The long-term goal of Dr. Duan's Laboratory of Cardiovascular Phenomics is to determine the molecular mechanisms for the functional role of ion channels in the cardiovascular system in the context of health and disease. Ion channels are membrane-spanning proteins which form pores for ion permeation and are the major catalysts of many biological functions. Activation of ion channels can produce significant effects on cardiac electrical activity (automaticity and action potential) and contractile function (excitation-contraction coupling). In addition, ion channels are important regulators of acidification of intracellular organelles, cell volume, proliferation, differentiation, and apoptosis. Ion channels interact with many partners and function as an integrated "ion channel module" or "channel protein complex". Under pathological conditions "ion channel modules" often undergo remodeling and provide substrates for cardiovascular disease such as cardiac rhythm and contraction disorders and hypertension. Therefore, the study of ion channels has important significance in the translational medicine for the prevention and treatment of cardiovascular diseases. Chloride (Cl-) channels in the cardiovascular system, including the PKA- and PKC-activated CFTR Cl- channels, the volume-regulated outwardly rectifying ClC-3 and inwardly rectifying ClC-2 Cl- channels, the Ca2+-activated TMEM16 (Bestrophin and CLAC) Cl- channels, represent new targets for therapeutic agents against heart diseases. To gain mechanistic insights into the functional role of these ion channels in the context of health and disease the Duan laboratory has successfully established several animal models for cardiac diseases and hypertension and has the capacity to study the phenome-genome-proteome relationship and molecular mechanisms for cardiovascular disease at multiple levels of the whole-animal, the isolated organ, the tissue, the cell, and the molecule. The technology platforms used in the Duan laboratory include patch-clamp, molecular biology, genetics, genomics, proteomics, conditional systems for gene targeting and addition, isolated heart perfusion system, echocardiography, and telemetry system.
Within the past decade, deep brain stimulation that delivers microsecond duration electric pulses to specific brain regions via surgically implanted electrodes has become an established treatment for movement disorders (e.g., Parkinson's disease, tremor and dystonia) in patients who either do not respond to drug treatment or else experience unacceptable drug side effects. Other potential clinical applications of deep brain stimulation include treatment of epilepsy, pain and neurological disorders such as depression. My research builds on the growing clinical acceptance of electric stimulation for neuromodulation by focusing on a new type of electric stimulus, high intensity (> 1 megavolt-per-meter), nanosecond duration electric pulses, as an emerging technology for altering neural cell excitability. In a highly interdisciplinary collaborative effort, I have been exploring the effectiveness of nanoelectropulses less than 10 ns in duration for evoking neurosecretion. Using adrenal chromaffin cells as a model of neural-type cells, we found that a 5 ns, 5 megavolt-per-meter electric pulse causes activation of voltage-gated calcium channels, which leads to calcium influx and the exocytotic release of the catecholamines epinephrine and norepinephrine. This secretory response not only mimics the stimulation of catecholamine release evoked in vivo by the neurotransmitter acetylcholine but also occurs in the absence of deleterious cellular effects. We are currently addressing how such an ultra-short electric stimulus is capable of evoking neurosecretion. Preliminary evidence points to a novel mechanism, namely reversible membrane depolarization that depends on the transient formation of sodium-conducting nanopores in the plasma membrane lipid bilayer. That is, a nanoelectropulse causes the plasma membrane lipid bilayer to assume a role typically ascribed to protein ion channels, ion conductance that leads to membrane depolarization. The research spans the disciplines of neurobiology, electrophysiology, biophysics, physics and engineering where experimental approaches, such as patch clamp and fluorescence imaging for monitoring cellular responses, are integrated with electro-physical computational approaches, in particular cell modeling and molecular dynamics simulations that can elucidate on a nanosecond time scale how the electric field interacts with the plasma membrane and how the membrane behaves under the influence of the electric field. Another major goal of the research is to assess further the potential use of nanoelectropulses for modulating neurosecretion by establishing patterns of pulse delivery (pulse number versus pulse rate) that are effective for evoking reproducible effects on catecholamine release without causing adverse effects. The hope is that the research will be critical to the future development of an electrostimulation approach that is less invasive (does not require surgical implantation of electrodes) than the one currently used for neuromodulation, and that it will also result in new strategies for modulating the activity of other types of excitable cells.