Between allopatry and secondary contact: differentiation and hybridization among three sympatric Gentiana species in the Qinghai-Tibet Plateau.

BACKGROUND: Mountains of the world host a significant portion of all terrestrial biodiversity, and the region of the Qinghai-Tibet Plateau (QTP) stands as one of the most remarkable mountain regions on Earth.  Because many explosive radiations occurred there, the QTP is a natural laboratory which is ideal to investigate patterns and processes linked to speciation and diversification. Indeed, understanding how closely related and sympatric species diverged is vital to explore drivers fostering speciation, a topic only rarely investigated in the QTP. By combining genomic and environmental data, we explored the speciation process among three closely related and sympatric species, Gentiana hexaphylla, G. lawrencei and G. veitchiorum in the QTP region. RESULTS: Combining genome sizes and cytological data, our results showed that G. hexaphylla and G. veitchiorum are diploid, whereas G. lawrencei is tetraploid. Genetic clustering and phylogenetic reconstruction based on genomic SNPs indicated a clear divergence among the three species. Bayesian clustering, migrant, and D-statistic analyses all showed an obvious signature of hybridization among the three species, in particular between G. lawrencei and both G. hexaphylla and G. veitchiorum in almost all populations. Environmental variables related to precipitation and particularly temperature showed significant differences among the three gentians, and in fact a redundancy analysis confirmed that temperature and precipitation were the major climatic factors explaining the genetic differentiation among the three species. CONCLUSION: Our study suggested that ancient hybridization, polyploidization, geological isolation and the evolution of different climatic preferences were all likely to be involved in the divergence of the three Gentiana species, as may be the case for many other taxa in the QTP region.

[Study on the activity--heart rate prediction system for motion sensed rate responsive pacemakers].

Focusing on the heart rate control mode of acceleration sensor based rate responsive pacemakers, this paper implemented the design of activity--heart rate prediction system. Bluetooth module was used as communication means in activity--heart rate prediction system, and the slave computer was used to complete the acceleration signal acquisition and processing, map from acceleration signal to the pacing rate signal, and achieve real-time transmission of acceleration signal and heart rate signal. The master computer fulfilled real-time display and recording of acceleration signal and heart rate signal, moreover, it achieved control function to the slave computer algorithm through classification of 6 parameters. The results of verification experiment showed that there was a significant relation between mapping heart rate and actual heart rate using linear mapping algorithm (R2 = 0.787, P < 0.001).

Mechanisms of the acute ischemia-induced arrhythmogenesis--a simulation study.

The underlying ionic mechanisms of ischemic-induced arrhythmia were studied by the computer simulation method. To approximate the real situation, ischemic cells were simulated by considering the three major component conditions of acute ischemia (elevated extracellular K(+) concentration, acidosis and anoxia) at the level of ionic currents and ionic concentrations, and a round ischemic zone was introduced into a homogeneous healthy sheet to avoid sharp angle of the ischemic tissue. The constructed models were solved using the operator splitting and adaptive time step methods, and the perturbation finite difference (PFD) scheme was first used to integrate the partial differential equations (PDEs) in the model. The numerical experiments showed that the action potential durations (APDs) of ischemic cells did not exhibited rate adaptation characteristic, resulting in flattening of the APD restitution curve. With reduction of sodium channel availability and long recovery of excitability, refractory period of the ischemic tissue was significantly prolonged, and could no longer be considered as same as APD. Slope of the conduction velocity (CV) restitution curve increased both in normal and ischemic region when pacing cycle length (PCL) was short, and refractory period dispersion increased with shortening of PCL as well. Therefore, dynamic changes of CV and dispersion of refractory period rather than APD were suggested to be the fundamental mechanisms of arrhythmia in regional ischemic myocardium.

[Study of cellular electrophysiology based on Noble98 dynamic model of ventricular action potential].

On the basis of mammalian ventricular action potential model Noble98, and with the use of Runge-Kutta for solution, the Wenckebach periodicity phenomenon, the transmural heterogeneity of the ventricular myocardium and its rate dependence are studied. The results indicate that these inherent properties may, lead to temporal-space disorganized in the normal heart,and may become the underlying factors for arrhythmias. At the same time, in this study are established the basic methods for quantitative cellular electrophysiology which is essential for future studies on the mechanism of arrhythmia.

[Computer simulation study of the re-entry mechanisms in one-dimensional ischaemic myocardium].

Torsades de Pointes is a kind of severe ventricular arrhythmia. Myocardial ischaemia is one of the major causes leading to TdP. In this paper the mechanisms of the TdP were quantitatively studied under the condition of ischaemia based on the Noble98 dynamic model of the ventricular action potential. The study was conducted on one-dimensional homogeneous myocardium with the method of computer simulation. The models were firstly developed to simulate the lower excitability, extracellular accumulation of the K+ concentration or the decreased gap junctions in ischaemic myocardium. By separately reducing the Na+ conductance, increasing the extracellular K+ concentration or decreasing the conductance of the gap junctions enabled us to study the effect of each change in isolation. Then different degrees of ischaemic models were established to study their physiological features. The study showed that the conduction velocity became slower with the ischaemia aggravation, the action potential duration became shorter and the width of the vulnerable window obviously became larger than the normal conditions. The results illustrated that ischaemia was easily leading to unidirectional conduction block and resulted in re-entry and arrhythmias.

[Optical mapping of the membrane potential with voltage-sensitive dyes].

Optical mapping of the membrane potential with voltage-sensitive dyes is an advanced approach that involves in many theories such as molecular photonica, physiology and computer science. Compared with the conventional techniques of membrane patch-clamp and microelectrode, the optical mapping system can measure not only the changes of a single membrane potential from multiple sites simultaneously but also the conduction properties of the cell populations. So this technique provides an important method for studying the electrophysiology of the small cell, the tiny neurite and the cardiac arrhythmia, etc. Because this technique can also avoid the electromagnetic interferences, it uniquely provides an ideal means for studying the mechanisms such as cardiac defibrillation. In this paper the principles and the system structure of the optical mapping are introduced, its applications and future developments are also presented at the same time.

Computer simulation of the reentrant cardiac arrhythmias in ischemic myocardium.

Computer simulation was performed to determine how reentrant activity could occur due to the spatial heterogeneity in refractoriness induced by the regional ischemia. Two regional ischemic models were developed by decreasing the intracellular ATP concentration, reducing conductance of the inward Na+ current and increasing the extracellular K+ concentration on the two-dimensional sheet. Operator splitting method was used to integrate the models. The vulnerability to reentry was estimated from the timings of premature stimuli on the constructed models, which could result in unidirectionally propagating action potentials. Two kinds of sustained spiral waves and their Pseudo-Electroscardiograms were observed in numerical simulation. The results showed that the dispersion of refractory period increased with ischemic aggravation, and led to augment of the vulnerable window. A permature stimulation within the vulnerable window could easily induce spiral reentry. The Pseudo-Electrocardiograms of the spiral waves exhibited monomorphic tachycardiac waveforms. Thus, the spatial heterogeneity in refractoriness could be a substrate for reentrant ventricular tachyarrhythmias on the regional ischemic tissue.

[Mathematical model of cardiac action potential and its computer simulations].

Malignant arrhythmias and ventricular fibrillation are generally accepted as one of the major causes of death in cardiovascular diseases. Based on the H-H equations, the mathematical model of the cardiac cell action potential consists of the ion channels, pumps, exchangers and transporters that are closely connected with intra- and extra-cellular ion concentrations, the channel's conditions, nerve transductors and drugs. It can build the link between cell electrophysiology and clinical pathophysiology. By altering the cellular environments the computer simulating study on this kind of model can help us look into the electrophysiological changes of the cardiac tissue and even the whole heart and investigate the mechanisms of the cardiac arrhythmias as well. The components of the model and its computer simulating study are introduced in the paper.