain (study group) and 80 patients (55.6 +/- 19 years) with other diagnoses (control group). RESULTS: Total and ultrafilterable hypomagnesemia occurred more frequently in patients with chest pain (20/67 [30%] and 9/67 [13%]) than in the control group (12/80 [15%] and 3/80 [4%]). Patients with a chief complaint of chest pain who were receiving diuretic medications were hypomagnesemic more frequently (9/16 [56%]) than patients not receiving diuretics (12/51 [23%]). In patients with chest pain admitted to the hospital with a diagnosis of "rule out" myocardial infarction, the frequency of hypokalemia was greater among hypomagnesemic patients (6/14 [43%]) than normomagnesemic patients (3/31 [10%]). A similar frequency of hypomagnesemia was noted in patients with a final diagnosis of myocardial infarction (4/15 [27%]) when compared with other patients admitted with chest pain (10/31 [32%]) in whom myocardial infarction was excluded. No association was noted among hypomagnesemia and length of hospital stay or the occurrence of hypotension or dysrhythmias. CONCLUSIONS: Total and ultrafilterable hypomagnesemia are frequent occurrences in patients with and without chest pain in the emergency department. Diuretic use is associated with hypomagnesemia in patients presenting with chest pain in the emergency department. These results support the concept that hypomagnesemia is common in patients with chest pain in the emergency department and is associated with hypokalemia but is not predictive of whether the patient with chest pain has had an acute myocardial infarction.

Examination of B lymphoid cell lines for membrane immunoglobulin-stimulated tyrosine phosphorylation and src-family tyrosine kinase mRNA expression.

Crosslinking of membrane immunoglobulin (mIg) on B cells induces two signal transduction pathways: protein tyrosine phosphorylation and phosphoinositide turnover. A panel of murine and human B cell-lines, representing different stages of B cell development, was examined for the presence of anti-immunoglobulin-induced protein tyrosine phosphorylation. Of 10 B cell lines examined, only one, the human Raji cell line, had no detectably induced protein tyrosine phosphorylation. The pattern of proteins that were phosphorylated on tyrosine in response to mIg crosslinking differed somewhat in cell lines representing different stages of B cell development. Differences in the levels of constitutive phosphorylation of proteins were also observed between the cell lines. The identity of the tyrosine kinase(s) activated by membrane immunoglobulin ligation is not known. However, members of the src family of intracellular tyrosine kinases have been implicated as signal transduction molecules. As the tyrosine phosphorylation of proteins is a general phenomenon of signal transduction by membrane immunoglobulin, the tyrosine kinase(s) activated by it might be expected to be present in all cell lines in which the tyrosine phosphorylation signalling occurs. Therefore we examined these B cells for expression of mRNAs encoding the eight known src-like tyrosine kinases. Surprisingly, all eight kinase mRNAs were expressed in at least some of the B cell lines examined. The expression pattern of the fyn, hck, and lck genes suggests that expression of these kinases may be developmentally regulated in the B cell lineage. Three of the kinases, p55blk, p53/p56lyn and p60src, were detected in all 10 B cell lines. Whereas the src gene shows a ubiquitous pattern of expression, the expression of the blk and lyn genes is mostly restricted to cells of hematopoietic origin, and more especially B lymphoid cells. Thus, p55blk and p53/p56lyn may be particularly good candidates for the membrane immunoglobulin-activated tyrosine kinase.

Protein kinase C-delta is a target of B-cell antigen receptor signaling.

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.

Effects of waveform and polarity on defibrillation thresholds in humans using a transvenous lead system.

Minimizing defibrillation thresholds is important to allow for implantation of downsized pulse generators with reduced outputs while maintaining an adequate defibrillation safety margin. Recent studies have demonstrated a significant reduction in monophasic defibrillation thresholds with a transvenous lead when the polarity was reversed (proximal coil = cathode). However, conflicting data exist concerning the effect of polarity reversal on biphasic defibrillation thresholds. The present study was designed to evaluate prospectively the effect of waveform shape and polarity on defibrillation thresholds in humans. The group studied consisted of 26 patients undergoing cardioverter-defibrillator implantation for standard indications. All data were obtained with a transvenous lead alone configuration. Defibrillation thresholds were determined using a step-down protocol with the initial waveform and polarity randomized. Reversing polarity significantly decreased the delivered energy at defibrillation threshold with monophasic waveforms (14.8 +/- 7.1 vs 20.4 +/- 8.9 J; p < 0.001), but had no effect on the overall efficacy of biphasic waveforms (11.1 +/- 5.5 vs 12.2 +/- 6.5 J). In the subgroup of patients with high biphasic defibrillation thresholds (> or = 15 J), reversing polarity decreased the defibrillation threshold from 18.2 +/- 5.1 to 13.3 +/- 5.8 J (p < 0.001). Similarly, the improvement in defibrillation thresholds with reversing polarity of monophasic waveforms was confined to the subgroup of patients with higher defibrillation thresholds. Therefore, the lack of group effect of polarity on biphasic defibrillation thresholds may be simply due to the overall lowering of defibrillation thresholds by this waveform.