Acid-Sensing Ion Channels and Mechanosensation

Acid-sensing ion channels (ASICs) are mainly proton-gated cation channels that are activated by pH drops and nonproton ligands. They are part of the degenerin/epithelial sodium channel superfamily due to their sodium permeability. Predominantly expressed in the central nervous system, ASICs are involved in synaptic plasticity, learning/memory, and fear conditioning. These channels have also been implicated in multiple disease conditions, including ischemic brain injury, multiple sclerosis, Alzheimer’s disease, and drug addiction. Recent research has illustrated the involvement of ASICs in mechanosensation. Mechanosensation is a form of signal transduction in which mechanical forces are converted into neuronal signals. Specific mechanosensitive functions have been elucidated in functional ASIC1a, ASIC1b, ASIC2a, and ASIC3. The implications of mechanosensation in ASICs indicate their subsequent involvement in functions such as maintaining blood pressure, modulating the gastrointestinal function, and bladder micturition, and contributing to nociception. The underlying mechanism of ASIC mechanosensation is the tether-gate model, which uses a gating-spring mechanism to activate ASIC responses. Further understanding of the mechanism of ASICs will help in treatments for ASIC-related pathologies. Along with the well-known chemosensitive functions of ASICs, emerging evidence has revealed that mechanosensitive functions of ASICs are important for maintaining homeostasis and contribute to various disease conditions.

The optical detection of retinal ganglion cell damage

We provide an overview of developments in the use optical coherence tomography (OCT) imaging for the detection of retinal ganglion cell (RGC) damage in vivo that avoid use of any exogenous ligands to label cells. The method employs high-resolution OCT using broad spectral light sources to deliver axial resolution of under 5 μm. The resolution approximates that of cellular organelles, which undergo degenerative changes that progress to apoptosis as a result of axon damage. These degenerative changes are manifest as the loss of RGC dendrites and fragmentation of the subcellular network of organelles, in particular, the mitochondria that support dendritic structure. These changes can alter the light-scattering behavior of degenerating neurons. Using OCT imaging techniques to identify these signals in cultured neurons, we have demonstrated changes in cultured cells and in retinal explants. Pilot studies in human glaucoma suggest that similar changes are detectable in the clinical setting. High-resolution OCT can be used to detect optical scatter signals that derive from the RGC/inner plexiform layer and are associated with neuronal damage. These findings suggest that OCT instruments can be used to derive quantitative measurements of RGC damage. Critically, these signals can be detected at an early stage of RGC degeneration when cells could be protected or remodeled to support visual recovery.

Custom designed acoustic pulses

We have used a tunable, infrared, free-electron laser with a Pockels cell controlled pulse duration to generate photoacoustic pulses with separate variable rise times (from 15 to 100 ns), durations (100-400 ns), and amplitudes (0.005-0.1 MPa). The tunability of the free-electron laser across water absorption bands allows the rise time of the thermal-elastically generated acoustical pulsed to be varied, while a Pockels cell controls the duration and cross polarizers control the pressure amplitude. The mechanical effects of pressure transients on biological tissue can have dramatic consequences. In addition to cell necrosis, carefully controlled pressure transients can also be used for therapeutic applications, such as drug delivery and gene therapy. This technique permits systemic probing of how biological tissue is affected by stress transients. © 1999 Society of Photo-Optical Instrumentation Engineers.

College women's perceptions regarding resistance to sexual assault

College women's perceptions about resistance to sexual assault were examined. Twenty-one percent of the 334 women surveyed stated that they had been sexually assaulted. The vast majority of participants had changed their lifestyles to prevent a sexual assault. Less than 1 woman in 5 of those surveyed had taken a self-defense class. Participants believed that resisting sexual assault by a stranger with a weapon was more likely than resisting an unarmed attacker to increase their chances of being physically harmed, raped, or murdered. Twenty-two percent of the participants said they were "very likely" to resist sexual assault by a stranger with a weapon; 52% would resist a stranger without a weapon. The findings indicate the need for an increase in the number of women taking self-defense classes and a revision in women's perceptions about resisting sexual assault.

Tissue ablation by a free-electron laser tuned to the amide II band

Efforts to ablate soft tissue with conventional lasers have been limited by collateral damage and by concern over potential photochemical effects. Motivated by the thermal-confinement model, past infrared investigations targeted the OH-stretch mode of water with fast pulses from lasers emitting near 3,000 nm (refs 1, 7-9). What does a free-electron laser offer for the investigation of tissue ablation? Operating at non-photochemical single-photon energies, these infrared sources can produce trains of picosecond pulses tunable to the vibrational modes of proteins, lipids and/or water. We report here that targeting free-electron laser radiation to the amide II band of proteins leads to tissue ablation characterized by minimal collateral damage while maintaining a substantial ablation rate. To account for these observations we propose a novel ablation mechanism based on compromising tissue through resonant denaturation of structural proteins.

Noninvasive optical diagnosis of bacteria causing otitis media

Currently, the identification of the bacteria responsible for acute otitis media requires a painful invasive procedure: tympanocentesis. To develop a rapid and noninvasive technique for bacterial diagnosis, the fluorescence profiles of four common pathogens and the optical characteristics of the tympanic membrane have been investigated. Each bacterium produces a unique in vitro fluorescence profile when measured in a saline suspension. Also, spectrally resolved transmission measurements from the chinchilla tympanic membrane demonstrate an optical window that will transmit sufficient light for in vivo measurement of the fluorescence profiles. Thus, we have established the precept for a fluorescence-based bacterial diagnosis technique to be used in otitis media. This paper presents the theory, optical data, and a discussion of the device engineering involved in the technique.

Bacteria identification of otitis media with fluorescence spectroscopy

We have investigated the fluorescence profiles of four common pathogens: S. pneumoniae, S. aureus, M. catarrhalis, and H. influenzae. The steady-state auto fluorescence spectra of bacteria are measured as a function of the incident light from 200 to 700 nm. The spectra for each bacterium are combined into a fluorescence profile or fluorescence finger print. Each bacterium produces a unique in vitro fluorescence profile when measured in a saline suspension. The profiles are reproducible. Suspensions of a bacterial strain, where the identification is not known, can be correctly matched to a small library of previously measured fluorescence profiles using a linear least-squares fitting algorithm. In addition, we have measured the fluorescence and absorption spectrum of the tympanic membrane removed from a chinchilla. The optical properties of the tympanic membrane and the least-squares identification process form precept for a non-invasive, fluorescence based bacterial diagnosis technique to be used in otitis media.

Role of immersion refractometry for investigating laser-induced effects in cells

The broad background of scattered light observed in spectra of cell suspensions is reduced by factors of up to 20 by immersion refractometry allowing for improved spectroscopic determination of the absorption properties of cells in the 325-820 nm range. Refractive-index matched spectra of E. coli C1a exhibit a set of resonant features near 422, 561, and 582 nm. Exposure wavelengths are chosen based on this spectrum and cell viability is investigated in E. coli suspensions exposed to 350, 400, 422, 440, and 700 nm radiation delivered in nanosecond pulses with total doses from 500 millijoules to 60 Joules. We observe a loss in cell viability for doses greater than 1 Joule at 422 nm and for all doses at other wavelengths; exposures of less than 1 Joule at 422 nm enhance growth. Excluding exposures at wavelengths within the resonant feature, longer wavelengths are less effective at reducing the viability of E. coli C1a. This indicates the occurrence of at least two absorption processes.

Treatment of severe imipramine poisoning complicated by a negative history of drug ingestion

The wide use of imipramine (Tofranil) for the treatment of nocturnal enuresis continues in spite of the unique dangers associated with this drug. Young children are particularly susceptible to the potentially lethal central nervous system and cardiovascular toxicities, yet the toxic potential of imipramine remains unrecognized by both parents and too many physicians. Management of severe imipramine intoxication can be difficult. This report describes a 12-month-old patient with severe imipramine intoxication whose treatment was complicated by a negative history at presentation.

A model of atrial ectopic tachycardia in the rat

A model of atrial ectopic tachycardia (AET) in the adult rat is described. Pentobarbital-anesthetized adult male rats given digoxin 30 mg/kg s.c. develop AET 50 min after administration. Heart rate and rhythm were determined by electrocardiography using limb leads, I, II and III. This model of AET is simple, sustained and economical. As a supplement to models of ventricular arrhythmias, this model might broaden the pre-clinical evaluation of antiarrhythmic agents.

Reevaluation of digoxin-encainide interactions using an animal model

The effects of intravenous encainide on digoxin-induced atrial ectopic tachycardia (AET) were investigated in the rat using 3-channel simultaneous limb-lead electrocardiography. Pentobarbital-anesthetized (35 mg/kg, intraperitoneal) adult male rats were given digoxin subcutaneously, 30 mg/kg. After onset of AET, rats received either saline (0.5 ml/kg) or encainide; 0.25, 0.5, 1.0, or 2.0 mg/kg intravenously in repeated doses at 15-min intervals. At all doses, encainide converted digoxin-induced AET to ventricular arrhythmias, prolonged recovery time, and increased mortality in comparison to saline-treated animals. An additional group of anesthetized rats was not given digoxin. These animals received encainide (2.0 mg/kg, intravenously) in repeated doses at 15-min interval and developed dose-related increase in the P-R interval only. Blood samples were obtained by cardiac puncture from 12 additional anesthetized, digoxin-treated rats 5 min after the fourth intravenous dose of saline (0.5 ml/kg, n = 6) or encainide (1.0 mg/kg, n = 6). Serum was prepared and analyzed by affinity column-mediated immunoassay. Digoxin levels were the same in both groups. These results suggest that encainide may exacerbate digoxin-induced arrhythmias (proarrhythmic effect) in this species. In view of our findings of digoxin-encainide interactions in the rat, we recommend caution if these drugs are coadministered in humans.