Studies done many years ago established unequivocally the key role of calcium as a universal second messenger. In contrast, the second messenger roles of reactive oxygen and nitrogen species have emerged only recently. Therefore, their contributions to physiological cell signaling pathways have not yet become universally accepted, and many biological researchers still regard them only as cellular noxious agents. Furthermore, it is becoming increasingly apparent that there are significant interactions between calcium and redox species, and that these interactions modify a variety of proteins that participate in signaling transduction pathways and in other fundamental cellular functions that determine cell life or death. This review article addresses first the central aspects of calcium and redox signaling pathways in animal cells, and continues with the molecular mechanisms that underlie crosstalk between calcium and redox signals under a number of physiological or pathological conditions. To conclude, the review focuses on conditions that, by promoting cellular oxidative stress, lead to the generation of abnormal calcium signals, and how this calcium imbalance may cause a variety of human diseases including, in particular, degenerative diseases of the central nervous system and cardiac pathologies.

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SUMMARY1. The fluorescent Na' indicator SBFI was incorporated into isolated ventricular myocytes using the acetoxymethyl (AM) ester. 2. The excitation spectrum was found to be shifted about 20 nm in the cell compared to in vitro. In the cell, an increase of [Na+] decreased fluorescence at 380 nm (F380) and had no effect at 340 nm (F340). The ratio (R = F340/F380) was used as a measure of [Na+]

We have analyzed the effects of the endogenous redoxactive agents S-nitrosoglutathione and glutathione disulfide, and the NO donor NOR-3, on calcium release kinetics mediated by ryanodine receptor channels. Incubation of triad-enriched sarcoplasmic reticulum vesicles isolated from mammalian skeletal muscle with these three agents elicits different responses. Glutathione disulfide significantly reduces the inhibitory effect of Mg 2؉ without altering Ca 2؉ activation of release kinetics, whereas NOR-3 enhances Ca 2؉ activation of release kinetics without altering Mg 2؉ inhibition. Incubation with S-nitrosoglutathione produces both effects; it significantly enhances Ca 2؉ activation of release kinetics and diminishes the inhibitory effect of Mg 2؉ on this process. Triad incubation with [ 35 S]nitrosoglutathione at pCa 5 promoted 35 S incorporation into 2.5 cysteine residues per channel monomer; this incorporation decreased significantly at pCa 9. These findings indicate that S-nitrosoglutathione supports S-glutathionylation as well as the reported S-nitrosylation of ryanodine receptor channels (Sun, J., Xu, L., Eu, J. P., Stamler, J. S., and Meissner, G. (2003) J. Biol. Chem. 278, 8184 -8189). The combined results suggest that S-glutathionylation of specific cysteine residues can modulate channel inhibition by Mg 2؉ , whereas S-nitrosylation of different cysteines can modulate the activation of the channel by Ca 2؉ . Possible physiological and pathological implications of the activation of skeletal Ca 2؉ release channels by endogenous redox species are discussed. Ca 2ϩ -induced Ca 2ϩ release (CICR) 1 mediated by ryanodine receptors/Ca 2ϩ release channels (RyR channels) has a central role in very dissimilar processes. Among other processes, CICR mediates muscle contraction, neuronal plasticity, and secretion (1-4). Not surprisingly, these Ca 2ϩ release channels are extensively regulated by a variety of endogenous ions and molecules, as well as through interactions with other proteins (3,(5)(6)(7)(8).During the last 15 years, increasing evidence has accumulated supporting redox modulation of RyR channels (for reviews, see Refs. 9 -11). Each of the four homologous 565-kDa protein subunits of the skeletal muscle type 1 ryanodine receptor channel (RyR1 channel) contains 100 cysteine residues (12). In the native channel, ϳ50 of these residues appear to be in the reduced state, and, of these, ϳ10 -12 are highly susceptible to oxidation/modification by exogenous sulfhydryl (SH) reagents (13). Sulfhydryl modification enhances Ca 2ϩ release from skeletal SR vesicles (14 -20) and activates RyR1 channels incorporated in planar lipid bilayers (18,(21)(22)(23)(24)(25)(26). Sulfhydryl modification also increases [ 3 H]ryanodine binding to skeletal SR membranes (18,21,24,27). Highly reactive SH residues of the RyR1 channel protein participate in interactions between homotetrameric channel subunits (24), participate in the formation of high molecular weight complexes with triadin (29, 30), and modulate calmodulin binding to the cha...

SUMMARY1. Fluorescence measurements have been made in single, isolated rat ventricular myocytes using the Ca2+-sensitive indicators Fura-2 and Indo-1. In Fura-2-loaded cells, the application of caffeine (2-20 mM)

The loss of cardioprotection induced by the NADPH oxidase inhibitor suggests that ROS generated by this enzyme are important mediators of the preconditioning response, which presumably involves NADPH oxidase-induced RyR2 S-glutathionylation.

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Calcium release through cardiac ryanodine receptors (RyR2) triggers heart muscle contraction. Reactive oxygen/nitrogen species (ROS/RNS), normally produced in the heart, promote endogenous RyR2 S-nitrosylation and S-glutathionylation. These reversible redox modifications increase RyR2 activity in vitro, and presumably also in vivo. RyR2 S-glutathionylation increases under physiologically relevant conditions (tachycardia and exercise), suggesting that cardiac cells utilize this redox modification to increase RyR2 activity under increased demand. In contrast, in vivo changes in RyR2 S-nitrosylation in response to physiological stimuli remain uncharacterized. The number and identity of the highly reactive RyR2 cysteine residues and the nature of the redox modification they undergo are presently unknown. Likewise, the physiological sources of ROS/RNS responsible for functionally relevant RyR2 redox modifications have not been completely identified. The redox state of RyR2 is altered in heart failure leading to enhanced RyR2 activity, which presumably contributes to decrease SR calcium content and induce other calcium release abnormalities observed in heart failure. Greater understanding of RyR2 redox modulation is necessary to counteract the deleterious consequences of RyR2 activity deregulation caused by oxidative stress.