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The article provides information on the research study entitled, "Calcium Sparks." The discovery of calcium sparks and other related family of calcium signaling events exposed the basic principles of signal system of calcium. Calcium sparks are involved in cardiac and skeletal muscle excitation-contraction, regulation vascular tone, membrane excitability, and secretions of neurons. Investigation found out possible effects of calcium sparks in cardiovascular diseases.

Flash photolysis of “caged” compounds using ultraviolet light is a powerful experimental technique for producing rapid changes in concentrations of bioactive signaling molecules. Studies that employ this technique have used diverse strategies for controlling the spatial and temporal application of light to the specimen. In this paper, we describe a new system for flash photolysis that delivers light from a pulsed, adjustable intensity laser through an optical fiber coupled into the epifluorescence port of a commercial confocal microscope. Photolysis is achieved with extremely brief (5 ns) pulses of ultraviolet light (355 nm) that can be synchronized with respect to confocal laser scanning. The system described also localizes the UV intensity spatially so that uncaging only occurs in defined subcellular regions; moreover, because the microscope optics are used in localization, the photolysis volume can be easily adjusted. Experiments performed on rat ventricular myocytes loaded with the Ca2+ indicator fluo-3 and the Ca2+ cage o-nitrophenyl ethylene glycol bis(2-aminoethyl ether)- N, N, N′ N′-tetraacetic acid (NP–EGTA) demonstrate the system’s capabilities. Localized intracellular increases in [Ca2+] can trigger sarcoplasmic reticular Ca2+ release events such as Ca2+ sparks and, under certain conditions, regenerative Ca2+ waves. This relatively simple and inexpensive system is, therefore, a useful tool for examining local signaling in the heart and other tissues. [ABSTRACT FROM AUTHOR]

Excitation–contraction coupling in the heart depends on the positive feedback process of Ca2+-induced Ca2+ release (CICR). While CICR provides for robust triggering of Ca2+ sparks, the mechanisms underlying their termination remain unknown. At present, it is unclear how a cluster of Ca2+ release channels (ryanodine receptors or RyRs) can be made to turn off when their activity is sustained by the Ca2+ release itself. We use a novel experimental approach to investigate indirectly this issue by exploring restitution of Ca2+ sparks. We exploit the fact that ryanodine can bind, nearly irreversibly, to an RyR subunit (monomer) and increase the open probability of the homotetrameric channel. By applying low concentrations of ryanodine to rat ventricular myocytes, we observe repeated activations of individual Ca2+ spark sites. Examination of these repetitive Ca2+ sparks reveals that spark amplitude recovers with a time constant of 91 ms whereas the sigmoidal recovery of triggering probability lags behind amplitude recovery by∼80 ms. We conclude that restitution of Ca2+ sparks depends on local refilling of SR stores after depletion and may also depend on another time-dependent process such as recovery from inactivation or a slow conformational change after rebinding of Ca2+ to SR regulatory proteins. [ABSTRACT FROM AUTHOR]

ß-Adrenergic receptor (ßAR) stimulation increases cytosolic Ca2+ to physiologically augment cardiac contraction, whereas excessiveßAR activation causes adverse cardiac remodeling, including myocardial hypertrophy, dilation and dysfunction, in individuals with myocardial infarction. The Ca2+-calmodulin-dependent protein kinase II (CaMKII) is a recently identified downstream element of theßAR-initiated signaling cascade that is linked to pathological myocardial remodeling and to regulation of key proteins involved in cardiac excitation-contraction coupling. We developed a genetic mouse model of cardiac CaMKII inhibition to test the role of CaMKII inßAR signaling in vivo. Here we show CaMKII inhibition substantially prevented maladaptive remodeling from excessiveßAR stimulation and myocardial infarction, and induced balanced changes in excitation-contraction coupling that preserved baseline andßAR-stimulated physiological increases in cardiac function. These findings mark CaMKII as a determinant of clinically important heart disease phenotypes, and suggest CaMKII inhibition can be a highly selective approach for targeting adverse myocardial remodeling linked toßAR signaling. [ABSTRACT FROM AUTHOR]

Intracellular cardiac Ca[sup 2+] handling involves interactions of numerous distinct cellular and macromolecular structures. Such interactions coordinate the complicated behaviors of individual processes into spatial and temporal coherent patterns of Ca[sup 2+] sparks, oscillations and traveling waves. Understanding the dynamical behaviors and functional roles of intracellular Ca[sup 2+] handling requires not only detailed experimental information about subcellular structures and dynamics, but also useful tools to integrate and analyze this information. This requires interactions between experimental and simulation results within a virtual cell. [ABSTRACT FROM AUTHOR]

Introduction: The purpose of this study was to examine the electrophysiologic derangements that underlie contractile failure in single human heart muscle cells exposed to metabolic inhibition. Methods and Results: Single myocytes were isolated from right atrial appendage specimens obtained intraoperatively from patients undergoing routine cardiac surgery. On exposure to 10-mM 2-deoxyglucose (to inhibit glycolysis) and 2-mM cyanide (to inhibit oxidative phosphorylation), twitch shortening decreased to undetectable levels over 5-6 minutes. The action potential duration declined in parallel with the contractile failure. Using voltage clamp depolarizations of a fixed duration the twitch was maintained in metabolic blockade until the development of maintained (rigor) contracture. At this time a large increase in K+ conductance, which can be attributed to the activation of ATP-sensitive K+ channels (KATP channels), was measured. In isolated inside-out membrane patches, the ATP dependence of KATP channel activity was described by a sigmoid curve with K1,ATP (ATP concentration required for half-maximal inhibition of KATP channel activity) = 8 µM and Hill coefficient (nH) = 1.2. The single channel current-voltage relationship reversed close to the K+ equilibrium potential and the conductance was approximately linear (g = 29 pS) over the voltage range included in the action potential (-60 mV to + 20 mV). Conclusion: In human atrial cardiac myocytes subjected to complete metabolic inhibition, contractile failure is caused by action potential shortening resulting from an increase in K+ conductance presumably through the activation of KATP channels. [ABSTRACT FROM AUTHOR]