RNA viruses as complex adaptive systems

RNA viruses have high mutation rates and so their populations exist as dynamic and complex mutant distributions. It has been consistently observed that when challenged with a new environment, viral populations adapt following hyperbolic-like kinetics: adaptation is initially very rapid, but then slows down as fitness reaches an asymptotic value. These adaptive dynamics have been explained in terms of populations moving towards the top of peaks on rugged fitness landscapes. Fitness fluctuations of varying magnitude are observed during adaptation. Often the presence of fluctuations in the evolution of physical systems indicates some form of self-organization, or where many components of the system are simultaneously involved. Here we analyze data from several in vitro evolution experiments carried out with vesicular stomatitis virus (VSV) looking for the signature of criticality and scaling. Long-range fitness correlations have been detected during the adaptive process. We also found that the magnitude of fitness fluctuations, far from being trivial, conform to a Weibull probability distribution function, suggesting that viral adaptation belongs to a broad category of phenomena previously documented in other fields and related with emergence.

Following the very initial growth of biological RNA viral clones

Due to their extremely high genetic diversity, which is a direct consequence of high mutation rates, RNA viruses are often described as molecular quasispecies. According to this theory, RNA virus populations cannot be understood in terms of individual viral clones, as they are clouds of interconnected mutants, but this prediction has not yet been demonstrated experimentally. The goal of this study was to determine the fitness of individual clones sampled from a given RNA virus population, a necessary previous step to test the above prediction. To do so, limiting dilutions of a vesicular stomatitis virus population were employed to isolate single viral clones and their initial growth dynamics were followed, corresponding to the release of the first few hundred viral particles. This technique is useful for estimating basic fitness parameters, such as intracellular growth rate, viral yield per cell, rate at which cells are infected and time spent in cell-to-cell transmission. A combination of these parameters allows estimation of the fitness of individual clones, which seems to be determined mainly by their ability to complete infection cycles more quickly. Interestingly, fitness was systematically higher for initial clones than for their derived populations. In addition to environmental changes, such as cellular defence mechanisms, these differences are attributable to high RNA virus mutation rates.

Mode of selection and experimental evolution of antiviral drugs resistance in vesicular stomatitis virus

The possession of an antiviral resistance mutation benefits a virus when the corresponding antiviral is present. But does the resistant virus pay a fitness cost when the antiviral is absent? Would an evolutionary history of association between a genotype and a resistance mutation overcome this cost by changes compensating the harmful side-effect of resistance mutations? Are combined therapies more effective against the rise of resistant viruses or against evolutionary compensations? To explore all these questions, we took an experimental evolution approach. After selecting vesicular stomatitis virus (VSV) populations able to replicate under increasing concentrations of ribavirin and/or alpha-interferon, we evolved them for more than 100 generations under sub-inhibitory concentrations of the corresponding antivirals, allowing for evolutionary compensation. Our results show that resistance for these two antivirals was not easily achieved, being the selected populations generally less fit than the ancestrals both in presence and absence of the antivirals. Evolution in presence of sub-inhibitory concentrations of antivirals compensated for the reduction in fitness in presence of antiviral therapy.

Amebic liver abscess with bacterial superinfection in a patient with no epidemiologic risk factors

The amebic liver abscess is uncommon in developed countries like Spain, but the incidence is increasing probably due to the migratory movements of the population. We report a case of an amebic abscess, initially unsuspected due to the absence of epidemiologic risk factors and the negative serology for amebiasis, in the early stages of the disease.

The contribution of epistasis to the architecture of fitness in an RNA virus

The tendency for genetic architectures to exhibit epistasis among mutations plays a central role in the modern synthesis of evolutionary biology and in theoretical descriptions of many evolutionary processes. Nevertheless, few studies unquestionably show whether, and how, mutations typically interact. Beneficial mutations are especially difficult to identify because of their scarcity. Consequently, epistasis among pairs of this important class of mutations has, to our knowledge, never before been explored. Interactions among genome components should be of special relevance in compacted genomes such as those of RNA viruses. To tackle these issues, we first generated 47 genotypes of vesicular stomatitis virus carrying pairs of nucleotide substitution mutations whose separated and combined deleterious effects on fitness were determined. Several pairs exhibited significant interactions for fitness, including antagonistic and synergistic epistasis. Synthetic lethals represented 50% of the latter. In a second set of experiments, 15 genotypes carrying pairs of beneficial mutations were also created. In this case, all significant interactions were antagonistic. Our results show that the architecture of the fitness depends on complex interactions among genome components.

Usefulness of C-reactive protein and left ventricular function for risk assessment in survivors of acute myocardial infarction

The additional prognostic information provided by C-reactive protein (CRP) to parameters of left ventricular function in survivors of acute myocardial infarction (AMI) was investigated in 665 patients (326 with ST elevation and 339 with non-ST elevation). Cox multivariable analysis identified the following predictors of 6-month cardiac death: age (per 5 years hazard ratio [HR] 1.2, 95% confidence interval [CI] 1.1 to 1.4, p = 0.004), Killip class >I at presentation (HR 2.4, 95% CI 1.3 to 4.5, p = 0.0001), a reduced ejection fraction (per 5% HR 1.3, 95% CI 1.2 to 1.4, p = 0.0001), and greater CRP (per 5 mg/L HR 1.02, 95% CI 1.01 to 1.04, p = 0.02); the C-index of the model was 0.77 without and 0.78 with CRP. CRP is associated with mortality in addition to age and parameters of ventricular function (Killip class and ejection fraction) in survivors of AMI, although the relevance of its additive predictive role seems marginal.

[Prognostic value of Charlson comorbidity index at 30 days and 1 year after acute myocardial infarction]

INTRODUCTION AND OBJECTIVES

The Charlson comorbidity index (CCI), an indicator of comorbidity, has been used as an adjusting variable in multivariate models. Because of its prognostic value per se for cardiovascular complications after acute myocardial infarction (AMI), we sought to determine the predictive value of the CCI for all-cause mortality and recurrent AMI 30 days and 1 year after the index event.

PATIENTS AND METHOD

We analyzed 1035 consecutive patients admitted with the diagnosis of AMI (ST elevation=508 and non-ST elevation=527). The composite endpoint was determined after 30 days (13.9%) and 1 year (26.3%) of follow-up. The CCI was calculated on admission, and other variables with prognostic value were also recorded. CCI was stratified in 4 categories: 1: CCI=0 (control), 2: CCI=1, 3: CCI=2,4: CCI> or =3. Cox proportional risks analysis was used for the multivariate analysis, and the C-statistic was calculated to assess the discriminative power of the models.

RESULTS

Hazard ratios (95% CI) estimated for each category of CCI were: 2=1.69 (1.10-2.59), 3=1.78 (1.08-2.92) and 4=1.57 (0.87-2.83) at 30 days; 2=1.62 (1.18-2.23), 3=2.00 (1.39-2.89) and 4=2.24 (1.50-3.36) at 1 year. Comparisons with the C-statistic between the nested multivariate models (with and without CCI) yielded values of 0.765 vs 0.750 after 30 days, and 0.751 vs 0.735 after 1 year.

CONCLUSIONS

Our data indicate that CCI is an independent predictor of mortality or recurrent AMI 30 days and 1 year after the index AMI.

The distribution of fitness effects caused by single-nucleotide substitutions in an RNA virus

Little is known about the mutational fitness effects associated with single-nucleotide substitutions on RNA viral genomes. Here, we used site-directed mutagenesis to create 91 single mutant clones of vesicular stomatitis virus derived from a common ancestral cDNA and performed competition experiments to measure the relative fitness of each mutant. The distribution of nonlethal deleterious effects was highly skewed and had a long, flat tail. As expected, fitness effects depended on whether mutations were chosen at random or reproduced previously described ones. The effect of random deleterious mutations was well described by a log-normal distribution, with -19% reduction of average fitness; the effects distribution of preobserved deleterious mutations was better explained by a beta model. The fit of both models was improved when combined with a uniform distribution. Up to 40% of random mutations were lethal. The proportion of beneficial mutations was unexpectedly high. Beneficial effects followed a gamma distribution, with expected fitness increases of 1% for random mutations and 5% for preobserved mutations.

Natural selection and the organ-specific differentiation of HIV-1 V3 hypervariable region

The existence of organ-specific HIV-1 populations within infected hosts has been studied for many years; nonetheless results reported by different authors are somewhat discrepant. To tackle this problem, we used a population genetics approach to analyze previously published data from the V3 hypervariable region of the envelope env gene. Our results are compatible with a population subdivision by organs in 95% of individuals analyzed at autopsy. In addition, populations infecting the nervous system and testicles clearly appear as differentiated subsets of the so-called macrophage-tropic variants. Liver and kidney may harbor differentiated populations as well. Although it is widely accepted that organ compartmentalization arises as a consequence of different selective pressures imposed by different organs, a definitive demonstration has not yet been provided. Our analysis of the pattern of synonymous and nonsynonymous nucleotide substitutions provides evidence supporting this hypothesis, without discarding the role of other evolutionary processes. In contrast, positive selection does not seem to be the mechanism responsible for the evolution of patient-specific sequences.

Preoperative use of sotalol versus atenolol for atrial fibrillation after cardiac surgery

BACKGROUND

Atrial fibrillation is one of the most common complications of cardiac surgery. Beta blockers have been demonstrated to decrease the incidence of postoperative atrial fibrillation. Preliminary investigations reporting sotalol and atenolol to be effective in preventing postoperative atrial fibrillation are encouraging, but no studies have been conducted comparing both drugs.

METHODS

A total of 253 consecutive eligible patients (66 +/- 8 years; mean +/- standard deviation) scheduled to undergo cardiac surgery were enrolled in this study. Patients were randomized in a prospective open manner 1.5:1 to atenolol group (50 mg/daily; 153 patients) or sotalol group (80 mg twice daily; 100 patients).

RESULTS

Atrial fibrillation occurred in 44/253 patients (17.45%). A significant difference was found in the occurrence of atrial fibrillation in the atenolol group (34 patients, 22%) compared with those receiving sotalol (10 patients, 10%; p = 0.013). Therapeutic efficiency and efficacy was 12% and 54%, respectively. Stepwise logistic regression analysis revealed that age more than 68 years old (odds ratio = 2.72; 95% confidence interval [CI] = 1.37-5.41; p = 0.004), the use of beta-adrenergic agents (odds ratio = 2.74; 95% CI = 1.5-5; p = 0.001), and sotalol (odds ratio = 0.46; 95% CI = 0.23-0.95; p = 0.035) were independently associated with development of atrial fibrillation.

CONCLUSIONS

Oral low-dose sotalol provides a considerable reduction in the occurrence of atrial fibrillation. A selective approach based on clinical risk prediction should decrease the occurrence of atrial fibrillation after cardiac surgery.

Mortalidad del infarto de miocardio en el registro PRIMVAC. Factores pronósticos

BACKGROUND AND OBJECTIVE

The aim of this study was to determine the mortality due to acute myocardial infarction in the coronary units from Comunidad Valenciana (Spain) and the prognostic factors associated with a higher mortality.

PATIENTS AND METHOD

Demographic characteristics, coronary risk factors, electrocardiographic ischemic signs, complications and mortality of patients with acute myocardial infarction admitted in the coronary units were collected. The study period comprised January 1995-December 1999. Death incidence was measured during coronary unit's stay. Factors associated with poor prognosis were analyzed.

RESULTS

10.213 patients entered into the study. Mean age at admission was 65 12 years. 23.8% were females (76.2% males). Global mortality in coronary units was 13.3%. Independent variables associated with higher mortality were (p < 0.05): advanced age (OR=1.06 [1.05-1.06]), female sex (OR=1.45 [1.26-1.66]), diabetes mellitus (OR=1.53 [1.35-1.74]), previous myocardial infarction (OR=1.46 [1.23-1.70]), previous angor pectoris (OR=1.29 [1.13-1.49]) and Q-wave infarction (OR=1.23 [1.03-1.43]). Factors associated with lower mortality were: hypercholesterolemia (OR=0.76 [0.66-0.78]), smoking (OR=0.65 [0.57-0.74]) and thrombolysis (OR=0.85 [0.78-0.92]).

CONCLUSIONS

At present, in the reperfusion therapy era, acute myocardial infarction has a high mortality after coronary unit admission. Several clinical factors are associated with a worse prognosis.

[Acute renal failure in critically ill patients. A prospective epidemiological study]

AIMS

To determine factors which may predict mortality in patients admitted to intensive care unit who present acute renal failure.

METHODS

Prospective observational study of the patients admitted to a multidisciplinary intensive care unit over a year. The inclusion criteria were a creatinine plasmatic value > or = 2 mg/dl (177 micromol/l) or an increase (30% or higher) of its basal value on admittance.

RESULTS

One hundred and twenty-seven patients (age = 65.83 +/- 15.06 years; 38% male) with acute renal failure, were prospectively enrolled in the study (13% of intensive care unit admissions). The univariate analysis showed that hospital origin, acute tubular necrosis, late ARF, oliguria, maintained hypotension, sedation or coma, oncological disease and need of mechanical ventilation were significantly associated with mortality (p < 0.05). This association was also found for sepsis (OR: 41.5), multiorganic failure (OR: 3.58) and respiratory, cardiovascular or haematological failure according to the SOFA score. The multivariate analysis found that four clinical variables had an independent predictive value for mortality risk: acute tubular necrosis [OR: 4.57 (2.32-9.00)], use of vasoactive drugs [OR: 2.32 (1.22-4.40)], oliguria [OR: 2.15 (1.12-4.13)] and the acute renal failure starting during admission [OR: 2.06 (1.09-3.88)].

CONCLUSION

Data related to renal failure have worse prognosis than other demographic or clinical data in critically ill patients with acute renal failure. Multicentric studies with unified criteria are needed to analyse the most important prognostic factors.

[Prognostic factors in unstable angina with dynamic electrocardiographic changes. Value of fibrinogen]

INTRODUCTION AND OBJECTIVES

The prognosis of unstable angina varies between series depending on the inclusion criteria and management protocol used. The aim of this study was to analyze in-hospital events and their predictors in a homogeneous single-center series of patients with unstable angina.

MATERIAL AND METHODS

A total of 246 patients with the following inclusion criteria were studied: 1) resting anginal pain, 2) transient electrocardiographic changes during anginal pain, 3) normal CK-MB levels and 4) exclusion of postinfarction angina. All patients were treated with aspirin and enoxaparin (1 mg/kg/12 h). Coronary angiography was performed in the case of recurrent angina or ischemia in Bruce I-II stage during the predischarge effort stress test. The variables recorded were risk factors, history of ischemic heart disease, history of coronary surgery, ECG upon admission, and fibrinogen.

RESULTS

During the hospital stay the following events were recorded: 36% recurrent angina, 58% cardiac catheterization, and 5,7% major events (infarction or death). Multivariate analysis found recurrent angina to be more frequent in patients with a history of coronary bypass surgery (p = 0.004. OR = 22; CI 95%, 3-182), ST-segment changes (p = 0.01. OR = 4.7, CI 95%; 1.4-15.9) and higher fibrinogen (p = 0.002. OR = 1,4, CI 95%; 1.1-1.7). Fibrinogen was the only variable related to cardiac catheterization (p = 0,009. OR = 1.3. CI 95%, 1.1-1.6) and major events (p = 0.001. OR = 2.0. CI 95%, 1.4-3.1).

CONCLUSIONS

1) Unstable angina with electrocardiographic changes was associated to a high rate of in-hospital events. 2) Fibrinogen was related to any event, and previous by-pass surgery and ST changes were related to recurrent angina.

Transmission bottlenecks and the evolution of fitness in rapidly evolving RNA viruses

We explored the evolutionary importance of two factors in the adaptation of RNA viruses to their cellular hosts, size of viral inoculum used to initiate a new infection, and mode of transmission (horizontal versus vertical). Transmission bottlenecks should occur in natural populations of viruses and their profound effects on viral adaptation have been previously documented. However, the role of transmission mode has not received the same attention. Here we used a factorial experimental design to test the combined effects of inoculum (bottleneck) size and mode of transmission in evolution of vesicular stomatitis virus (VSV) in tissue culture, and compared our results to the predictions of a recent theoretical model. Our data were in accord with basic genetic principles concerning the balance between mutation, selection and genetic drift. In particular, attenuation of vertically transmitted viruses was a consequence of the random accumulation of deleterious mutations, whereas horizontally transmitted viruses experiencing similar bottlenecks did not suffer the same fitness losses because effective bottleneck size was actually determined by the number of host individuals. In addition, high levels of viral fitness in horizontally transmitted populations were explained by competition among viral variants.

Tracing the origin of the compensasome: evolutionary history of DEAH helicase and MYST acetyltransferase gene families

Dosage compensation in Drosophila is mediated by a complex of proteins and RNAs called the "compensasome." Two of the genes that encode proteins of the complex, maleless (mle) and males-absent-on-the-first (mof), respectively, belong to the DEAH helicase and MYST acetyltransferase gene families. We performed comprehensive phylogenetic and structural analyses to determine the evolutionary histories of these two gene families and thus to better understand the origin of the compensasome. All of the members of the DEAH and MYST families of the completely sequenced Saccharomyces cerevisiae and Caenorhabditis elegans genomes, as well as those so far (June 2000) found in Drosophila melanogaster (for which the euchromatic part of the genome has also been fully sequenced) and Homo sapiens, were analyzed. We describe a total of 39 DEAH helicases in these four species. Almost all of them can be grouped in just three main branches. The first branch includes the yeast PRP2, PRP16, PRP22, and PRP43 splicing factors and their orthologs in animal species. Each PRP gene has a single ortholog in metazoans. The second branch includes just four genes, found in yeast (Ecm16) and Drosophila (kurz) and their orthologs in humans and Caenorhabditis. The third branch includes (1) a single yeast gene (YLR419w); (2) six Drosophila genes, including maleless and spindle-E/homeless; (3) four human genes, among them the ortholog of maleless, which encodes RNA helicase A; and (4) three C. elegans genes, including orthologs of maleless and spindle-E. Thus, this branch has largely expanded in metazoans. We also show that, for the whole DEAH family, only MLE and its metazoan orthologs have acquired new protein domains since the fungi/animals split. We found a total of 17 MYST family proteins in the four analyzed species. We determined putative orthologs of mof in both C. elegans and H. sapiens, and we show that the most likely ortholog in yeast is the Sas2 gene. Moreover, a paralog of mof exists in Drosophila. All of these results, together with those found for a third member of the compensasome, msl-3, suggest that this complex emerged after the fungi/animals split and that it may be present in mammalian species. Both gene duplication and the acquisition of new protein modules may have played important roles in the origin of the compensasome.

[The RICVAL study. Acute myocardial infarct in the city of Valencia. Data on 1,124 patients during the first twelve months of the registry (December, 1993--November, 1994)]

BACKGROUND AND OBJECTIVES

Information on the management of acute myocardial infarction in Spain is still scarce. The Register of Acute Myocardial Infarction of Valencia City (RICVAL) was established to collect, in a prospectively and uniformly way, data of patients with acute myocardial infarctions discharged from Valencia coronary care units, in order to obtain updated information on the management of these patients. Data of the first twelve months of the register are presented.

METHODS

Using standardised variables, demographic, clinical, procedural and outcome data from patients with acute myocardial infarction were collected at the eight hospitals collaborating in the RICVAL, from 1 December 1993 to 30 November 1994.

RESULTS

The eight participating hospitals cover 1,665,720 people. During 12 months, 1,124 patients were discharged from the participating coronary care units. Mean age was 65.1 years and 23.9% were female. The case fatality rate was 16.9%. Left ventricular failure (Killip 2, 3 and 4) was present in 42%. Thrombolytic therapy was applied in 43.5% with a median time delay of 210 minutes from chest pain onset. The delay time in initiating thrombolysis was longer in the women and in the elderly.

CONCLUSION

Analysis of present data shows the feasibility of an acute myocardial infarction register in Valencia City. The RICVAL study will allow a better knowledge of demographic, clinical, procedural and outcome data in patients with myocardial infarction. The case fatality rate is still high when we consider that an acceptable level of thrombolytic therapy has been reached. The long delay time in initiating thrombolysis, particularly in the elderly and in the women, must be emphasized.

A comparative study of the incorporation of a 1,6-beta-glucan and an O-glycosylated protein epitope into the cell wall of Candida albicans

The topological distribution of two epitopes in the cell wall of Candida albicans, the kinetics of their incorporation into the regenerating protoplast wall, and the effect of different antibiotics upon their incorporation and localization have been studied. To do so, two monoclonal antibodies that react against an O-glycosylated mannoprotein (1B12) and against a 1,6-beta-glucan epitope (JRR1) were used. The results show that the JRR1 epitope is localized in an internal layer of the cell wall, in contrast to the 1B12 epitope, which is superficial, and that the incorporation of the JRR1 epitope into walls of regenerating protoplasts precedes that of the 1B12 epitope. The JRR1 epitope is normally found in the culture medium of control cells, but not in that of papulacandin-B-treated cells, and tunicamycin interferes with the incorporation of the 1B12 epitope into the cell walls. Finally, the results support the hypothesis that mannoproteins are not 1,6-beta-glycosylated before their secretion.

[Survival in patients with sick sinus syndrome and artificial pacemaker. Determining clinical factors]

INTRODUCTION AND OBJECTIVE

The hypothesis that ventricular pacing is the most important factor in the survival of patients with Sick Sinus Syndrome remains controversial. The aim of this report was to determine independent clinical variables to predict survival in paced SSS patients.

METHODS

Retrospective, nonrandomized study of 153 patients with a mean age of 69 +/- 11 years, who received an initial pacemaker for Sick Sinus Syndrome between 1980 and 1994: 65 physiologic pacing (32 dual chamber, 33 atrial) and 88 ventricular pacing mode. After a maximum follow up of 177 months (median 57 months) the end point was total mortality.

RESULTS

Total mortality was 21%. Using univariate analysis, single chamber ventricular pacing, age > or = 70 years and NYHA > or = 2, was associated with a higher risk for total mortality (4 times increased risk for ventricular pacing compared to other pacing modalities). Independent predictors using multivariate analysis were: 1) NYHA > or = 2 (p < 0.05). 2) Coronary artery disease (p < 0.01). 3) Chronic obstructive pulmonary disease (p < 0.05) and 4) Gender (p < 0.05).

CONCLUSIONS

Mortality in patients with the Sick Sinus Syndrome is strongly predicted by preimplant baseline clinical variables. Our data indicate that the role of ventricular pacing mode remains inconclusive. A large, randomized study is necessary to confirm these results.

Identification of glucan-mannoprotein complexes in the cell wall of Candida albicans using a monoclonal antibody that reacts with a (1,6)-beta-glucan epitope

The use of a novel monoclonal antibody (mAb) that reacts with (1,6)-beta-glucan has permitted the study of the different covalent linkages between glucan and mannoproteins in the cell wall of Candida albicans. The mAb JRR1 was originally raised by immunization with Zymolyase extracts from C. albicans cell walls, but it soon became apparent that it reacted with a (1,6)-beta-glucan epitope. By using this antibody, we show the existence of glucan-mannoprotein complexes between the (1,6)-beta-glucan epitope recognized by the antibody and cell wall mannoproteins. The topology of the (1,6)-beta-glucan in the cell wall of C. albicans has also been studied.

[The incidence and significance of late potentials in patients with aborted sudden death]

BACKGROUND

Reentrant ventricular tachycardia and fibrillation probably have different electrophysiological bases. Regional conduction delay during sinus rhythm seems to be greatest in patients with spontaneous sustained ventricular tachycardia than in patients with spontaneous sustained ventricular fibrillation. We investigated the prevalence and significance of late potentials in patients with documented VT or VF in the setting of coronary diseases and other organic heart diseases.

PATIENTS AND METHODS

Nineteen patients with a history of spontaneous sustained ventricular tachycardia (11 patients) or fibrillation (8 patients) were studied with signal-averaged ECG. All patients had been resuscitated of sudden cardiac death. All recordings were made in sinus rhythm in an antiarrhythmic free state following the recommendations of the Committee of the European Society of Cardiology for data acquisition and analysis of ventricular late potentials using Signal Averaged Electrocardiography. The relationship between this late potentials and tachyarrhythmia inducibility during electrophysiologic study were established.

RESULTS

Abnormal late potentials were found in 79% of patients with sudden cardiac death. Patients with spontaneous ventricular tachycardia had a longer ventricular activation time in sinus rhythm than did patients with spontaneous ventricular fibrillation, but this difference did not reach statistic significance. The only analysis of late potentials could not discern the mechanism of sudden cardiac death. However when sudden cardiac death was caused by a spontaneous ventricular tachycardia, a good correlation between abnormal late potentials and induced ventricular tachycardia by programmed stimulation was found. Quantitative indices of late potentials did not correlate with ventricular tachycardia cycle length.

CONCLUSIONS

1) We have found and elevated incidence of abnormal late potentials in patients with sudden cardiac death, and 2) only when the mechanism of sudden cardiac death was a spontaneous VT, we were able to correlate abnormal late potential with provoked ventricular tachycardia during electrophysiologic study.

Incorporation of specific wall proteins during yeast and mycelial protoplast regeneration in Candida albicans

The kinectics of incorporation of two precursor mannoproteins into the regenerating cell wall of Candida albicans protoplasts have been followed at 28 degrees C and 37 degrees C using two monoclonal antibodies specific for protein epitopes (MAb 1B12 and 4C12) as probes. Both molecules were secreted from the beginning of the regeneration process, and their incorporation was retarded significantly. Analysis of the secreted materials by Western immunoblotting with MAb 1B12 allowed the identification of two closely migrating bands at apparent Mr higher than 170 kDa and significant amounts of a highly polydisperse material of even greater molecular mass. Some of these mannoproteinaceous species carried both N- and O-glycosidically linked mannose residues, as deduced from their drop in apparent Mr when synthesized in the presence of tunicamycin and by their reactivity with Concanavalin A. Following secretion, the molecules reacting with MAb 1B12 were incorporated into the regenerating walls by covalent binding. Then, when the antigen molecules were solubilized from partially regenerated walls, their mobility differed when regeneration took place at 28 degrees C (blastoconidia) or 37 degrees C (mycelial cells).

Observations on variability of atrioventricular nodal conduction in man and the dual-pathway response

A study was made of nodal conduction times of atrial stimuli with fixed coupling intervals, in 23 patients divided into two groups according to their atrial stimulus test response: Group I (continuous AV node function curve; 17 cases) and Group II (dual AV node pathway; six cases). The stimulation protocol involved the delivery of 75 stimuli with a fixed coupling interval 20 ms greater than the effective refractory period (ERP) of the AV node (Group I) or fast pathway (Group II). The atrial coupling intervals (A1A2) and node conduction times (A2H2) were measured. An evaluation was made of the dispersion of intervals with range (R) and of the distribution of A2H2 times (X2 test). In both Groups, R (A2H2) was greater than R(A1A2) (P less than 0.05); R(A2H2) in Group II was greater than R(A2H2) in Group I (P less than 0.001). In Group I the distribution of A2H2 was non-normal in four cases and bimodal in five; in Group II the distribution was non-normal and bimodal in all cases. It is concluded that: (1) the AV node generates a dispersion in its conduction times in the vicinity of its ERP, although the nodal conduction curve is continuous; and (2) the so-called dual pathway may constitute an exaggeration of AV node response inhomogeneity.