Cardiac Resynchronization and Circulating Markers of Sarcoplasmic Reticulum Calcium Handling and Sudden Death Risk

Cardiac resynchronization therapy (CRT) can improve heart function and decrease arrhythmic events. We tested whether CRT altered circulating markers of calcium handling and sudden death risk. Circulating cardiac sodium channel messenger RNA (mRNA) splicing variants indicate arrhythmic risk, and a reduction in sarco/endoplasmic reticulum calcium adenosine triphosphatase 2a (SERCA2a) is thought to diminish contractility in heart failure. CRT was associated with a decreased proportion of circulating, nonfunctional sodium channels and improved SERCA2a mRNA expression. Patients without CRT did not have improvement in the biomarkers. These changes might explain the lower arrhythmic risk and improved contractility associated with CRT.

The ABCD (Alternans Before Cardioverter Defibrillator) Trial: strategies using T-wave alternans to improve efficiency of sudden cardiac death prevention

OBJECTIVES

Because risk stratification with electrophysiological study (EPS) improves efficiency but is invasive, we sought to determine whether noninvasive microvolt T-wave alternans (MTWA) testing could identify patients who benefit from implantable cardioverter-defibrillators (ICDs) as well as EPS.

BACKGROUND

Prevention of sudden cardiac death on the basis of left ventricular ejection fraction (LVEF) alone is inefficient, because most ICDs never deliver therapy.

METHODS

The ABCD (Alternans Before Cardioverter Defibrillator) trial is a multicenter prospective study that enrolled patients with ischemic cardiomyopathy (LVEF < or =0.40) and nonsustained ventricular tachycardia. All patients underwent MTWA and EPS. ICDs were mandated if either test was positive.

RESULTS

Of 566 patients followed for a median of 1.9 years, 39 (7.5%) met the primary end point of appropriate ICD discharge or sudden death at 1 year. As hypothesized, primary analysis showed that MTWA achieved 1-year positive (9%) and negative (95%) predictive values that were comparable to EPS (11% and 95%, respectively). In addition, secondary analysis showed that at the pre-specified 1-year end point, event rates were significantly higher in patients with both a positive MTWA-directed strategy (hazard ratio: 2.1, p = 0.03) and a positive EPS-directed strategy (hazard ratio: 2.4, p = 0.007). Moreover, the event rate in patients with both negative MTWA test and EPS was lower than in those with 2 positive tests (2% vs. 12%; p = 0.017).

CONCLUSIONS

The ABCD study is the first trial to use MTWA to guide prophylactic ICD insertion. Risk stratification strategies using noninvasive MTWA versus invasive EPS are comparable at 1 year and complementary when applied in combination. Strategies employing MTWA, EPS, or both might identify subsets of patients least likely to benefit from ICD insertion. (Study to Compare TWA Test and EPS Test for Predicting Patients at Risk for Life-Threatening Heart Rhythms [ABCD Study]; NCT00187291).

Coronary Sinus and Fossa Ovalis Ablation: Effect on Interatrial Conduction and Atrial Fibrillation

BACKGROUND

Interatrial conduction occurs via discrete pathways along the coronary sinus musculature, fossa ovalis region, and Bachman's bundle. We assessed the feasibility of altering interatrial conduction by selectively ablating two of these conduction pathways using a novel mesh electrode ablation catheter.

METHODS

Circular radiofrequency energy catheter ablation lesions were created in the proximal coronary sinus in four dogs and in both the fossa ovalis and the proximal coronary sinus regions in seven pigs. Interatrial conduction was assessed by analyzing intracardiac electrogram and noncontact isopotential mapping data. Inducibility of atrial fibrillation was assessed before and after ablation (in six pigs).

RESULTS

Ablation lesions in the proximal coronary sinus eliminated interatrial conduction along the coronary sinus musculature in four dogs and five of seven pigs. Ablation lesions in the fossa ovalis region eliminated interatrial conduction via midseptal pathways in six of seven pigs. Atrial fibrillation, inducible in five of seven pigs at baseline, was rendered noninducible in all five. There was no adverse effect on AV nodal conduction.

CONCLUSIONS

(1) Using a novel mesh electrode ablation catheter, we were able to ablate interatrial conduction pathways along the proximal coronary sinus and fossa ovalis regions. (2) This altered interatrial conduction and altered atrial fibrillation inducibility and maintenance. (3) Catheter ablation of interatrial conduction pathways may be useful in the therapy of atrial fibrillation.

True Bipolar Defibrillator Leads Have Increased Sensing Latency and Threshold Compared with the Integrated Bipolar Configuration

BACKGROUND

Dual-coil implantable defibrillator (ICD) leads with true bipolar pacing and sensing (quadripolar leads) have been introduced to provide improved sensing characteristics without sacrificing defibrillation efficacy. Electrode configuration has been shown to have little effect on the amplitude or slew rate of the intracardiac electrogram, but does have an effect on the duration of the sensed electrogram. Closer spacing of the electrodes and smaller surface area of the anode may, therefore, result in a different latency of sensing relative to the onset of the QRS complex.

METHODS

We tested the difference in ventricular sensing latency between integrated bipolar and true bipolar electrode configurations in 40 patients undergoing ICD implantation for standard indications (Medtronic Sprint Quattro lead in 26 and St. Jude Riata in 16). In addition, we compared R wave amplitude, pacing threshold, impedance, and slew rate.

RESULTS

Sensing latency was significantly longer in the true bipolar configuration (Medtronic Sprint Quattro 45.2 +/- 14.7 msec in the true bipolar configuration, vs 37.4 +/- 18.2 msec in the integrated bipolar configuration, and St. Jude Riata, 43.5 +/- 9.8 msec true bipolar, vs 33.8 +/- 10.1 msec integrated bipolar, P < 0.01). There was no difference in R wave amplitude or slew rate. Pacing threshold and impedance were also greater in the true bipolar configuration than in the integrated bipolar configuration.

CONCLUSION

The true bipolar configuration has a longer sensing latency than the integrated bipolar configuration. In some patients, this may require a longer programmed AV delay to avoid ventricular pseudofusion.

Effect of an active abdominal pulse generator on defibrillation thresholds with a dual-coil, transvenous ICD lead system

INTRODUCTION

Many patients with implantable cardioverter defibrillators (ICDs) have older lead systems, which are usually not replaced at the time of pulse generator replacement unless a malfunction is noted. Therefore, optimization of defibrillation with these lead systems is clinically important. The objective of this prospective study was to determine if an active abdominal pulse generator (Can) affects chronic defibrillation thresholds (DFTs) with a dual-coil, transvenous ICD lead system.

METHODS AND RESULTS

The study population consisted of 39 patients who presented for routine abdominal pulse generator replacement. Each patient underwent two assessments of DFT using a step-down protocol, with the order of testing randomized. The distal right ventricular (RV) coil was the anode for the first phase of the biphasic shocks. The proximal superior vena cava (SVC) coil was the cathode for the Lead Alone configuration (RV --> SVC). For the Active Can configuration, the SVC coil and Can were connected electrically as the cathode (RV --> SVC + Can). The Active Can configuration was associated with a significant decrease in shock impedance (39.5 +/- 5.8 Omega vs. 50.0 +/- 7.6 Omega, P < 0.01) and a significant increase in peak current (8.3 +/- 2.6 A vs. 7.2 +/- 2.4 A, P < 0.01). There was no significant difference in DFT energy (9.0 +/- 4.6 J vs. 9.8 +/- 5.2 J) or leading edge voltage (319 +/- 86 V vs. 315 +/- 83 V). An adequate safety margin for defibrillation (> or =10 J) was present in all patients with both shocking configurations.

CONCLUSION

DFTs are similar with the Active Can and Lead Alone configurations when a dual-coil, transvenous lead is used with a left abdominal pulse generator. Since most commercially available ICDs are only available with an active can, our data support the use of an active can device with this lead system for patients who present for routine pulse generator replacement.

Enhanced Detection of Arrhythmia Vulnerability Using T Wave Alternans, Left Ventricular Ejection Fraction, and Programmed Ventricular Stimulation:. A Prospective Study in Subjects with Chronic Ischemic Heart Disease

INTRODUCTION

In previous studies, the prognostic value of T wave alternans (TWA) was similar to that of programmed ventricular stimulation (PVS). However, presently it is unclear if TWA and PVS identify the same patients or provide complementary risk stratification information. In addition, the effects of left ventricular ejection fraction (LVEF) on the prognostic value of TWA are unknown. The aim of this study was to determine if combined assessment of TWA, LVEF, and PVS improves arrhythmia risk stratification.

METHODS AND RESULTS

This was a prospective study of 144 patients with coronary artery disease and LVEF < or =40% who were referred for PVS for standard clinical indications. The endpoint was the combined incidence of death, sustained ventricular arrhythmias, and appropriate implantable cardioverter defibrillator (ICD) therapy. TWA (hazard ratio 2.2, P = 0.03) and PVS (hazard ratio 1.9, P = 0.05) both were significant predictors of endpoint events, and TWA was the only independent predictor. LVEF markedly influenced the prognostic value of TWA, which was a potent predictor of events in subjects with LVEF between 30% and 40% (event rates: TWA+ 36%, TWA- 0%, P = 0.001) but did not predict events in subjects with LVEF <30% (hazard ratio 1.1, P > 0.5). PVS successfully identified additional low-risk patients within the cohort with negative or indeterminate TWA results (hazard ratio 4.7, P = 0.015) but did not provide incremental prognostic information for TWA+ patients (hazard ratio 0.9, P > 0.5).

CONCLUSION

The combined use of TWA, LVEF, and PVS is a promising new approach to arrhythmia risk stratification that permits identification of high-risk and very-low-risk patients.

Primary prevention of sudden cardiac death: trials in patients with coronary artery disease

Over the past decade, four randomized, controlled trials have evaluated therapies for prevention of sudden cardiac death in patients with coronary disease. Three of the four trials have shown significant reductions in mortality with implanted defibrillators. Two studies failed to demonstrate any benefit from pharmacologic antiarrhythmic therapy. The results of these studies in similar patient populations have erased any doubt regarding the ability of implanted defibrillators to reduce the risk of sudden death in patients with coronary disease. Our major challenge at this time is understanding how best to utilize this therapy in order to bring the benefit to the maximum number of patients while minimizing expense.

Role of the transverse-axial tubule system in generating calcium sparks and calcium transients in rat atrial myocytes

Cardiac atrial cells lack a regular system of transverse tubules like that in cardiac ventricular cells. Nevertheless, many atrial cells do possess an irregular internal transverse-axial tubular system (TATS). To investigate the possible role of the TATS in excitation-contraction coupling in atrial myocytes, we visualized the TATS (labelled with the fluorescent indicator, Di-8-ANEPPS) simultaneously with Ca2+ transients and/or Ca2+ sparks (fluo-4). In confocal transverse linescan images of field-stimulated cells, whole-cell Ca2+ transients had two morphologies: 'U-shaped' transients and irregular or 'W-shaped' transients with a varying number of points of origin of the Ca2+ transient. About half (54 %, n =289 cells, 13 animals) of the cells had a TATS. Cells with TATS had a larger mean diameter (13.2 +/- 2.8 microm) than cells without TATS (11.7 +/- 2.0 microm) and were more common in the left atrium (n = 206 cells; left atrium: 76 with TATS, 30 without TATS; right atrium: 42 with TATS, 58 without TATS). Simultaneous measurement of Ca2+ sparks and sarcolemmal structures showed that cells without TATS had U-shaped transients that started at the cell periphery, and cells with TATS had W-shaped transients that began simultaneously at the cell periphery and the TATS. Most (82 out of 102 from 31 cells) 'spontaneous' (non-depolarized) Ca2+ sparks occurred within 1 microm of a sarcolemmal structure (cell periphery or TATS), and 33 % occurred within 1 pixel (0.125 microm). We conclude that the presence of a sarcolemmal membrane either at the cell periphery or in the TATS in close apposition to the sarcoplasmic reticulum is required for the initiation of an evoked Ca2+ transient and for spontaneous Ca2+ sparks.

Management of the non-inducible patient

Management of the patient without inducible arrhythmias is dictated by the clinical setting in which the arrhythmias occur. Decisions must be based on whether the patient is being treated for symptomatic arrhythmias, or is undergoing evaluation of risk for potentially lethal arrhythmias. The management is influenced by the anatomic substrate, as well as the clinical presentation. As with all diagnostic tests, the significance of the electrophysiology study depends on the clinical context, and this type of test reflects but one mechanism for tachycardia. Finally, it is critical to remember that the results of published clinical trials can be used to guide management decisions, only when the same stimulation protocol utilized in the trials is employed, and the patient has the same characteristics as those enrolled in the trial.

Exercise is superior to pacing for T wave alternans measurement in subjects with chronic coronary artery disease and left ventricular dysfunction

INTRODUCTION

T wave alternans (TWA) is a heart rate-dependent marker of vulnerability to ventricular arrhythmias. Atrial pacing and exercise both are used as provocative stimuli to elicit TWA. However, the prognostic value of the two testing methods has not been compared. The aim of this prospective study was to compare the prognostic value of TWA measured during bicycle exercise and atrial pacing in a large cohort of high-risk patients with ischemic heart disease and left ventricular dysfunction.

METHODS AND RESULTS

This was a prospective study of 251 patients with coronary artery disease and left ventricular dysfunction who were referred for electrophysiologic studies (EPS) for standard clinical indications. Patients underwent TWA testing using bicycle ergometry (exercise TWA, n = 144) and/or atrial pacing (pacing TWA, n = 178). The primary endpoint was the combined incidence of death, sustained ventricular arrhythmias, and appropriate implantable cardioverter defibrillator therapy. The predictive value of exercise and pacing TWA for EPS results and for endpoint events was determined. Exercise and pacing TWA both were significant predictors of EPS results (odds ratios 3.0 and 2.9 respectively, P < 0.02). Kaplan-Meier survival analysis of the primary endpoint revealed that exercise TWA was a significant predictor of events (hazard ratio 2.2, P = 0.03). In contrast, pacing TWA had no prognostic value for endpoint events (hazard ratio 1.1, P = 0.8).

CONCLUSION

TWA should be measured during exercise when it is used for clinical risk stratification. EPS results may not be an adequate surrogate for spontaneous events when evaluating new risk stratification tests.

Influence of QRS duration on the prognostic value of T wave alternans

INTRODUCTION

T wave alternans (TWA) is a promising new noninvasive marker of arrhythmia vulnerability that quantifies beat-to-beat changes in ventricular repolarization. Secondary repolarization abnormalities are common in subjects with wide QRS complexes. However, the relationship between TWA and QRS prolongation has not been evaluated. The goal of this study was to determine if QRS prolongation influences the prevalence or prognostic value of TWA.

METHODS AND RESULTS

The study consisted of 108 consecutive patients with coronary artery disease and left ventricular ejection fraction < or = 40% who were referred for electrophysiologic studies. Patients underwent TWA testing using bicycle ergometry in the absence of beta-blockers or antiarrhythmic drugs. The primary endpoint was the combined incidence of death, sustained ventricular arrhythmias, and appropriate implantable cardioverter defibrillator therapy. The prognostic value of TWA was assessed in the entire cohort and in two subgroups: QRS < 120 msec (normal, n = 62) and QRS > or = 120 msec (prolonged, n = 46). TWA (hazard ratio 2.2, P = 0.03) and QRS prolongation (hazard ratio 2.2, P = 0.01) were both significant and independent predictors of arrhythmic events. QRS prolongation had no effect on the prevalence of positive TWA tests (QRS < 120 msec: 48%, QRS > or = 120 msec: 50%, P = NS). TWA was a highly significant predictor of events in patients with a normal QRS (hazard ratio 5.8, P = 0.02). In contrast, TWA was not useful for risk stratification in subjects with QRS prolongation (hazard ratio 1.1, P = 0.8).

CONCLUSION

TWA is useful only for risk stratification in the absence of QRS prolongation. The presence of QRS prolongation and left ventricular ejection fraction < or = 40% may be sufficient evidence of an adverse prognosis that additional risk stratification is not useful or necessary.

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.

Current approaches to evaluation and management of patients with ventricular arrhythmias

The clinical manifestations of ventricular arrhythmias encompass a broad spectrum, from complete absence of symptoms to sudden death. Although our understanding of the pathophysiology and natural history of these arrhythmias has advanced significantly over the past decade, large gaps in our knowledge remain, especially in patients with heart failure not due to coronary artery disease. We have learned much about the appropriate roles of antiarrhythmic drugs and implantable defibrillators in the prevention of sudden death. Studies performed over the past decade have made clear that the primary treatment for patients at high risk for life-threatening ventricular arrhythmias should be the implantable defibrillator. However, specific syndromes causing ventricular tachyarrhythmias are being recognized, and care must be individualized. Although hospital mortality from acute myocardial infarction has decreased as a result of newer therapies, sudden death after hospital discharge remains an important problem, causing at least 30% of post-infarction deaths, even in patients who have received thrombolytic therapy. Two independent studies have confirmed that patients with asymptomatic non-sustained ventricular tachycardia in the presence of left ventricular ejection fraction < .40 after myocardial infarction who have sustained ventricular tachycardia inducible by electrophysiologic study are at significant risk for sudden death. This risk is significantly reduced by ICD, but not pharmacologic, antiarrhythmic therapy. Our major challenge at this time is not how best to treat high risk patients, but how best to identify them prior to events. Finally, physicians should be aware that many symptomatic ventricular tachycardias are now curable at low risk, using catheters to deliver radiofrequency energy.

regA, a Volvox gene that plays a central role in germ-soma differentiation, encodes a novel regulatory protein

Volvox has two cell types: mortal somatic cells and immortal germ cells. Here we describe the transposon-tagging, cloning and characterization of regA, which plays a central role as a master regulatory gene in Volvox germ-soma differentiation by suppressing reproductive activities in somatic cells. The 12.5 kb regA transcription unit generates a 6,725 nucleotide mRNA that appears at the beginning of somatic cell differentiation, and that encodes a 111 kDa RegA protein that localizes to the nucleus, and has an unusual abundance of alanine, glutamine and proline. This is a compositional feature shared by functional domains of many ‘active’ repressors. These findings are consistent with the hypothesis that RegA acts in somatic cells to repress transcription of genes required for growth and reproduction, including 13 genes whose products are required for chloroplast biogenesis.

Deployment of a previously embolized, unexpanded, and disarticulated Palmaz-Schatz stent

Stent embolization is a rare but acknowledged complication of placement of disarticulated (half) Palmaz-Schatz stents. We report a case in which we diagnosed a previously unrecognized, embolized, undeployed half-stent in the distal LAD, causing slow flow, and then deployed the stent where it lay, resulting in improved flow. The literature on treatment of coronary stent embolization and on cutting and preparing half-stents for deployment is discussed.

Chronic rise in monophasic defibrillation thresholds with a transvenous lead system

This study was a prospective evaluation of chronic changes of defibrillation thresholds in 31 clinically stable patients with a single transvenous lead, optimal shock polarity, and uniform testing protocol. At a mean follow-up of 273 +/- 146 days, defibrillation thresholds increased 26%, from 13.2 +/- 5.6 J to 17.1 +/- 6:0 J (p < 0.001), and shock impedance increased from 46.2 +/- 7.0 omega to 51.2 +/- 6.2 omega (p < 0.001).

Nuclear transformation of Volvox carteri

Stable nuclear transformation of Volvox carteri was achieved using the cloned V. carteri nitA+ gene (which encodes nitrate reductase) to complement a nitA- mutation. Following bombardment of mutant cells with plasmid-coated gold particles, putative transformants able to utilize nitrate as a nitrogen source were recovered with an efficiency of approximately 2.5 x 10(5). DNA analysis indicated that the plasmid integrated into the genome, often in multiple copies, at sites other than the nitA locus. Cotransformants were recovered with a frequency of 40-80% when cells were cobombarded with a selected and an unselected marker. Thus, V. carteri becomes one of the simplest multicellular organisms that is accessible to detailed molecular studies of genes regulating cellular differentiation and morphogenesis.

The relationship between cell size and cell fate in Volvox carteri

In Volvox carteri development, visibly asymmetric cleavage divisions set apart large embryonic cells that will become asexual reproductive cells (gonidia) from smaller cells that will produce terminally differentiated somatic cells. Three mechanisms have been proposed to explain how asymmetric division leads to cell specification in Volvox: (a) by a direct effect of cell size (or a property derived from it) on cell specification, (b) by segregation of a cytoplasmic factor resembling germ plasm into large cells, and (c) by a combined effect of differences in cytoplasmic quality and cytoplasmic quantity. In this study a variety of V. carteri embryos with genetically and experimentally altered patterns of development were examined in an attempt to distinguish among these hypotheses. No evidence was found for regionally specialized cytoplasm that is essential for gonidial specification. In all cases studied, cells with a diameter > approximately 8 microns at the end of cleavage--no matter where or how these cells had been produced in the embryo--developed as gonidia. Instructive observations in this regard were obtained by three different experimental interventions. (a) When heat shock was used to interrupt cleavage prematurely, so that presumptive somatic cells were left much larger than they normally would be at the end of cleavage, most cells differentiated as gonidia. This result was obtained both with wild-type embryos that had already divided asymmetrically (and should have segregated any cytoplasmic determinants involved in cell specification) and with embryos of a mutant that normally produces only somatic cells. (b) When individual wild-type blastomeres were isolated at the 16-cell stage, both the anterior blastomeres that normally produce two gonidia each and the posterior blastomeres that normally produce no gonidia underwent modified cleavage patterns and each produced an average of one large cell that developed as a gonidium. (c) When large cells were created microsurgically in a region of the embryo that normally makes only somatic cells, these large cells became gonidia. These data argue strongly for a central role of cell size in germ/soma specification in Volvox carteri, but leave open the question of how differences in cell size are actually transduced into differences in gene expression.

Molecular phylogeny of the volvocine flagellates

Phylogenetic studies of approximately 2,000 bases of sequence from the large and small nuclear-encoded ribosomal RNAs are used to investigate the origins of the genus Volvox. The colonial and multicellular genera currently placed in the family Volvocaceae form a monophyletic group that is significantly closer phylogenetically to Chlamydomonas reinhardtii than it is to the other unicellular green flagellates that were tested, including Chlamydomonas eugametos, Chlorella pyrenoidosa, and Haematococcus lacustris. Statistical analysis of 251 phylogenetically informative nucleotide positions rejects the "volvocine lineage" hypothesis, which postulates a monophyletic evolutionary progression from unicellular organisms (such as Chlamydomonas), through colonial organisms (e.g., Gonium, Pandorina, Eudorina, and Pleodorina) demonstrating increasing size, cell number, and tendency toward cellular differentiation, to multicellular organisms having fully differentiated somatic and reproductive cells (in the genus Volvox). The genus Volvox appears not to be monophyletic. Volvox capensis falls outside a lineage containing other representatives of Volvox (V. aureus, V. carteri, and V. obversus), and both of these Volvox lineages are more closely related to certain colonial genera than they are to each other. This implies either a diphyletic origin of Volvox from different colonial volvocacean ancestors, a phylogenetic derivation of some of the colonial genera from a multicellular (i.e., Volvox) ancestor, or both. Considered together with previously published observations, these results suggest that the different levels of organizational and developmental complexity found in the Volvocaceae represent alternative stable states, among which evolutionary transitions have occurred several times during the phylogenetic history of this group.

Reversible decerebrate posturing after profound and prolonged hypoglycemia

Decerebrate rigidity is one of several reversible neurological abnormalities which have been observed in the setting of metabolic coma. We present the case of a patient who recovered fully from prolonged decerebrate rigidity associated with hypoglycemic coma. This case emphasizes the possibility of recovery from severe, prolonged hypoglycemia.

Heat shock elicits production of sexual inducer in Volvox

In the green alga Volvox carteri, heat shock had an unusual and adaptive effect mediated by induced production of a well-defined effector molecule. Females of this species normally reproduce asexually in the absence of a potent sexual inducer produced by mature sexual males, but they generated egg-bearing sexual daughters after a brief exposure to elevated temperatures. This response involved an "autoinduction" of sexuality, in which heat-shocked somatic cells made and released the sexual inducer, which then redirected development of the reproductive cells. Males, including a sterile mutant incapable of producing inducer in the usual manner, also produced the inducer in response to heat shock. The phenomenon probably is of significance in the wild, where Volvox reproduces asexually in temporary ponds in spring but becomes sexual and produces dormant, overwintering zygotes before the ponds dry up in the summer heat.

Translational regulation of protein synthesis, in response to light, at a critical stage of Volvox development

In Volvox cultures synchronized by a light-dark cycle, juveniles containing presumptive somatic and reproductive cells are produced during the dark, but their cells do not differentiate until after the lights come on. The pattern of protein synthesis changes rapidly after the lights come on. Action spectra and effects of photosynthesis inhibitors indicate that this protein synthetic change is not simply a consequence of renewed flow of energy from illuminated chloroplasts. Actinomycin, at a level adequate to block the response to heat shock, has virtually no effect on the response of the same cells to light; furthermore, RNAs isolated from unilluminated and illuminated juveniles yield indistinguishable in vitro translation products. We conclude, therefore, that this effect of light is exerted almost exclusively at the translational level, generating one of the most striking examples of translational regulation yet described.

Protein synthetic patterns during the asexual life cycle of Volvox carteri

The polypeptide labeling patterns of somatic cells, gonidia (asexual reproductive cells), embryos, and juvenile spheroids of Volvox carteri cultures synchronized by a light/dark cycle were studied as a function of developmental stage and incubation condition. Specimens were exposed to 35SO=4 for 1-hr periods at selected intervals throughout the asexual life cycle; proteins were then extracted and analyzed by one-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) followed by fluorography. Although sulfation accounts for more than half the 35S incorporated, the conditions of extraction and electrophoresis employed resulted in exclusion of most sulfated products and inclusion of nearly all products bearing incorporated sulfur amino acids in the electrophoretic analysis. Hence SDS-PAGE profiles reflect relative rates of synthesis of major polypeptides. The first phase of these studies involved examination of stage-specific differences in protein synthetic patterns. Because a single developmental stage exhibits different protein synthetic patterns in light and darkness, detailed developmental comparisons were made only on organisms or cells exposed to label in the light. They yielded the following results: Shortly after the completion of embryogenesis (while all cells are still linked by numerous cytoplasmic bridges) presumptive somatic cells and gonidia exhibit a nearly identical pattern of labeling of the major polypeptides. In just a few hours, however, as cytoplasmic bridges begin to break down, the synthetic patterns of the two cell types begin to diverge; with passing time this divergence becomes progressively greater. By the time gonidia are mature, the patterns of labeling of major polypeptides by somatic cells and gonidia exhibit far more differences than similarities. Embryos derived from these mature gonidia then exhibit numerous, reproducible, stage-specific changes in polypeptide labeling throughout embryogenesis. However, two glycoproteins that previous authors implicated in the control of the differentiative cleavage division are here shown to be labeled in the parental somatic cells, not in the embryos as was previously supposed; hence a central role for them in embryonic development seems highly unlikely. In the second phase of this study the effects of light on protein synthetic patterns of organisms at selected developmental stages were analyzed. At all stages marked, rapid, reversible changes in the pattern of labeling of major polypeptides occur when cultures are transferred from light to dark or vice versa, but these changes are most marked in juvenile spheroids at the end of the dark period during which they had completed their embryogenesis. Some, but by no means all, of the changes induced by light can be attributed to stimulated synthesis of chloroplast proteins, on both chloroplast and cytosol ribosomes. The proteins made at the beginning of one light period are not identical to those made at the end of the preceding light period...

Carrier-mediated Uptake of Arginine and Urea by Chlamydomonas reinhardtii

Chlamydomonas reinhardtii possesses a high affinity, highly specific carrier involved in uptake of exogenous arginine. Carrier-mediated uptake of other amino acids cannot be detected, even in cultures maintained on amino acids as a nitrogen source or starved for nitrogen. This fact may contribute to the difficulty of isolating strains auxotrophic for amino acids other than arginine; conventional selection media may not supply adequate quantities of amino acids to permit growth of auxotrophs. A urea carrier is also present in C. reinhardtii but is readily distinguished from the arginine carrier on the basis of kinetic properties and sensitivity to a range of structural analogs. Ammonia appears to play a major role in regulating (depressing) activity of the arginine uptake system. Activity of the urea uptake system is elevated in nitrogen-starved cultures and elevated even further in the presence of urea or arginine. Extensive, independent fluctuations in the two uptake systems observed in semisynchronous cultures suggest that both are subject to modulation by a complex set of interacting endogenous and exogenous factors.

Carrier-mediated Uptake of Arginine and Urea by Volvox carteri f. nagariensis

Volvox carteri f. nagariensis takes up arginine via a high affinity, highly specific carrier, whereas carriers for neutral and acidic amino acids cannot be detected (even in nitrogen-starved cultures). Exogenous arginine is accumulated against a steep concentration gradient and is incorporated into protein with high efficiency, but it is not catabolized to any significant extent and will not serve as a nitrogen source adequate to support growth. Urea is also taken up by a saturable carrier, but several lines of evidence indicate that the arginine and urea carriers are distinct and different. Preexposure to arginine suppresses arginine uptake while stimulating urea uptake. The K(i) values observed for reciprocal, competitive inhibition of uptake by arginine and urea are orders of magnitude different from the respective K(m) values for uptake. The two uptake systems show entirely different patterns of sensitivity to inhibition by structural analogs. Finally, the V(max) values for arginine and urea uptake fluctuate independently (but in a regular pattern) during the asexual life cycle. The fluctuations of urea uptake activity are of considerable magnitude and appear to be linked to key phases of the developmental program.