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We developed a two-dimensional model of transport-dependent intracellular calcium signaling in endothelial cells (ECs). Our purpose was to evaluate the effects of spatial colocalization of endothelial nitric oxide synthase (eNOS) and capacitative calcium entry (CCE) channels in caveolae on eNOS activation in response to ATP. Caveolae are specialized microdomains of the plasma membrane that contain a variety of signaling molecules to optimize their interactions and regulate their activity. In ECs, these molecules include CCE channels and eNOS. To achieve a quantitative understanding of the mechanisms of microdomain calcium signaling and the preferential sensitivity of eNOS to calcium entering the cell through CCE channels, we constructed a mathematical model incorporating the cell morphology and cellular physiological processes. The model predicts that the spatial segregation of calcium channels in ECs can create transport-dependent sharp gradients in calcium concentration within the cell. The calcium concentration gradient is affected by channel density and cell geometry. This transport-dependent calcium signaling specificity effect is enhanced in ECs by increasing the spatial segregation of the caveolar signaling domains. Our simulation significantly advances the understanding of how [Ca.sup.2+], despite its many potential actions, can mediate selective activation of signaling pathways. We show that diffusion-limited calcium transport allows functional compartmentalization of signaling pathways based on the spatial arrangements of [Ca.sup.2+] sources and targets. capacitative calcium entry; caveolae; endothelial cells: endothelial nitric oxide synthase; mathematical model

The drug-eluting stent's increasingly frequent occurrence late stage thrombosis have created a need for new strategies for intervention in coronary artery disease. This paper demonstrates further development of our minimally invasive, targeted drug delivery system that uses induced magnetism to administer repeatable and patient specific dosages of therapeutic agents to specific sites in the human body. Our first aim is the use of magnetizable stents for the prevention and treatment of coronary restenosis; however, future applications include the targeting of tumors, vascular defects, and other localized pathologies. Future doses can be administered to the same site by intravenous injection. This implant-based drug delivery system functions by placement of a weakly magnetizable stent or implant at precise locations in the cardiovascular system, followed by the delivery of magnetically susceptible drug carriers. The stents are capable of applying high local magnetic field gradients within the body, while only exposing the body to a modest external field. The local gradients created within the blood vessel create the forces needed to attract and hold drug-containing magnetic nanoparticles at the implant site. Once these particles are captured, they are capable of delivering therapeutic agents such as antineoplastics, radioactivity, or biological cells. Index Terms--Magnetic drug delivery, magnetic separation cardiovascular disease, stents.

A method is described for the manufacture of a microelectrode array for chronic, multichannel, single neuron recording. The ceramic-based, multisite electrode array has four recording sites patterned onto a ceramic shaft the size of a single typical microwire electrode. The sites and connecting wires are applied to the ceramic substrate using a reverse photolithographic procedure. Recording sites (22 x 80 [micro]m) are separated by 200 (micro)m along the shaft. A layer of alumina insulation is applied over the whole array (exclusive of recording sites) by ion-beam assisted deposition. These arrays were capable of recording single neuron activity from each of their recording sites for at least three weeks during chronic implantation in the somatosensory cortex of rats, and several sites had recordings that lasted for more than 8 weeks. The vertical arrangement of the recording sites on these electrodes is ideal for simultaneously recording across the different layers of brain areas such as the cerebral cortex and hippocampus in chronic preparations. Index Terms--Chronic implant, cortical histology, microelectrode array, multiple-single neuron recording, neural recording.

The capability to deliver high effective dosages to specific sites in the human body has become the holy grail of drug delivery research. Drugs with proven effectiveness under in vitro investigation often reach a major roadblock under in vivo testing due to a lack of an effective delivery strategy. In addition, many clinical scenarios require delivery of agents that are therapeutic at the desired delivery point, but otherwise systemically toxic. We propose a method for targeted drug delivery by applying uniform magnetic fields to an injected superparamagnetic colloidal fluid carrying a drug. The experimental and theoretical models presented give insight into the use of magnetic microspheres for site-specific delivery of therapeutic agents and blood flow occlusion for embolotherapy. Index Terms--Embolotherapy, magnetic particles, magnetic targeting, targeted drug delivery.

Abstract: Objectives: The effect of NO on smooth muscle cell contractility is crucial in regulating vascular tone, blood flow, and O2 delivery. Quantitative predictions for interactions between the NO production rate and the myogenic response for microcirculatory blood vessels are lacking. Methods: We developed a computational model of a branching microcirculatory network with four representative classes of resistance vessels to predict the effect of endothelium‐derived NO on the microvascular pressure‐flow response. Our model links vessel scale biotransport simulations of NO and O2 delivery to a mechanistic model of autoregulation and myogenic tone in a simplified microcirculatory network. Results: The model predicts that smooth muscle cell NO bioavailability significantly contributes to resting vascular tone of resistance vessels. Deficiencies in NO seen during hypoxia or ischemia lead to a decreased vessel diameter for all classes at a given intravascular pressure. At the network level, NO deficiencies lead to an increase in pressure drop across the vessels studied, a downward shift in the pressure‐flow curve, and a decrease in the effective range of the autoregulatory response. Conclusions: Our model predicts the steady state and transient behavior of resistance vessels to perturbations in blood pressure, including effects of NO bioavailability on vascular regulation. [ABSTRACT FROM AUTHOR]

Nitric oxide (NO) generated from nitrite through nitrite reductase activity in red blood cells has been proposed to play a major role in hypoxic vasodilation. However, we have previously predicted from mathematical modeling that much more NO can be derived from tissue nitrite reductase activity than from red blood cell nitrite reductase activity. Evidence in the literature suggests that tissue nitrite reductase activity is associated with xanthine oxidoreductase (XOR) and/or aldehyde oxidoreductase (AOR). We investigated the role of XOR and AOR in nitrite-mediated vasodilation from computer simulations and from in vivo exteriorized rat mesentery experiments. Vasodilation responses to nitrite in the superfusion medium bathing the mesentery equilibrated with 5% O2 (normoxia) or zero O2 (hypoxia) at either normal or acidic pH were quantified. Experiments were also conducted following intraperitoneal (IP) injection of nitrite before and after inhibiting XOR with allopurinol or inhibiting AOR with raloxifene. Computer simulations for NO and O2 transport using reaction parameters reported in the literature were also conducted to predict nitrite-dependent NO production from XOR and AOR activity as a function of nitrite concentration, PO2 and pH. Experimentally, the largest arteriolar responses were found with nitrite >10mM in the superfusate, but no statistically significant differences were found with hypoxic and acidic conditions in the superfusate. Nitrite-mediated vasodilation with IP nitrite injections was reduced or abolished after inhibiting XOR with allopurinol (p < 0.001). Responses to IP nitrite before and after inhibiting AOR with raloxifene were not as consistent. Our mathematical model predicts that under certain conditions, XOR and AOR nitrite reductase activity in tissue can significantly elevate smooth muscle cell NO and can serve as a compensatory pathway when endothelial NO production is limited by hypoxic conditions. Our theoretical and experimental results provide further evidence for a role of tissue nitrite reductases to contribute additional NO to compensate for reduced NO production by endothelial nitric oxide synthase during hypoxia. Our mathematical model demonstrates that under extreme hypoxic conditions with acidic pH, endogenous nitrite levels alone can be sufficient for a functionally significant increase in NO bioavailability. However, these conditions are difficult to achieve experimentally. [ABSTRACT FROM AUTHOR]

In 1999 we reported an important demonstration of a working brain-machine interface (BMI), in which recordings from multiple, single neurons in sensorimotor cortical areas of rats were used to directly control a robotic arm to retrieve a water reward. Subsequent studies in monkeys, using a similar approach, demonstrated that primates can use a BMI device to control a cursor on a computer screen and a robotic arm. Recent studies in humans with spinal cord injuries have shown that recordings from multiple, single neurons can be used by the patient to control the cursor on a computer screen. The promise is that one day it will be possible to use these control signals from neurons to reactivate the patient's own limbs. However, the ability to record from large populations of single neurons for long periods of time has been hampered because either the electrode itself fails or the immunological response in the tissue surrounding the microelectrode produces a glial scar, preventing single-neuron recording. While we have largely solved the problem of mechanical or electrical failure of the electrode itself, much less is known about the long term immunological response to implantation of a microelectrode, its effect on neuronal recordings and, of greatest importance, how it can be reduced to allow long term single neuron recording. This article reviews materials approaches to resolving the glial scar to improve the longevity of recordings. The work to date suggests that approaches utilizing bioactive interventions that attempt to alter the glial response and attract neurons to the recording site are likely to be the most successful. Importantly, measures of the glial scar alone are not sufficient to assess the effect of interventions. It is imperative that recordings of single neurons accompany any study of glial activation because, at this time, we do not know the precise relationship between glial activation and loss of neuronal recordings. Moreover, new approaches to immobilize bioactive molecules on microelectrode surfaces while maintaining their functionality may open new avenues for very long term single neuron recording. Finally, it is important to have quantitative measures of glial upregulation and neuronal activity in order to assess the relationship between the two. These types of studies will help rationalize the study of interventions to improve the longevity of recordings from microelectrodes. [ABSTRACT FROM AUTHOR]

The purpose of this investigation was to study the effect of the presence of red blood cells (RBCs) in the plasma layer near the arteriole wall on nitric oxide (NO) and oxygen (O2) transport. To this end, we extended a coupled NO and O2 diffusion-reaction model in the arteriole, developed by our group, to include the effect of the presence of RBCs in the plasma layer and the effect of convection. Two blood flow velocity profiles (plug and parabolic) were tested. The average hematocrit in the bloodstream was assumed to be constant in the central core and decreasing to zero in the boundary layer next to the endothelial surface layer. The effect of the presence or absence of RBCs near the endothelium was studied while varying the endothelial surface layer and boundary layer thickness. With RBCs present in the boundary layer, the model predicts that 1) NO decreases significantly in the endothelium and vascular wall; 2) there is a very small increase in endothelial and vascular wall Po2; 3) scavenging of NO by hemoglobin decreases with increasing thickness of the boundary layer; 4) the shape of the velocity profile influences both NO and Po2 gradients in the bloodstream; and 5) the presence of RBCs in the boundary layer near the endothelium has a much larger effect on NO than on O2 transport. [ABSTRACT FROM AUTHOR]

Presents a study where the stresses acting on the luminal surface of endothelial cells due to shear flow were determined on a subcellular scale. Flow perturbations; Consideration of cell-scale variations in shear stress; Normalized peak shear stress and shear stress gradient in aligned and nonaligned endothelial cells.

Discusses spatial relationships that influence signaling responses initiated by hemodynamic shear stresses in endothelial cells. Endothelial bioresponses to hemodynamic forces; Flow-sensitive signaling pathways for nitric oxide and other acute vasoregulators; Endothelial cystoskeleton in flow signaling.

Determines the molecular mechanisms of cell death and neuroprotection by poloxamer 188 after mechanical trauma. Mechanical injury induced both necrosis and apoptosis in neuronal cells mimmicking in vivo findings; Acute repair of imjured plasma membrane prevents both necrosis and apoptosis in injured cells; Conclusion and significance of the study.