The following resources related to this article are available online at http://stke.sciencemag.org. Reactive oxygen species (ROS) are involved in many physiological and pathophysiological cellular processes. We used lymphocytes, which are exposed to highly oxidizing environments during inflammation, to study the influence of ROS on cellular function. Calcium ion (Ca 2+ ) influx through Ca 2+ release-activated Ca 2+ (CRAC) channels composed of proteins of the ORAI family is essential for the activation, proliferation, and differentiation of T lymphocytes, but whether and how ROS affect ORAI channel function have been unclear. Here, we combined Ca 2+ imaging, patch-clamp recordings and measurements of cell proliferation and cytokine secretion to determine the effects of hydrogen peroxide (H 2 O 2 ) on ORAI channel activity and human T helper lymphocyte (T H cell) function. ORAI1, but not ORAI3, channels were inhibited by oxidation by H 2 O 2 . The differential redox sensitivity of ORAI1 and ORAI3 channels depended mainly on an extracellularly located reactive cysteine, which is absent in ORAI3. T H cells became progressively less redox-sensitive after differentiation into effector cells, a shift that would allow them to proliferate, differentiate, and secrete cytokines in oxidizing environments. The decreased redox sensitivity of effector T H cells correlated with increased expression of Orai3 and increased abundance of several cytosolic antioxidants. Knockdown of ORAI3 with small-interfering RNA rendered effector T H cells more redox-sensitive. The differential expression of Orai isoforms between naïve and effector T H cells may tune cellular responses under oxidative stress. Article Toolshttp INTRODUCTION Intracellular Ca2+ is a second messenger involved in the regulation of a diverse range of functions (1). One of the major Ca 2+ entry pathways into nonexcitable cells, such as lymphocytes and epithelial cells, is through ubiquitously expressed Ca 2+ release-activated Ca 2+ (CRAC) channels that are localized in the plasma membrane. Ca 2+ influx through CRAC channels is activated when inositol 1,4,5-trisphosphate (IP 3 ) triggers Ca 2+ release from intracellular stores in the lumen of the endoplasmic reticulum (ER) (2-4).The concomitant decrease in ER luminal Ca 2+ triggers accumulation of the ER Ca 2+ sensor protein stromal interaction molecule (STIM1) into puncta close to the plasma membrane (5, 6). These clustered STIM1 proteins directly activate Ca 2+ influx through CRAC channels, which are encoded by the Orai gene family (7-11). ORAI proteins contain four transmembrane domains with both N-and C-terminal intracellular domains (12, 13) that contain putative N-terminal calmodulinbinding domains and C-terminal coiled-coil motifs. Orai family members are highly homologous, and Orai1 and 3 are widely expressed at the messenger RNA (mRNA) level, with Orai2 showing a somewhat more restricted expression pattern (14, 15). ORAI1 proteins contain the longest intracellular N termini with two proline-rich regions an...

Mouse pancreatic islets were used to investigate the mechanisms and functional significance of the B cell membrane depolarization by acetylcholine (ACh). At low glucose (3mM), ACh (20 microM) increased 22Na+ influx, and slightly depolarized the B cell membrane but did not induce electrical activity or stimulate 45Ca2+ influx. ACh also accelerated 86Rb+ and 45Ca2+ efflux and barely affected basal insulin release. At a stimulatory concentration of glucose (10 mM), ACh stimulated 22Na+ influx, depolarized the B cell membrane, increased glucose-induced electrical activity, and stimulated 45Ca2+ influx. ACh also accelerated 86Rb+ and 45Ca2+ efflux and strongly potentiated insulin release. Omission of extracellular Ca2+ did not impair ACh stimulation of 22Na+ influx or 86Rb+ efflux, slightly modified the acceleration of 45Ca2+ efflux, and almost completely suppressed the increase in insulin release. Na+ omission (with N-methyl-D-glucamine as substitute) prevented the B cell membrane depolarization and the stimulation of 45Ca2+ influx, largely inhibited the acceleration of 86Rb+ efflux and insulin release, and suppressed the late phase of 45Ca2+ efflux otherwise produced by ACh. On the other hand, ACh stimulation of 3H efflux from islets prelabeled with myo-[2-3H]inositol was not affected by Na+ omission. All effects of ACh were blocked by atropine and unaffected by nicotinic antagonists. It is concluded that activation of muscarinic receptors depolarized the B cell membrane by increasing its permeability to Na+. When the membrane is already depolarized by glucose, this further depolarization augments Ca2+ influx and, hence, potentiates insulin release.

The phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) was used to study the effects of protein kinase C activation on stimulus-secretion coupling in mouse pancreatic B-cells. At a nonstimulatory concentration of glucose (3 mM), 100 nM TPA, but not 10 nM TPA, slightly and slowly increased insulin release and 45Ca2+ efflux and decreased 86Rb+ efflux, but did not affect the membrane potential of B-cells. At a threshold concentration of glucose (7 mM), 100 nM TPA markedly increased insulin release without triggering electrical activity in B-cells. At a stimulatory concentration of glucose (10 mM), TPA caused a dose-dependent irreversible increase in insulin release, 45Ca2+ efflux, and 86Rb+ efflux and slightly augmented islet cAMP levels. Omission of extracellular Ca2+ abolished the effects of 10 nM TPA and partially inhibited those of 100 nM TPA on insulin release and 45Ca2+ efflux. In contrast, their effect on 86Rb+ efflux was paradoxically augmented. Glucose-induced electrical activity in B-cells was only marginally affected by TPA; the duration of the slow waves with spikes was not modified, but a small shortening of the polarized intervals raised their frequency and slightly increased the overall activity. This increase was significant only with 10 nM TPA, whereas only 100 nM TPA brought about a minute increase in 45Ca2+ influx. These results thus show that TPA induces insulin release or potentiates glucose-induced insulin release without mimicking or amplifying the initial ionic and electrical signals triggered by glucose. They suggest that protein kinase C activation affects stimulus-secretion coupling by modulating intracellular and/or nonelectrogenic membrane events.

Reactive oxygen species (ROS) exhibit different spatial and temporal distributions as well as concentrations in-and outside the cell, thereby functioning as signaling or pathogen-destroying molecules. Especially the ROS H 2 O 2 is important for the patho/physiological status of an organism. Electrochemistry (EM) and electron spin resonance (ESR)-based techniques allow quantification of H 2 O 2 in artificial and living systems, coping a concentration range from low nM up to mM. Working electrodes for EM are optimized by diverse modifications and, additionally, redox mediators are used. Ultramicroelectrodes allow scanning of single cells to spatially resolve and quantify extracellular H 2 O 2 in real-time. With ESR spectroscopy, • O 2¯, but not H 2 O 2 , can be directly determined by spin probes in-and outside of cells in suspensions. Monitoring H 2 O 2 requires formation of intermediate radicals, detectable with spin probes. Low μM [H 2 O 2 ] can thus be assessed specifically. Using suitable spin traps, in-vivo ESR and immuno-spin trapping can visualize different radicals at their respective production sites in small animals, organs and tissues. Here, the redox reaction cascades may interfere with cell metabolism. Optimization of all methods established for H 2 O 2 determination would be favorable to finally combine them for mutual validation. Thus, a deeper insight into cellular ROS metabolism can be obtained.