Speciation within the Anopheles gambiae complex: high-throughput whole genome sequencing reveals evidence of a putative new cryptic taxon in 'far-west' Africa.

The two main Afrotropical malaria vectors - Anopheles coluzzii and An. gambiae - are genetically distinct and reproductively isolated across West Africa. However, populations at the western extreme of their range are assigned as "intermediate" between the two species by whole genome sequence (WGS) data, and as hybrid forms by conventional molecular diagnostics. By exploiting WGS data from 1,190 specimens collected across west Africa via the Anopheles gambiae 1000 Genomes network, we identify a novel putative taxon in the far-west (provisionally named Bissau molecular form), which did not arise by admixture but rather originated at the same time as the split between An. coluzzii and An. gambiae. Intriguingly, these populations lack insecticide resistance mechanisms commonly observed in the two main species. These findings lead to a change of perspective on malaria vector species in the far-west region with potential for epidemiological implications, and a new challenge for genetic-based mosquito control approaches.

Are fur farms a potential source of persistent organic pollutants or mercury to nearby freshwater ecosystems?

Farming of carnivorous animals for pelts potentially contaminates nearby ecosystems because animal feed and waste may contain persistent organic pollutants (POPs) and metals. Mink farms in Nova Scotia (NS), Canada, provide mink with feed partially composed of marine fish meal. To test whether mink farms potentially contribute contaminants to nearby lakes, we quantified organochlorine pesticides (OCP), polychlorinated biphenyls (PCB), and total mercury (THg) in mink/aquaculture feed, waste, and sediment collected from 14 lakes within rural southwest NS where mink farms are abundant and have operated for decades. Mercury, PCBs, dichlorodiphenyltrichloroethane (DDT), hexachlorocyclohexane (HCH), and dieldrin were present in mink/aquaculture feed and mink waste, indicating they are potential contaminant sources. Lakes with mink farms in their catchment exhibited significantly higher THgflux than lakes downstream of mink farming activity and reference lakes (p < 0.0001) after the intensification of mink farming in 1980, indicating mink farming activity is likely associated with increased lacustrine THgflux. Sedimentary Æ©PCBflux was elevated in lakes with mink farms in their catchments, suggesting possible PCB contributions from mink farming, local agriculture, and atmospheric deposition. Elevated Æ©DDT in lakes near mink farms relative to reference lakes suggests a possible enrichment related to mink farming, although mixed land use and historical DDT usage related to forestry in the region complicates DDT source attribution. Maximum dieldrinflux and HCHflux in lake sediment occurred coeval with peak worldwide usage in the 1970s and are unlikely to be associated with local mink farming. Lakes with mink farming activities in their catchments were associated with increased THgflux, Æ©PCBflux, and possibly Æ©DDTflux, suggesting a possible connection between marine fish meal, fur farms, and aquatic ecosystems in NS.

Geochemical and sulfate isotopic evolution of flowback and produced waters reveals water-rock interactions following hydraulic fracturing of a tight hydrocarbon reservoir.

Although multistage hydraulic fracturing is routinely performed for the extraction of hydrocarbon resources from low permeability reservoirs, the downhole geochemical processes linked to the interaction of fracturing fluids with formation brine and reservoir mineralogy remain poorly understood. We present a geochemical dataset of flowback and produced water samples from a hydraulically fractured reservoir in the Montney Formation, Canada, analyzed for major and trace elements and stable isotopes. The dataset consists in 25 samples of flowback and produced waters from a single well, as well as produced water samples from 16 other different producing wells collected in the same field. Additionally, persulfate breaker samples as well as anhydrite and pyrite from cores were also analyzed. The objectives of this study were to understand the geochemical interactions between formation and fracturing fluids and their consequences in the context of tight gas exploitation. The analysis of this dataset allowed for a comprehensive understanding of the coupled downhole geochemical processes, linked in particular to the action of the oxidative breaker. Flowback fluid chemistries were determined to be the result of mixing of formation brine with the hydraulic fracturing fluids as well as coupled geochemical reactions with the reservoir rock such as dissolution of anhydrite and dolomite; pyrite and organic matter oxidation; and calcite, barite, celestite, iron oxides and possibly calcium sulfate scaling. In particular, excess sulfate in the collected samples was found to be mainly derived from anhydrite dissolution, and not from persulfate breaker or pyrite oxidation. The release of heavy metals from the oxidation activity of the breaker was detectable but concentrations of heavy metals in produced fluids remained below the World Health Organization guidelines for drinking water and are therefore of no concern. This is due in part to the co-precipitation of heavy metals with iron oxides and possibly sulfate minerals.

Application of micro-FTIR mapping and SEM to study compositional heterogeneity of siltstones: Example from the Late Devonian-Early Mississippian Middle Bakken Member.

This paper explores the applicability of micro-FTIR mapping to study heterogeneity of organic matter-lean siltstones. Closely spaced samples of Late Devonian dolomitic siltstones of the Middle Bakken Member were analysed with micro-FTIR, powder X-ray diffraction, and scanning electron microscopy (SEM) to explore the distribution and chemical properties of organic matter (OM), muscovite/feldspar/clay group, carbonates, and quartz, and their influence on porosity and permeability of these rocks. Our results show that quartz is the dominant component of the samples, and the main mineralogical differences between the samples are reflected in the abundance of carbonate minerals. Organic matter content is usually far below 1 wt. % and dominantly represented by terrestrially derived vitrinite and inertinite. Micro-FTIR mapping demonstrates that the more spatially connected quartz and muscovite/feldspar/clays become, the larger permeability in the rock develops, and these correlations are especially strong for planes parallel to bedding. In contrast, carbonate connectivity shows a strong negative correlation with permeability. No correlations between connectivity of components and porosity have been detected. These observations suggest that micro-FTIR not only can document compositional heterogeneity of siltstones, but also has potential to help understanding their permeability systems.

Treatment outcomes for eosinophilic esophagitis in children with esophageal atresia.

Eosinophilic esophagitis (EoE) has been reported to be more prevalent in patients with esophageal atresia/tracheoesophageal fistula (EA-TEF). To date, there is limited data on the management of EoE in this group of patients. The aim of this study is to evaluate the treatment outcomes of EoE in children with EA-TEF. A retrospective chart review was performed on all EA-TEF children who were diagnosed with and treated for EoE between January 2000 and September 2013 at the Sydney Children's Hospital. Data collected included details of the patient's treatment, post-treatment endoscopy, symptoms and nutrition. Twenty patients were included in the study. Median age at diagnosis was 26 months (8-103 months), and median time from diagnosis to last follow-up was 23 months (2-132 months). Patients were treated with budesonide slurry, swallowed fluticasone, elimination diet alone or in combination. All patients were on proton pump inhibitors at time of diagnosis of EoE which was continued. Six out of seven patients who had furrowing/exudate in endoscopy at diagnosis had complete resolution at a median follow-up period of 26 months (P = 0.031). Median peak intraepithelial eosinophil count reduced significantly from 30/high-powered field (HPF) (19-80/HPF) to 8/HPF (0-85/HPF) (median time for improvement = 24 months) (P = 0.015). There was a significant reduction in symptoms of dysphagia and reflux post-treatment (P < 0.001). Prevalence of strictures significantly decreased (P = 0.016), as did need for dilatations (P = 0.004). In four out of six patients with gastrostomies at baseline, the feeding improved on treatment of EoE and the gastrostomy could be closed. There was also a nonsignificant trend towards improvement in weight and height 'z scores' of the patients. Treatment of EoE in children with EA-TEF was found to significantly reduce intraepithelial eosinophil count, symptoms, strictures and need for dilatations.

Generativity, hierarchical action and recursion in the technology of the Acheulean to Middle Palaeolithic transition: a perspective from Patpara, the Son Valley, India.

The Acheulean to Middle Palaeolithic transition is one of the most important technological changes that occurs over the course of human evolution. Here we examine stone artefact assemblages from Patpara and two other excavated sites in the Middle Son Valley, India, which show a mosaic of attributes associated with Acheulean and Middle Palaeolithic industries. The bifaces from these sites are very refined and generally small, but also highly variable in size. A strong relationship between flake scar density and biface size indicates extensive differential resharpening. There are relatively low proportions of bifaces at these sites, with more emphasis on small flake tools struck from recurrent Levallois cores. The eventual demise of large bifaces may be attributed to the curation of small prepared cores from which sharper, or more task-specific flakes were struck. Levallois technology appears to have arisen out of adapting aspects of handaxe knapping, including shaping of surfaces, the utilization of two inter-dependent surfaces, and the striking of invasive thinning flakes. The generativity, hierarchical organization of action, and recursion evident in recurrent Levallois technology may be attributed to improvements in working memory.

Fat, oil and grease deposits in sewers: characterisation of deposits and formation mechanisms.

Fat, oil and grease deposits (FOG) in sewers are a major problem and can cause sewer overflows, resulting in environmental damage and health risks. Often simplistically portrayed as cooling of fats, recent research has suggested that saponification may be involved in FOG formation. However there are still questions about the mechanisms effecting transformations in sewers and the role and source of metal cations involved in saponification. This study characterises FOG deposits from pumping stations, sewers and sewage works from different water hardness zones across the UK. The sites all had previous problems with FOG and most catchments contained catering and food preparation establishments. The FOG deposits were highly variable with moisture content ranging from 15 to 95% and oil content from 0 to 548 mg/g. Generally the pumping stations had lower moisture content and higher fat content, followed by the sewers then the sewage works. The water in contact with the FOG had high levels of oil (mean of about 800 mg/L) and this may indicate poor kitchen FOG management practices. FOG fatty acid profiles showed a transformation from unsaturated to saturated forms compared to typical cooking oils. This seems to relate to ageing in the sewer network or the mechanism of formation, as samples from pumping stations had higher proportions of C18:1 compared to C16. This may be due to microbial transformations by bacteria such as Clostridium sp. in a similar process to adipocere formation. There was an association between water hardness and increased Ca levels in FOG along with harder deposits and higher melting points. A link between FOG properties and water hardness has not been previously reported for field samples. This may also be due to microbial processes, such as biocalcification. By developing the understanding of these mechanisms it may be possible to more effectively control FOG deposits, especially when combined with promotion of behavioural change.

Effects of cocaine and its major metabolites on the HERG-encoded potassium channel.

Cocaine abuse has been reported to result in QT prolongation in humans; however, the mechanisms underlying this effect are still poorly understood. In this study we compared the direct effects of cocaine and its major metabolites in human embryonic kidney 293 cells stably transfected with human ether-a-go-go-related gene (HERG). Cocaine blocked HERG-encoded potassium channels with an IC50 of 4.4 +/- 1.1 microM (22 degrees C). Cocaethylene (a metabolite formed in the presence of ethanol) had a significantly lower IC50 of 1.2 +/- 1.1 microM (P < 0.0001), and cocaine's primary pyrolysis metabolite methylecgonidine blocked HERG with a higher IC50 of 171.7 +/- 1.2 microM. In contrast, 1 mM ecgonine methylester or benzoylecgonine produced only a minimal block (21 +/- 4 and 15 +/- 8%, respectively). Blockade of HERG by cocaine, cocaethylene, and methylecgonidine increased significantly over the voltage range where HERG activates, but became constant at voltages where HERG activation was maximal, indicating that all three drugs block open channels, but by a mechanism that is not highly sensitive to voltage per se. Cocaine and cocaethylene also significantly slowed the time course of deactivation at -60 mV, an effect consistent with open channel block. We conclude that cocaethylene is slightly more potent than cocaine as a blocker of HERG, whereas methylecgonidine has much lower potency, and both benzoylecgonine and ecgonine methyl ester are essentially inactive at clinically relevant concentrations.

Quinidine interactions with human atrial potassium channels: developmental aspects.

Clinical studies have suggested that quinidine is less effective when used for the treatment of atrial arrhythmias in pediatric patients compared with its clinical effectiveness in the adult patient population. Age-related changes in the cardiac actions of quinidine on action potential duration and interaction with potassium channels in several mammalian species also have been reported. We investigated the effects of postnatal development on quinidine's interaction with major repolarizing currents (Ito, IKur, Ins, and IK1) in human atrial myocytes, using the whole-cell configuration of the voltage-clamp technique. Our results indicate that there are age-related changes in both the IC50 for quinidine blockade of Ito, as well as the mechanism of quinidine unblocking. In contrast, quinidine was found to inhibit both adult and pediatric IK1 and IKur in an age-independent manner, whereas the nonselective cation current (Ins), which contributes to the sustained outward current (Isus), was insensitive to quinidine. The results from this study help to clarify the electrophysiological mechanism by which quinidine elicits its antiarrhythmic effect in the pediatric and adult human population.

Hematological complications of Gaucher's disease in pregnancy.

A case is presented of a 31-year-old Filipino female, gravida 5 para 2, at 38 weeks plus 5 days gestation, with known type I Gaucher's disease who underwent repeat cesarean delivery. After cesarean delivery, the patient developed disseminated intravascular coagulation and required transfusion of eight 6-packs of platelets, 6 units of fresh frozen plasma, two 10-packs of cryoprecipitate, and 6 units of packed red blood cells. Pregnancy is generally well tolerated in patients with type I Gaucher's disease, an autosomal recessive lysosomal storage disorder in which lipid deposits accumulate in the liver, spleen, and bone marrow. Hemorrhagic problems secondary to severe thrombocytopenia may develop postpartum in pregnancies complicated by Gaucher's disease, requiring significant support with blood and blood products.

L-type calcium current in pediatric and adult human atrial myocytes: evidence for developmental changes in channel inactivation.

Animal studies have documented the presence of marked, species-dependent, developmental changes in the properties of the L-type calcium current in cardiac myocytes. In an effort to understand the postnatal changes which occur in the calcium current in human heart, we characterized the calcium current in atrial myocytes isolated from 17 pediatric and older children (ages 3 d to 14 y) and 12 adult (ages 43-79 y) human hearts using the whole-cell patch clamp technique. In contrast to animal models, we found no evidence for age-related changes in calcium current density, steady-state inactivation, or kinetics of recovery from inactivation, suggesting that, in human atrium, calcium channels are in many aspects functionally mature at the time of birth. However, statistically significant differences were found in the kinetics of calcium current inactivation, with calcium current measured in cells isolated from pediatric human atria inactivating approximately 2-fold faster than cells isolated from adult hearts. These results suggest a possible role for age-related changes in calcium current inactivation in the shortened action potential duration observed in pediatric compared with adult human atrium.

The rat MHC haplotype RT1c expresses two classical class I molecules.

Cloning and characterization of classical MHC class I coding sequences of the laboratory rat Rattus norvegicus has been reported so far for only four haplotypes, RT1a, RT1(1), RT1n, and RT1u. In all four cases, only one RT1.A classical class I molecule was found. Here we report that, in contrast, the RT1c haplotype expresses two different classical class I molecules. Using recombinant rat strains, we find that allotypic serologic determinants carried by the two molecules map to the RT1.A region, and so we have named them RT1.A1c and RT1.A2c. Multiple clones of functional cDNAs for each of these two molecules were isolated using a recently developed PCR-based expression-cloning method. Using a panel of 20 RT1.Ac-reactive mAb, we find that six recognize RT1.A1c, seven recognize RT1.A2c, and seven recognize both. We also show that both molecules are recognized and distinguished by primary alloreactive cytotoxic T lymphocytes, and that they correspond to identifiable and distinct molecular species in cells that express RT1c naturally. These data all concur to demonstrate that the RT1.Ac region carries two different loci, each of which encodes a functional classical class I molecule.

Analysis of the ionic basis for cocaine's biphasic effect on action potential duration in guinea-pig ventricular myocytes.

The effects of cocaine on the duration of the cardiac action potential were investigated in isolated guinea-pig ventricular myocytes at 37 degrees C. Following a 10-min exposure of cells to 3 microM cocaine, APD90 increased significantly by +22 +/- 5% (n = 6). In contrast, following a ten minute exposure to 30 or 100 microM cocaine, APD90 was reduced by -24 +/- 6% (n = 5) and -53 +/- 2% (n = 8), respectively. The ionic basis for cocaine's effects on the APD was investigated using the whole cell voltage-clamp technique at 37 degrees C. Cocaine produced a concentration-dependent reduction in the amplitude of IK tail currents with an estimated IC50 of 4 microM. The kinetics and voltage dependence of the cocaine-sensitive current indicate that cocaine selectively blocks a current identical to the E-4031 sensitive current IKr. No significant reduction of the slow component of IK (IKs) was observed during exposure to 30 or 100 microM cocaine. High (30 and 100 microM) concentrations of cocaine also produced a significant reduction of both the L-type calcium current and the TTX-sensitive plateau current. Pre-treatment of cells with 10 microM TTX also converted the APD-shortening effect of 30 microM cocaine to one of APD-prolonging. This implies that cocaine block of a TTX-sensitive window current contributes to the APD-shortening effects produced by high concentrations of cocaine. We conclude that: (1) cocaine produces a biphasic concentration-dependent effect on repolarization in guinea-pig ventricular myocytes; and (2) this biphasic effect on repolarization results from differences in the sensitivity of inward and outward currents to the blocking effects of cocaine.

Description of a nonselective cation current in human atrium.

Ion currents were examined in isolated human atrial myocytes by using the whole-cell patch-clamp technique. When currents were recorded with a K(+)-containing pipette solution, depolarizing voltage pulses elicited a rapidly activating outward current that decayed to an apparent steady state. Exposure of cells to 10 mmol/L 4-aminopyridine markedly reduced current amplitude; however, a rapidly activating current that was approximately 30% of the steady state current amplitude remained. When pipette K+ was replaced with Cs+, a similar rapidly activating current that reversed polarity at approximately 0 mV was recorded. This current was seen in 100% of the cells tested from 17 different hearts (n = 142), and its amplitude was approximately 40% of the amplitude of the steady state current recorded in the presence of pipette K+. The current amplitude was not significantly different in cells isolated from adult (6.31 +/- 1.35 pA/pF, n = 8) and pediatric (5.54 +/- 1.04 pA/pF, n = 9) hearts. Studies designed to determine the charge-carrying species indicated that changes in bath Cl- concentration had no effect on either the amplitude or the reversal potential of this current, whereas removal of pipette Cs+ and bath Na+ dramatically reduced this current. In addition, this current was not modulated by either isoproterenol (1 mumol/L, 22 degrees C) or cell swelling. This study provides the first description of a nonselective cation current in human atrial myocytes, which may play an important role in repolarization in human atria.

The pH dependence of cocaine interaction with cardiac sodium channels.

Previous in vitro and in vivo studies have provided evidence implicating cocaine block of cardiac sodium channels as a putative mechanism for cocaine-induced arrhythmias and sudden death. Cocaine also has been shown to cause seizures which can result in respiratory and/or metabolic acidosis. In this study we investigated how changes in both internal pH (pHi) and external pH (pHo) over the range of 6.6 to 9.2 modify the sodium channel blocking properties of cocaine in isolated guinea pig ventricular myocytes by using the whole-cell variant of the patch clamp technique. Use-dependent block produced by a train of 1-sec pulses to -20 mV was not affected by changes in pHi, but both the amplitude and time constant for approaching steady-state block were significantly affected by changes in pHo. Characterization of the time course of cocaine binding during a depolarizing pulse indicated that the kinetics of drug interaction with inactivated channels were independent of pHi, but were significantly affected by changes in pHo. The rate of recovery from channel block at a holding potential of -140 mV also was independent of pHi, but strongly dependent on pHo, with the unblocking time constant decreasing exponentially as pHo was increased. The results of this study indicate that cocaine's effect on cardiac sodium channels can be modulated significantly by changes in pHo, and provide further support for previously poorly tested assumptions of the modulated receptor hypothesis.

Comparison of Ito in young and adult human atrial myocytes: evidence for developmental changes.

In an effort to understand the ionic basis for the developmental changes that have been reported to occur in the configuration of the human atrial action potential, we characterized the transient outward current (Ito) and the inward rectifier current in atrial myocytes isolated from 20 young (ages 1 day-2.5 yr) and 8 adult (11-68 yr) human hearts using the whole cell patch-clamp technique. We found evidence for statistically significant (P < 0.05) age-related changes in the Ito, including 1) the presence of an Ito in only 67% of the cells isolated from young hearts vs. 100% of the cells isolated from adult hearts, 2) an almost twofold increase in the current density of Ito in adult cells vs. young cells, and 3) recovery kinetics that are approximately twofold slower in young myocytes relative to adult myocytes. In contrast, there were no age-related changes found in the current density of the inward rectifier current or the sustained current measured after the decay of Ito. These results suggest important current-dependent changes that occur with age in human atria.

Cocaethylene, a metabolite of cocaine and ethanol, is a potent blocker of cardiac sodium channels.

Cocaethylene is an active metabolite of cocaine believed to play a causative role in the increased incidence of sudden death in individuals who coadminister ethanol with cocaine. However, the direct effects of cocaethylene on the heart have not been well defined. In this study, we defined the effects of cocaethylene on the cardiac Na current (INa) in guinea pig ventricular myocytes at 16 degrees C using the whole-cell patch-clamp method. Cocaethylene (10-50 microM) produced both a significant tonic block and a rate-dependent block of INa at cycle lengths between 2 and 0.2 sec. Cocaethylene produced a significantly greater tonic block than cocaine at a concentration of 50 microM and produced a significantly greater use-dependent block over a 5-fold range of drug concentrations (10-50 microM) and cycle lengths (0.2-1.0 sec). Analysis of channel-blocking characteristics revealed that cocaethylene had a significantly higher affinity for inactivated channels (Kdi = 5.1 +/- 0.6 microM, n = 15) compared with cocaine (Kdi = 7.9 +/- 0.5 microM, n = 10) (P < .01) and that cocaethylene produced a significantly greater hyperpolarizing shift of the steady-state INa inactivation curve (P < .05). Cocaethylene also had a significantly longer time constant for recovery from channel block at -140 mV (12.24 +/- 0.88 sec, n = 16) compared with cocaine (8.33 +/- 0.56 sec, n = 14) (P < .01).(ABSTRACT TRUNCATED AT 250 WORDS)

Sequence of ovine Ig gamma 2 constant region heavy chain cDNA and molecular modelling of ruminant IgG isotypes.

Ovine mesenteric lymph node mRNA was used for PCR amplification of DNA coding for immunoglobulin gamma 1 and gamma 2 heavy chain constant regions. Primers complementary to regions of CH1 conserved between ruminants were used for upstream priming, with downstream priming on the poly-A segment. PCR products of the appropriate length were cloned and gamma positive clones selected with a CH1 conserved-region probe. Of these, gamma 1 clones were positively selected and gamma 2 clones negatively selected with a gamma 1 hinge-specific probe. Ovine gamma 2 cDNA has 93% identity of nucleotides with ovine gamma 1. Both ovine gamma 1 and gamma 2 CH1 domains encoded two consecutive cysteine residues (Cys-127, -128, Kabat numbering), an arrangement which is deduced to form a pair of disulphide bridges, one to the L chain and one as an intra-chain bridge to the uppermost Cys of the hinge, as in rabbit and goat IgG. The majority of the differences between the isotypes occur in the hinge region and an evolutionary pattern for ruminant IgG hinges can now be identified. IgG1 isotypes are typical, with hinges containing the C-terminal Cys-Pro motif, but deletion and replacement of nucleotides (in the ancestral gene) of ruminant gamma 2 has shortened the IgG2 hinge, removing the Cys-Pro motif and the consensus high affinity Fc gamma RI receptor motif at the start of CH2. An N-terminal glycosylation site and the peptide motif for complement C1q binding are present in CH2 of both isotypes. The hinge regions of gamma 1 and gamma 2 and predicted structures for ovine IgG1 and IgG2 have been modelled. Close apposition of Fab and Fc in IgG2 produces steric hindrance at the normally accessible Fab/hinge/Fc interface; the structural differences between the ruminant isotypes form a basis for understanding some of the differences in their effector properties.

Electrophysiological effects of high cocaine concentrations on intact canine heart. Evidence for modulation by both heart rate and autonomic nervous system.

BACKGROUND: Previous clinical reports have suggested that cocaine intoxication may produce severe ventricular arrhythmias due to a direct effect on the heart. However, the effects of high plasma levels of cocaine on the electrophysiology of the heart have not been well characterized and remain poorly understood. METHODS AND RESULTS: The purpose of this study was to characterize the electrophysiological effects of high doses of cocaine on the in situ dog heart. In dogs anesthetized with morphine and alpha-chloralose, cocaine (2-11 micrograms/mL) increased both atrial and ventricular refractory periods and produced rate-dependent increases in atrial, atrioventricular, His-Purkinje, and ventricular conduction intervals. The time constant for the onset of cocaine's conduction slowing effect following a reduction in pacing cycle length from 400 to 260 msec was approximately two beats, and the time constant for diastolic recovery from conduction slowing was approximately 200 msec, which are similar to values reported for several class Ib antiarrhythmic drugs. Cocaine produced a rate-dependent increase in QT interval that was greatest at high heart rates yet produced no change in the ST (QT-QRS) interval. This suggests that high plasma levels of cocaine delay repolarization primarily via slowing of conduction. Cocaine's effects on both atrioventricular and intraventricular conduction were significantly larger in autonomically blocked than in autonomically intact animals. CONCLUSIONS: We conclude that high plasma levels of cocaine, similar to those reported in autopsy reports following fatal cocaine overdose in humans, produce significant rate-dependent conduction slowing effects on atrial, atrioventricular, and ventricular conduction in the in situ heart. These rate-dependent effects are intensified following autonomic blockade.