Enhanced chemiluminescent detection scheme for trace vapor sensing in pneumatically-tuned hollow core photonic bandgap fibers.

We demonstrate an in-fiber gas phase chemical detection architecture in which a chemiluminescent (CL) reaction is spatially and spectrally matched to the core modes of hollow photonic bandgap (PBG) fibers in order to enhance detection efficiency. A peroxide-sensitive CL material is annularly shaped and centered within the fiber's hollow core, thereby increasing the overlap between the emission intensity and the intensity distribution of the low-loss fiber modes. This configuration improves the sensitivity by 0.9 dB/cm compared to coating the material directly on the inner fiber surface, where coupling to both higher loss core modes and cladding modes is enhanced. By integrating the former configuration with a custom-built optofluidic system designed for concomitant controlled vapor delivery and emission measurement, we achieve a limit-of-detection of 100 parts per billion (ppb) for hydrogen peroxide vapor. The PBG fibers are produced by a new fabrication method whereby external gas pressure is used as a control knob to actively tune the transmission bandgaps through the entire visible range during the thermal drawing process.

Efficient LED light distribution cavities using low loss, angle-selective interference transflectors.

Recent advances in solid state light source efficiency and luminance present the technical challenge of distributing light from very small point sources to large areas, with area distribution ratios having orders of magnitude greater than previously addressed. Broad adoption of LEDs in lighting and liquid crystal displays is in part contingent on addressing this fundamental light distribution issue. Here we present new materials based on giant birefringent nanotechnology which address these deficiencies allowing us to guide light in air via a novel light distribution system. Resulting from controlled in-plane and out-of-plane x,y,z refractive indices of adjacent layers, these multilayer interference films possess both angle selective and polarization selective reflectance. The angle selectivity can be tuned in both azimuth and polar angle, relieving a key constraint of prior materials. Our work has been done on a physically large scale enabling demonstration of large light management systems of industrial and practical relevance.

Rabbit, a relevant model for the study of cardiac beta 3-adrenoceptors.

The beta(3)-adrenoceptors (beta(3)-ARs) have been identified and characterized in the human heart. Specific beta(3)-AR stimulation, unlike beta(1)-AR or beta(2)-AR stimulation, decreases cardiac contractility, partly via the G(i)-NO pathway. However, the precise role of cardiac beta(3)-ARs is not yet completely understood. Indeed, under normal conditions, the beta(3)-AR response is present only to a very low degree in rats and mice. Therefore, we evaluated whether beta(3)-ARs were present and functional in rabbit ventricular cardiomyocytes, and whether the rabbit could serve as a relevant model for the study of cardiac beta(3)-ARs. We used RT-PCR and Western blot to measure the beta(3)-AR transcripts and protein levels in rabbit ventricular cardiomyocytes. We also analysed the effect of beta(3)-AR stimulation using isoproterenol in combination with nadolol or SR 58611A on cardiomyocyte shortening, Ca(2+) transient, L-type Ca(2+) current (I(Ca,L)), delayed rectifier potassium current (I(Ks)) and action potential duration (APD). For the first time, we show that beta(3)-ARs are expressed in rabbit ventricular cardiomyocytes. The mRNA and protein sequences present a high homology to those of rat and human beta(3)-ARs. Furthermore, beta(3)-AR stimulation decreases cardiomyocyte shortening, Ca(2+) transient and I(Ca,L) amplitudes, via a G(i)-NO pathway. Importantly, beta(3)-AR stimulation enhances I(Ks) amplitude and shortens the APD. Taken together, our results indicate that the rabbit provides a relevant model, easily used in laboratories, to study the roles of cardiac beta(3)-ARs in physiological conditions.

PI3Kgamma is required for PDE4, not PDE3, activity in subcellular microdomains containing the sarcoplasmic reticular calcium ATPase in cardiomyocytes.

We recently showed that phosphoinositide-3-kinase-gamma-deficient (PI3Kgamma(-/-)) mice have enhanced cardiac contractility attributable to cAMP-dependent increases in sarcoplasmic reticulum (SR) Ca(2+) content and release but not L-type Ca(2+) current (I(Ca,L)), demonstrating PI3Kgamma locally regulates cAMP levels in cardiomyocytes. Because phosphodiesterases (PDEs) can contribute to cAMP compartmentation, we examined whether the PDE activity was altered by PI3Kgamma ablation. Selective inhibition of PDE3 or PDE4 in wild-type (WT) cardiomyocytes elevated Ca(2+) transients, SR Ca(2+) content, and phospholamban phosphorylation (PLN-PO(4)) by similar amounts to levels observed in untreated PI3Kgamma(-/-) myocytes. Combined PDE3 and PDE4 inhibition caused no further increases in SR function. By contrast, only PDE3 inhibition affected Ca(2+) transients, SR Ca(2+) loads, and PLN-PO(4) levels in PI3Kgamma(-/-) myocytes. On the other hand, inhibition of PDE3 or PDE4 alone did not affect I(Ca,L) in either PI3Kgamma(-/-) or WT cardiomyocytes, whereas simultaneous PDE3 and PDE4 inhibition elevated I(Ca,L) in both groups. Ryanodine receptor (RyR(2)) phosphorylation levels were not different in basal conditions between PI3Kgamma(-/-) and WT myocytes and increased in both groups with PDE inhibition. Our results establish that L-type Ca(2+) channels, RyR(2), and SR Ca(2+) pumps are regulated differently in distinct subcellular compartments by PDE3 and PDE4. In addition, the loss of PI3Kgamma selectively abolishes PDE4 activity, not PDE3, in subcellular compartments containing the SR Ca(2+)-ATPase but not RyR(2) or L-type Ca(2+) channels.

Insulin-like growth factor-1 and PTEN deletion enhance cardiac L-type Ca2+ currents via increased PI3Kalpha/PKB signaling.

Ca2+ influx through the L-type Ca2+ channel (I(Ca,L)) is a key determinant of cardiac contractility and is modulated by multiple signaling pathways. Because the regulation of I(Ca,L) by phosphoinositide-3-kinases (PI3Ks) and phosphoinositide-3-phosphatase (PTEN) is unknown, despite their involvement in the regulation of myocardial growth and contractility, I(Ca,L) was recorded in myocytes isolated from mice overexpressing a dominant-negative p110alpha mutant (DN-p110alpha) in the heart, lacking the PI3Kgamma gene (PI3Kgamma(-/-)) or with muscle-specific ablation of PTEN (PTEN(-/-)). Combinations of these genetically altered mice were also examined. Although there were no differences in the expression level of CaV1.2 proteins, basal I(Ca,L) densities were larger (P<0.01) in PTEN(-/-) myocytes compared with littermate controls, PI3Kgamma(-/-), or DN-p110alpha myocytes and showed negative shifts in voltage dependence of current activation. The I(Ca,L) differences seen in PTEN(-/-) mice were eliminated by pharmacological inhibition of either PI3Ks or protein kinase B (PKB) as well as in PTEN(-/-)/DN-p110alpha double mutant mice but not in PTEN(-/-)/PI3Kgamma(-/-) mice. On the other hand, application of insulin-like growth factor-1 (IGF-1), an activator of PKB, increased I(Ca,L) in control and PI3Kgamma(-/-), while having no effects on I(Ca,L) in DN-p110alpha or PTEN(-/-) mice. The I(Ca,L) increases induced by IGF-1 were abolished by PKB inhibition. Our results demonstrate that IGF-1 treatment or inactivation of PTEN enhances I(Ca,L) via PI3Kalpha-dependent increase in PKB activation.

Cardiac sarcoplasmic reticulum calcium release and load are enhanced by subcellular cAMP elevations in PI3Kgamma-deficient mice.

We recently showed that phosphoinositide-3-kinase-gamma-deficient (PI3Kgamma-/-) mice have increased cardiac contractility without changes in heart size compared with control mice (ie, PI3Kgamma+/+ or PI3Kgamma+/-). In this study, we show that PI3Kgamma-/- cardiomyocytes have elevated Ca2+ transient amplitudes with abbreviated decay kinetics compared with control under field-stimulation and voltage-clamp conditions. When Ca2+ transients were eliminated with high Ca2+ buffering, L-type Ca2+ currents (I(Ca,L)), K+ currents, and action potential duration (APD) were not different between the groups, whereas, in the presence of Ca2+ transients, Ca2+-dependent phase of I(Ca,L) inactivation was abbreviated and APD at 90% repolarization was prolonged in PI3Kgamma-/- mice. Excitation-contraction coupling (ECC) gain, sarcoplasmic reticulum (SR) Ca2+ load, and SR Ca(2+) release fluxes measured as Ca2+ spikes, were also increased in PI3Kgamma-/- cardiomyocytes without detectable changes in Ca2+ spikes kinetics. The cAMP inhibitor Rp-cAMP eliminated enhanced ECC and SR Ca2+ load in PI3Kgamma-/- without effects in control myocytes. On the other hand, the beta-adrenergic receptor agonist isoproterenol increased I(Ca,L) and Ca2+ transient equally by approximately 2-fold in both PI3Kgamma-/- and PI3Kgamma+/- cardiomyocytes. Our results establish that PI3Kgamma reduces cardiac contractility in a highly compartmentalized manner by inhibiting cAMP-mediated SR Ca2+ loading without directly affecting other major modulators of ECC, such as AP and I(Ca,L).

Phosphoinositide 3-kinase gamma regulates cardiac contractility by locally controlling cyclic adenosine monophosphate levels.

Class I phosphoinositide 3-kinases (PI3Ks) are enzymes with both protein and lipid kinase activities that regulate important cellular functions in many tissues. In the heart, subclass IA PI3Ks (mainly PI3Kalpha) regulate cell growth, apoptosis, cell division and cell size, whereas PI3Kgamma, the only member of subclass IB, has been shown to regulate cardiac contractility. We have shown that the loss of PI3Kgamma (PI3Kgamma(-/-) mice) enhances cardiac excitation-contraction coupling by modulating cyclic adenosine monophosphate (cAMP) levels in subcellular domains containing the sarcoplasmic reticulum. Specifically, PI3Kgamma(-/-) mice show enhanced sarcoplasmic reticulum Ca(2+) cycling in association with increased cAMP. Surprisingly, L-type Ca(2+) current, a prototypic target of cAMP-dependent protein kinase A phosphorylation, is largely unchanged in PI3Kgamma(-/-) mice. In this article, we discuss the consequences and implications of cAMP compartmentation in cardiomyocytes. We also review the different roles of PI3Kgamma in the heart, particularly as they relate to cardiac contractility, intracellular cAMP levels, and the regulation of beta-adrenergic receptor signaling in physiologic and pathologic states.

Surface-emitting fiber lasers.

All fiber lasers to date emit radiation only along the fiber axis. Here a fiber that exhibits laser emission that is radially directed from its circumferential surface is demonstrated. A unique and controlled azimuthally anisotropic optical wave front results from the interplay between a cylindrical photonic bandgap fiber resonator, anisotropic organic dye gain, and a linearly polarized axial pump. Low threshold (86nJ) lasing at nine different wavelengths is demonstrated throughout the visible and near-infrared spectra. We also report the experimental realization of unprecedented layer thicknesses of 29.5 nm maintained throughout meter-long fibers. Such a device may have interesting medical applications ranging from photodynamic therapy to in vivo molecular imaging, as well as textile fabric displays.

Mineralocorticoid receptor antagonism prevents the electrical remodeling that precedes cellular hypertrophy after myocardial infarction.

BACKGROUND: Cardiac hypertrophy underlies arrhythmias and sudden death, for which mineralocorticoid receptor (MR) activity has recently been implicated. We sought to establish the sequence of ionic events that link the initiating insult and MR to hypertrophy development. METHODS AND RESULTS: Using whole-cell, patch-clamp and quantitative reverse transcription-polymerase chain reaction techniques on right ventricular myocytes of a myocardial infarction (MI) rat model, we examined the cellular response over time. One week after MI, no sign of cellular hypertrophy was found, but action potential duration (APD) was lengthened. Both an increase in Ca2+ current (I(Ca)) and a decrease in K+ transient outward current (I(to)) underlay this effect. Consistently, the relative expression of mRNA coding for the Ca2+ channel alpha1C subunit (Ca(v)1.2) increased, and that of the K+ channel K(v)4.2 subunit decreased. Three weeks after MI, AP prolongation endured, whereas cellular hypertrophy developed. I(Ca) density, Ca(v)1.2, and K(v)4.2 mRNA levels regained control levels, but I(to) density remained reduced. Long-term treatment with RU28318, an MR antagonist, prevented this electrical remodeling. In a different etiologic model of abdominal aortic constriction, we confirmed that APD prolongation and modifications of ionic currents precede cellular hypertrophy. CONCLUSIONS: Electrical remodeling, which is triggered at least in part by MR activation, is an initial, early cellular response to hypertrophic insults.

Altered communication between L-type calcium channels and ryanodine receptors in heart failure.

Heart failure (HF) is a progressive syndrome that appears as the final phase of most cardiac diseases and is manifested as a decreased contractile function. Contraction in cardiomyocytes arises by the Ca2+ induced Ca2+ release mechanism, where Ca2+ entry (ICa) through Ca2+ channels (DHPRs) activates Ca2+ release channels (RyRs) in the junctional sarcoplasmic reticulum (SR). This is the base of cardiac excitation-contraction (EC) coupling. To elucidate the mechanisms underlying depressed function of the failing heart, analysis of EC coupling main elements have been undertaken. ICa density is usually maintained in HF. However, failing myocytes show a reduced SR Ca2+ release. Then, if the trigger of SR Ca2+ release is maintained, why is SR Ca2+ release depressed in HF? Analyses of the DHPR-RyR coupling efficiency have revealed a decrease in the ICa efficacy to trigger Ca2+ release in failing myocytes. In terminal heart failure without hypertrophy, a decrease in SR Ca2+ load can account for the decreased SR Ca2+ release. Fewer Ca2+ sparks (elementary units of SR Ca2+ release) are triggered by an equivalent ICa in hypertrophied failing myocytes, suggesting a functional or spatial reorganization of the space T-tubule junctional SR. This theory is supported by new data showing that the T-tubule density is reduced in failing cells.

Hollow multilayer photonic bandgap fibers for NIR applications.

Here we report the fabrication of hollow-core cylindrical photonic bandgap fibers with fundamental photonic bandgaps at near-infrared wavelengths, from 0.85 to 2.28 microm. In these fibers the photonic bandgaps are created by an all-solid multilayer composite meso-structure having a photonic crystal lattice period as small as 260 nm, individual layers below 75 nm and as many as 35 periods. These represent, to the best of our knowledge, the smallest period lengths and highest period counts reported to date for hollow PBG fibers. The fibers are drawn from a multilayer preform into extended lengths of fiber. Light is guided in the fibers through a large hollow core that is lined with an interior omnidirectional dielectric mirror. We extend the range of materials that can be used in these fibers to include poly(ether imide) (PEI) in addition to the arsenic triselenide (As(2)Se(3)) glass and poly(ether sulfone) (PES) that have been used previously. Further, we characterize the refractive indices of these materials over a broad wavelength range (0.25 - 15 microm) and incorporated the measured optical properties into calculations of the fiber photonic band structure and a preliminary loss analysis.

Tachycardia-induced silencing of subcellular Ca2+ signaling in atrial myocytes.

Atrial fibrillation (AF) is characterized by sustained high atrial activation rates and arrhythmogenic cellular Ca2+ signaling instability; however, it is not clear how a high atrial rate and Ca2+ instability may be related. Here, we characterized subcellular Ca2+ signaling after 5 days of high atrial rates in a rabbit model. While some changes were similar to those in persistent AF, we identified a distinct pattern of stabilized subcellular Ca2+ signaling. Ca2+ sparks, arrhythmogenic Ca2+ waves, sarcoplasmic reticulum (SR) Ca2+ leak, and SR Ca2+ content were largely unaltered. Based on computational analysis, these findings were consistent with a higher Ca2+ leak due to PKA-dependent phosphorylation of SR Ca2+ channels (RyR2s), fewer RyR2s, and smaller RyR2 clusters in the SR. We determined that less Ca2+ release per [Ca2+]i transient, increased Ca2+ buffering strength, shortened action potentials, and reduced L-type Ca2+ current contribute to a stunning reduction of intracellular Na+ concentration following rapid atrial pacing. In both patients with AF and in our rabbit model, this silencing led to failed propagation of the [Ca2+]i signal to the myocyte center. We conclude that sustained high atrial rates alone silence Ca2+ signaling and do not produce Ca2+ signaling instability, consistent with an adaptive molecular and cellular response to atrial tachycardia.

Cardiac-specific elevations in thyroid hormone enhance contractility and prevent pressure overload-induced cardiac dysfunction.

Thyroid hormone (TH) is critical for cardiac development and heart function. In heart disease, TH metabolism is abnormal, and many biochemical and functional alterations mirror hypothyroidism. Although TH therapy has been advocated for treating heart disease, a clear benefit of TH has yet to be established, possibly because of peripheral actions of TH. To assess the potential efficacy of TH in treating heart disease, type 2 deiodinase (D2), which converts the prohormone thyroxine to active triiodothyronine (T3), was expressed transiently in mouse hearts by using the tetracycline transactivator system. Increased cardiac D2 activity led to elevated cardiac T3 levels and to enhanced myocardial contractility, accompanied by increased Ca(2+) transients and sarcoplasmic reticulum (SR) Ca(2+) uptake. These phenotypic changes were associated with up-regulation of sarco(endo)plasmic reticulum calcium ATPase (SERCA) 2a expression as well as decreased Na(+)/Ca(2+) exchanger, beta-myosin heavy chain, and sarcolipin (SLN) expression. In pressure overload, targeted increases in D2 activity could not block hypertrophy but could completely prevent impaired contractility and SR Ca(2+) cycling as well as altered expression patterns of SERCA2a, SLN, and other markers of pathological hypertrophy. Our results establish that elevated D2 activity in the heart increases T3 levels and enhances cardiac contractile function while preventing deterioration of cardiac function and altered gene expression after pressure overload.

Dynamic all-optical tuning of transverse resonant cavity modes in photonic bandgap fibers.

Photonic bandgap fibers for transverse illumination containing half-wavelength microcavities have recently been designed and fabricated. We report on the fabrication and characterization of an all-optical tunable microcavity fiber. The fiber is made by incorporating a photorefractive material inside a Fabry-Perot cavity structure with a quality factor Q >200 operating at 1.5 microm. Under short-wavelength transverse external illumination, a 2 nm reversible shift of the cavity resonant mode is achieved. Dynamic all-optical tuning is reported at frequencies up to 400 Hz. Experimental results are compared with simulations based on the amplitude and kinetics of the transient photodarkening effect measured in situ in thin films.

Wavelength-scalable hollow optical fibres with large photonic bandgaps for CO2 laser transmission.

Conventional solid-core optical fibres require highly transparent materials. Such materials have been difficult to identify owing to the fundamental limitations associated with the propagation of light through solids, such as absorption, scattering and nonlinear effects. Hollow optical fibres offer the potential to minimize the dependence of light transmission on fibre material transparency. Here we report on the design and drawing of a hollow optical fibre lined with an interior omnidirectional dielectric mirror. Confinement of light in the hollow core is provided by the large photonic bandgaps established by the multiple alternating submicrometre-thick layers of a high-refractive-index glass and a low-refractive-index polymer. The fundamental and high-order transmission windows are determined by the layer dimensions and can be scaled from 0.75 to 10.6 micro m in wavelength. Tens of metres of hollow photonic bandgap fibres for transmission of carbon dioxide laser light at 10.6 micro m wavelength were drawn. The transmission losses are found to be less than 1.0 dB m(-1), orders of magnitude lower than those of the intrinsic fibre material, thus demonstrating that low attenuation can be achieved through structural design rather than high-transparency material selection.

Autonomic regulation of calcium and potassium channels is oppositely modulated by microtubules in cardiac myocytes.

We recently showed that colchicine treatment of rat ventricular myocytes increases the L-type Ca2+ current (I(Ca)) and intracellular Ca2+ concentration ([Ca2+](i)) transients and interferes with adrenergic signaling. These actions were ascribed to adenylyl cyclase (AC) stimulation after G(s) activation by alpha,beta-tubulin. Colchicine depolymerizes microtubules into alpha,beta-tubulin dimers. This study analyzed muscarinic signals in myocytes with intact or depolymerized microtubules. Myocytes were loaded with the Ca2+ indicator fluo 3 and were field stimulated at 1 Hz or voltage clamped. In untreated cells, carbachol (CCh; 1 microM) induced ACh-activated K(+) current [I(K(ACh))], which happens via betagamma-subunits from the activation of G(i). Carbachol also reduced [Ca2+](i) transients and contractions. Once G(i) is activated by muscarinic agonist, the alpha(i)-subunit is released from the betagamma-subunits, but it is silent, and its inhibition of the AC/cAMP cascade, manifested by I(Ca) reduction, is not seen unless AC has been previously activated. In colchicine-treated cells, CCh caused greater reductions of [Ca2+](i) transients and contractions than in untreated cells. The alpha(i)-subunit became effective in signaling through the AC/cAMP cascade and reduced I(Ca) without changing its voltage-dependence. Isoproterenol (Iso) regained its efficacy and reversed I(Ca) inhibition by CCh. Stimulation of I(Ca) by forskolin persisted in colchicine-treated cells when Iso was ineffective. The effect of CCh on I(K(ACh)) was occluded in colchicine-treated cells. Colchicine treatment, per se, may increase I(K(ACh)) by betagamma-subunits released from G(s) to mask this effect of CCh. Microtubules suppress I(Ca) regulation by alpha(i); their disruption releases restraints that unmask muscarinic inhibition of I(Ca). Summarily, colchicine treatment reverses regulation of ventricular excitation-contraction coupling by autonomic agents.

The role of phosphoinositide-3 kinase and PTEN in cardiovascular physiology and disease.

Phosphoinositide-3 kinases (PI3Ks) are a family of evolutionary conserved lipid kinases that mediate many cellular responses in both physiologic and pathophysiologic states. Class I PI3K can be activated by either receptor tyrosine kinase (RTK)/cytokine receptor activation (class I(A)) or G-protein-coupled receptors (GPCR) (class I(B)). Once activated PI3Ks generate phosphatidylinositols (PtdIns) (3,4,5)P(3) leading to the recruitment and activation of Akt/protein kinase B (PKB), PDK1 and monomeric G-proteins (e.g. Rac-GTPases), which then activate a range of downstream targets including glycogen synthase kinase-3beta (GSK-3beta), mammalian target of rapamycin (mTOR), p70S6 kinase, endothelial nitric oxide synthase (eNOS) and several anti-apoptotic effectors. Class I(A) (PI3Kalpha, beta and delta) and class I(B) (PI3Kgamma) PI3Ks mediate distinct phenotypes in the heart and under negative control by the 3'-lipid phosphatase, phosphatase and tensin homolog on chromosome ten (PTEN) which dephosphorylate PtdIns(3,4,5)P(3) into PtdIns(4,5)P(2). PI3Kalpha, gamma and PTEN are expressed in cardiomyocytes, fibroblasts, endothelial cells and vascular smooth muscle cells where they modulate cell survival/apoptosis, hypertrophy, contractility, metabolism and mechanotransduction. Several transgenic and knockout models support a fundamental role of PI3K/PTEN signaling in the regulation of myocardial contractility and hypertrophy. Consequently the PI3K/PTEN signaling pathways are involved in a wide variety of diseases including cardiac hypertrophy, heart failure, preconditioning and hypertension. In this review, we discuss the biochemistry and molecular biology of PI3K (class I isoforms) and PTEN and their critical role in cardiovascular physiology and diseases.