In vitro assessment of a combined radiofrequency ablation and cryo-anchoring catheter for treatment of mitral valve prolapse

Percutaneous approaches to mitral valve repair are an attractive alternative to surgical repair or replacement. Radiofrequency ablation has the potential to approximate surgical leaflet resection by using resistive heating to reduce leaflet size, and cryogenic temperatures on a percutaneous catheter can potentially be used to reversibly adhere to moving mitral valve leaflets for reliable application of radiofrequency energy. We tested a combined cryo-anchoring and radiofrequency ablation catheter using excised porcine mitral valves placed in a left heart flow loop capable of reproducing physiologic pressure and flow waveforms. Transmitral flow and pressure were monitored during the cryo-anchoring procedure and compared to baseline flow conditions, and the extent of radiofrequency energy delivery to the mitral valve was assessed post-treatment. Long term durability of radiofrequency ablation treatment was assessed using statically treated leaflets placed in a stretch bioreactor for four weeks. Transmitral flow and pressure waveforms were largely unaltered during cryo-anchoring. Parameter fitting to mechanical data from leaflets treated with radiofrequency ablation and cryo-anchoring revealed significant mechanical differences from untreated leaflets, demonstrating successful ablation of mitral valves in a hemodynamic environment. Picrosirius red staining showed clear differences in morphology and collagen birefringence between treated and untreated leaflets. The durability study indicated that statically treated leaflets did not significantly change size or mechanics over four weeks. A cryo-anchoring and radiofrequency ablation catheter can adhere to and ablate mitral valve leaflets in a physiologic hemodynamic environment, providing a possible percutaneous alternative to surgical leaflet resection of mitral valve tissue.     

The TRPM2 channel: A thermo-sensitive metabolic sensor

Living organisms continually experience changes in ambient temperature. To detect such temperature changes for adaptive behavioral responses, we evolved the ability to sense temperature. Thermosensitive transient receptor potential (TRP) channels, so-called thermo-TRPs, are involved in many physiologic functions in diverse organisms and constitute important temperature sensors. One of the important roles of thermo-TRPs is detecting ambient temperature in sensory neurons. Importantly, the functional expression of thermo-TRPs is observed not only in sensory neurons but also in tissues and cells that are not exposed to drastic temperature changes, indicating that thermo-TRPs are involved in many physiologic functions within the body's normal temperature range. Among such thermo-TRPs, this review focuses on one thermo-sensitive metabolic sensor in particular, TRPM2, and summarizes recent progress to clarify the regulatory mechanisms and physiologic functions of TRPM2 at body temperature under various metabolic states.     

Dietary unsaturated fatty acids: interactions and possible needs in relation to eicosanoid synthesis

In addition to providing energy and essential fatty acids, dietary fatty acids can affect numerous biochemical and physiologic reactions related to secretory, cardiovascular, and immune functions. The major dietary unsaturated fatty acid, linoleic acid, affects tissue arachidonic acid and can influence eicosanoid-mediated reactions. Chronic, excess, or imbalanced eicosanoid synthesis may be conductive to excessive inflammation, thrombotic tendencies, atherosclerosis, and immune suppression. Dietary n-3 polyunsaturated fatty acids (PUFAs) may ameliorate eicosanoid-related phenomena by reducing tissue arachidonic acid and by inhibiting eicosanoid synthesis. This review summarizes information concerning the metabolism of unsaturated fatty acids, with emphasis on tissue arachidonic acid levels and eicosanoids, and discusses the need for data concerning the appropriate intake of dietary n-6 and n-3 PUFAs to modulate arachidonic acid and eicosanoid synthesis and to minimize possible adverse reactions.     

Histochemical localization of opiate receptors and opioid peptides.

It is possible to localize opiate receptors by histochemical methods. They appear in high densities in anatomical areas associated with physiologic functions altered by opiates. They appear to mediate inhibitory responses; some of them, in certain regions could be involved in axo-axonic synapses. The immunohistochemical studies as well as the electrophysiologic results are compatible with the view that the enkephalins are the endogenous substrates for the opiate receptors.     

Mechanisms and Physiologic Significance of Microwave Action on the Auditory System

Studies conducted by the authors and their coworkers on the mechanisms and physiologic significance of radiofrequency hearing effects are reviewed. Results of these studies demonstrate that 1) thermoelastic expansion of fluids and structures within the inner ear is the main mechanism by which auditory stimuli are produced by microwave pulses; 2) the frequency spectra of these stimuli are indistinguishable from the spectra of rectangular pulses with the same durations as the microwave pulses; 3) exposure to continuous-wave (CW) microwave radiation evokes an increase in the metsbolic activities of nuclei in the ascending auditory pathway and also decreases the latency and increases the magnitude of brainstem-evoked responses produced by acoustic clicks; and 4) the mechanism of the effects of CW microwave radiation on the auditory system is intracochlear heating. The significance of these findings is discussed in terras of potential applications of microwave stimuli in basic research on the auditory system and in terms of interpreting the results of past studies that demonstrate behavioral sensitivity to CW microwave fields.     

Mutations of immunoglobulin transmembrane and cytoplasmic domains: effects on intracellular signaling and antigen presentation

The membrane-bound form of immunoglobulin serves as an antigen-specific receptor for B cells mediating signal transduction and antigen presentation. We have developed an assay that reconstitutes both these physiologic responses with respect to the antigen phosphorylcholine. By introducing specific mutations in the human Ig mu chain gene, we have shown that certain transmembrane residues and the short cytoplasmic domain are crucial for these two activities. Moreover, elimination of a single transmembrane hydroxyl group severely inhibits antigen presentation without affecting signal transduction, suggesting that these two functions are mediated by different protein interactions.     

An evaluation of respiration chain-associated functions during initiation of germination of Bacillus megaterium spores

In Bacillus megaterium QM B1551, spore germination could be initiated by glucose in the absence of detectable oxygen consumption, ATP synthesis or a pH decrease in the external media, suggesting that none of those reactions were mandatory. In addition, initiation of germination was insensitive to a variety of inhibitors of energy production or protonmotive force uncouplers. Therefore the respiratory chain-associated functions are not prerequisites for initiation of germination but these functions may be necessary to drive energy-dependent transport systems and other biosynthetic reactions during outgrowth.     

Aggressive behavior, its adaptive function and mechanisms of development of psychosomatic disorders and diseases of adaptation

A correlation between physiologic and behavioral responses to emotional stress and agonistic conflict (triad model), as well as ideas of autonomic-humoral support of subsequent activity suggest that motor activity and situational aggressive behavior are essential final stages of stress reaction and, therefore, mechanisms of adaptation. Failure in final the stage of adaptive response causes mobilization changes to be directed against the host organism itself. This phenomenon forms the basis for psychosomatic disorders. Aggression seems to be an adaptive response not only from ethologic, but from physiologic point of view as well. It has some elements of homeostatic control (together with non-homeostatic functions). Homeostatic role of aggression may be in "elimination" of mobilization metabolic changes caused by stress reaction and physical activity by means of expressive emotional response. Aggression as a non-homeostatic factor has an ethologic function.     

Cognitive and physiologic responses to EMG biofeedback and three types of pseudofeedback during a muscular relaxation task

Four groups of normal human subjects were tested for their ability to reduce frontal muscle tension levels during presentation of veridical auditory biofeedback or auditory pseudofeedback. A double-blind methodology was used. Three groups of subjects assigned to the pseudofeedback conditions received a feedback signal that was not contingent on EMG activity but that followed one of three different patterns. One group received a truly random signal, the second received a signal that gradually increased in frequency (apparent failure), and the third received a signal that gradually decreased in frequency (apparent success). Dependent measures included both physiologic (frontal and neck EMG) and subjective reactions to the relaxation task. The different patterns of pseudofeedback did produce reliably different subjective responses, suggesting that the manipulations succeeded in producing unequal nonspecific effects that were unrelated to the feedback contingency specifically. However, these differential subjective effects were not strongly reflected in the physiologic responses since the differences in EMG levels among the four groups did not differ significantly at any stage of training. An analysis of the integrity of the double-blind procedure showed that although experimenters were effectively kept blind to group assignment, subjects' responding suggested a response bias as well as the possibility that the double-blind was breached. The utility of the double-blind methodology in biofeedback experiments is discussed and suggestions for future research are offered.     

Physiologic control of the functional status of Foxp3+ regulatory T cells

Foxp3-lineage CD4 regulatory T cells (Tregs) were named for their ability to maintain self tolerance and suppress T cell immunity. However, resting Tregs from noninflamed tissues exhibit little suppressor activity, and must be stimulated to acquire such function. Conversely, under certain inflammatory conditions, Tregs may undergo rapid reprogramming to acquire helper/effector functions. In this Brief Review, we describe recent progress in elucidating physiologic processes that control the functional status of Foxp3-lineage Tregs. Emerging evidence suggests the surprising possibility that reprogrammed Tregs can be an indispensable source of helper activity in some physiologic settings, such as priming CD8(+) T cell responses. This suggests a novel paradigm in which Foxp3(+) Tregs intrinsically possess bifunctional potential, acting as a preformed pool of first-responder cells at sites of local inflammation that can either provide classical regulatory/suppressor activity, or rapidly reprogram to supply helper/effector activity, contingent on signals that manifest in local physiologic settings.     

An evaluation of respiration chain-associated functions during initiation of germination of Bacillus megaterium spores.

In Bacillus megaterium QM B1551, spore germination could be initiated by glucose in the absence of detectable oxygen consumption, ATP synthesis or a pH decrease in the external media, suggesting that none of those reactions were mandatory. In addition, initiation of germination was insensitive to a variety of inhibitors of energy production or protonmotive force uncouplers. Therefore the respiratory chain-associated functions are not prerequisites for initiation of germination but these functions may be necessary to drive energy-dependent transport systems and other biosynthetic reactions during outgrowth.     

Carbohydrates: a limit on bacterial diversity within the colon

The human large intestine is recognised as a physiologically important organ responsible for the conservation of water and salts. Through its resident bacteria, it is also capable of complex, enzyme catalysed, hydrolytic-digestive functions that have a high biological impact on the host. These microorganisms metabolise dietary components, principally complex carbohydrates that are not hydrolysed or absorbed in the upper gastrointestinal tract, and in this way, sequester energy for the host, through fermentation. This process involves a series of anaerobic, energy-yielding, catabolic reactions which complete digestive processes in the gut, resulting in end products that in turn influence the distribution of microbial species present as well as having some systemic effects. Some of the bacteria are thought to possess important health-promoting activities, especially with respect to their influence on mucosal and systemic immune responses to disease. These bioactivities can be modulated by substrates that support and influence microbial development, growth and survival. For these reasons, it is necessary to review dietary factors that may delimit bacterial diversity, to be able to predict responses and sensitivities to various environmental pressures and manipulations that occur in this area of human microbiology.     

Degradation of plasmodial antigens by human neutrophil elastase

Human neutrophil elastase (HNE) has been well-studied with respect to its role in pathologic states, but less is known about the physiologic functions of this important granulocyte enzyme. In the present study, we show that HNE can degrade the major circumsporozoite protein of the infective (sporozoite) stage of Plasmodium vivax malaria, and that this enzyme can also interfere with the cytoadherence of human E infected with Plasmodium falciparum (strain K+ FMG-FCR3) (IE). Cytoadherence reactions are not only blocked by treatment of IE with as little as 10 fg HNE/IE, but already adherent IE are also removed by the enzyme. Normal E surface Ag are not extensively destroyed by these doses of HNE. This suggests that the effect of HNE on cytoadherence is selective and probably due to degradation of the malarial Ag exported to the IE surface and responsible for the formation of "recognition knobs" upon which the cytoadherence reaction depends. This conclusion, in turn, was supported by the results of Western blot analysis showing that HNE degrades a high m.w. Ag found exclusively in membrane extracts of IE. Our results suggest that one physiologic role of HNE may be degradation of parasitic antigens during host defense against malaria.     

Glucocorticoid-induced TNF receptor, a costimulatory receptor on naive and activated T cells, uses TNF receptor-associated factor 2 in a novel fashion as an inhibitor of NF-kappa B activation

Glucocorticoid-induced TNFR (GITR) has been implicated as an essential regulator of immune responses to self tissues and pathogens. We have recently shown that GITR-induced cellular events promote survival of naive T cells, but are insufficient to protect against activation-induced cell death. However, the molecular mechanisms of GITR-induced signal transduction that influence physiologic and pathologic immune responses are not well understood. TNFR-associated factors (TRAFs) are pivotal adapter proteins involved in signal transduction pathways of TNFR-related proteins. Yeast two-hybrid assays and studies in HEK293 cells and primary lymphocytes indicated interactions between TRAF2 and GITR mediated by acidic residues in the cytoplasmic domain of the receptor. GITR-induced activation of NF-kappaB is blocked by A20, an NF-kappaB-inducible protein that interacts with TRAFs and functions in a negative feedback mechanism downstream of other TNFRs. Interestingly, in contrast with its effects on signaling triggered by other TNFRs, our functional studies revealed that TRAF2 plays a novel inhibitory role in GITR-triggered NF-kappaB activation.     

A transition state theory approach to the kinetics of conductance changes in excitable membranes

Summary The kinetics of ionic current mechanisms in excitable membranes are analyzed. It is assumed that there are voltage-dependent reactions occurring in the membrane which are independent of the flow of ionic current. The experimental evidence for this assumption is reviewed in the light of more recent results on the kinetics of conductance changes in cardiac membranes. Rate equations are then obtained using transition state theory and assuming that each reaction is rate limited by only one energy barrier. These equations give simple exponential functions for the voltage dependence of the rates. More complex functions may be obtained by assuming that more than one energy barrier is rate limiting. The single-barrier equations are used to estimate the energies of formation of the transition state. In most cases, the entropy of formation is positive but there is no systematic order in the estimated enthalpies. These results are contrasted with those for the ion permeation process itself which normally has a negative entropy of activation. This contrast reinforces the assumption that the reactions controlling membrane permeability are distinct from the ion permeation process itself. The significance of the positive entropy of formation of the transition state in the permeability reactions is discussed, and it is suggested that the membrane structures underlying these reactions may change their degree of hydration during the formation of the transition state.     

Microbial energetics

An understanding of the mechanisms by which bacteria derive their energy is clearly important for the prediction of growth yields. Bacteria can synthesize ATP by a variety of routes, by fermentation, by oxidative phosphorylation, and possibly by the excretion of metabolic end products. The bacterium Escherichia coli has been studied extensively and a great deal is now known about the different membrane-bound multi-enzyme complexes that are responsible for oxidative phosphorylation. The efficiency of oxidative phosphorylation can vary not only between different bacteria that have adapted to particular ecological niches but also in an individual bacterium grown under different conditions or modified genetically by mutation with respect to its parent. Clearly, the concept that bacteria always grow with maximum thermodynamic efficiency is erroneous and it is important, therefore, to be able to assess the efficiency of energy conversion as well as the biochemical and genetical factors that regulate the physiological expression of energy-yielding reactions if they are to be manipulated by the investigator.     

Plasma catecholamines and their physiologic thresholds during the first ten days of life in sheep

We studied serial plasma catecholamine levels in healthy newborn sheep over the first ten days of life. The results show that plasma norepinephrine values in newborn sheep are 3-4 fold higher, and plasma epinephrine values are two-fold higher than values in term fetal sheep. These elevations are sustained over the first 10 days of life. Cardiovascular (heart rate and blood pressure) and metabolic parameters (glucose and free fatty acids) are also significantly elevated above fetal levels. We performed graded catecholamine infusions in newborn animals and adult ewes to determine the minimum plasma catecholamine concentrations necessary for discernible physiologic effects. In response to step-wise increases in epinephrine or norepinephrine infusion rates, there were immediate increases in blood pressure and other physiologic responses. This pattern was seen in both newborn and adult animals, and differed from previous observations in fetal sheep where log-linear, dose response curves characteristic of a threshold response were seen. These results suggest that during the first two weeks of life plasma catecholamine levels are elevated above the threshold value for physiologic responses. These sustained elevations in circulating catecholamines are important in the maintenance of physiologic homeostasis.     

Airway epithelium and apoptosis

Recent advances revealed that airway epithelium possesses versatile functions and plays a vital role in the mucosal defense and inflammatory responses. A maintenance of airway epithelium integrity is thus important and appears to be tightly regulated by a balanced cell proliferation and apoptosis. However, homeostasis of airway epithelium is likely affected by multiple environmental pathogens, irritants (reactive oxygen species, allergens, etc.), and toxins that may lead to various lung diseases. This review briefly summarizes airway epithelium apoptosis/proliferation in physiologic and pathological conditions along with various factors influencing airway epithelium homeostasis.     

Control of whole heart geometry by intramyocardial mechano-feedback: a model study

Geometry of the heart adapts to mechanical load, imposed by pressures and volumes of the cavities. We regarded preservation of cardiac geometry as a homeostatic control system. The control loop was simulated by a chain of models, starting with geometry of the cardiac walls, sequentially simulating circulation hemodynamics, myofiber stress and strain in the walls, transfer of mechano-sensed signals to structural changes of the myocardium, and finalized by calculation of resulting changes in cardiac wall geometry. Instead of modeling detailed mechano-transductive pathways and their interconnections, we used principles of control theory to find optimal transfer functions, representing the overall biological responses to mechanical signals. As biological responses we regarded tissue mass, extent of contractile myocyte structure and extent of the extra-cellular matrix. Mechano-structural stimulus-response characteristics were considered to be the same for atrial and ventricular tissue. Simulation of adaptation to self-generated hemodynamic load rendered physiologic geometry of all cardiac cavities automatically. Adaptation of geometry to chronic hypertension and volume load appeared also physiologic. Different combinations of mechano-sensors satisfied the condition that control of geometry is stable. Thus, we expect that for various species, evolution may have selected different solutions for mechano-adaptation.     

Artificial gravity in space flight

Clearly, physiologic adaptation to terrestrial life for all animals is assured only by frequent encounters with gravity. Indeed, upon exposure to weightlessness in space flight, losses of physiologic functions quickly begin. Some physiologic parameters change more rapidly than others, but the deconditioning process starts rapidly. The rates of functional losses for all affected parameters are interesting in that they appear to approach a limit; i.e., losses of these functions may not continue until indefinitely. The regulation of this functional asymptotic response to space is not known, but probably based on functional requirements of the body to life itself and perhaps genetic expression. The latter controlling mechanism (DNA) functions only on aquatic (weightless) animals on Earth--land animals must stimulate these physiologic functions as they relate to gravity on a regular frequent basis. This loss of regulation upon entering the weightless environment is fascinating since land-based animals including the humans have evolved from millions (perhaps billions) of years of terrestrially adapted ancestors. One would expect some DNA involvement in the regulation of its physiology, but it appears to be absent. Therefore, if the functional debilitation of space is to be denied, we must begin to understand the adaptation process of the sole basis for the control of our physiologic processes on land; i.e., how gravity regulates our biologic functions. To learn about this regulatory mechanism, some inquiry into how aquatic animals first adapted to living on land might be helpful.