Dataset Information

Quarky calcium release in the heart.

ABSTRACT: In cardiac myocytes, "Ca(2+) sparks" represent the stereotyped elemental unit of Ca(2+) release arising from activation of large arrays of ryanodine receptors (RyRs), whereas "Ca(2+) blinks" represent the reciprocal Ca(2+) depletion signal produced in the terminal cisterns of the junctional sarcoplasmic reticulum. Emerging evidence, however, suggests possible substructures in local Ca(2+) release events.With improved detection ability and sensitivity provided by simultaneous spark-blink pair measurements, we investigated possible release events that are smaller than sparks and their interplay with regular sparks.We directly visualized small solitary release events amid noise: spontaneous Ca(2+) quark-like or "quarky" Ca(2+) release (QCR) events in rabbit ventricular myocytes. Because the frequency of QCR events in paced myocytes is much higher than the frequency of Ca(2+) sparks, the total Ca(2+) leak attributable to the small QCR events is approximately equal to that of the spontaneous Ca(2+) sparks. Furthermore, the Ca(2+) release underlying a spark consists of an initial high-flux stereotypical release component and a low-flux highly variable QCR component. The QCR part of the spark, but not the initial release, is sensitive to cytosolic Ca(2+) buffering by EGTA, suggesting that the QCR component is attributable to a Ca(2+)-induced Ca(2+) release mechanism. Experimental evidence, together with modeling, suggests that QCR events may depend on the opening of rogue RyR2s (or small cluster of RyR2s).QCR events play an important role in shaping elemental Ca(2+) release characteristics and the nonspark QCR events contribute to "invisible" Ca(2+) leak in health and disease.

SUBMITTER: Brochet DX

PROVIDER: S-EPMC3036985 | biostudies-other | 2011 Jan

REPOSITORIES: biostudies-other

ACCESS DATA

Publications

Quarky calcium release in the heart.

Brochet Didier X P DX Xie Wenjun W Yang Dongmei D Cheng Heping H Lederer W Jonathan WJ

Circulation research 20101209 2

<h4>Rationale</h4>In cardiac myocytes, "Ca(2+) sparks" represent the stereotyped elemental unit of Ca(2+) release arising from activation of large arrays of ryanodine receptors (RyRs), whereas "Ca(2+) blinks" represent the reciprocal Ca(2+) depletion signal produced in the terminal cisterns of the junctional sarcoplasmic reticulum. Emerging evidence, however, suggests possible substructures in local Ca(2+) release events.<h4>Objective</h4>With improved detection ability and sensitivity provided ...[more]

PMID: 21148431

Similar Datasets

Project description:Stable calcium-induced calcium release (CICR) is critical for maintaining normal cellular contraction during cardiac excitation-contraction coupling. The fundamental element of CICR in the heart is the calcium (Ca(2+)) spark, which arises from a cluster of ryanodine receptors (RyR). Opening of these RyR clusters is triggered to produce a local, regenerative release of Ca(2+) from the sarcoplasmic reticulum (SR). The Ca(2+) leak out of the SR is an important process for cellular Ca(2+) management, and it is critically influenced by spark fidelity, i.e., the probability that a spontaneous RyR opening triggers a Ca(2+) spark. Here, we present a detailed, three-dimensional model of a cardiac Ca(2+) release unit that incorporates diffusion, intracellular buffering systems, and stochastically gated ion channels. The model exhibits realistic Ca(2+) sparks and robust Ca(2+) spark termination across a wide range of geometries and conditions. Furthermore, the model captures the details of Ca(2+) spark and nonspark-based SR Ca(2+) leak, and it produces normal excitation-contraction coupling gain. We show that SR luminal Ca(2+)-dependent regulation of the RyR is not critical for spark termination, but it can explain the exponential rise in the SR Ca(2+) leak-load relationship demonstrated in previous experimental work. Perturbations to subspace dimensions, which have been observed in experimental models of disease, strongly alter Ca(2+) spark dynamics. In addition, we find that the structure of RyR clusters also influences Ca(2+) release properties due to variations in inter-RyR coupling via local subspace Ca(2+) concentration ([Ca(2+)]ss). These results are illustrated for RyR clusters based on super-resolution stimulated emission depletion microscopy. Finally, we present a believed-novel approach by which the spark fidelity of a RyR cluster can be predicted from structural information of the cluster using the maximum eigenvalue of its adjacency matrix. These results provide critical insights into CICR dynamics in heart, under normal and pathological conditions.

Project description:In cardiac myocytes, excitation-contraction coupling depends upon sarcoplasmic reticular Ca2+ release triggered by Ca2+ influx through L-type Ca2+ channels. Although Na+-Ca2+ exchange (NCX) is essential for Ca2+ extrusion, its participation in the trigger process of excitation-contraction coupling is controversial. To investigate the role of NCX in triggering, we examined Ca2+ sparks in ventricular cardiomyocytes isolated from wild-type (WT) and cardiac-specific NCX knockout (KO) mice. Myocytes from young NCX KO mice are known to exhibit normal resting cytosolic Ca2+ and normal Ca2+ transients despite reduced L-type Ca2+ current. We loaded myocytes with fluo-3 to image Ca2+ sparks using confocal microscopy in line-scan mode. The frequency of spontaneous Ca2+ sparks was reduced in KO myocytes compared with WT. However, spark amplitude and width were increased in KO mice. Permeabilizing the myocytes with saponin eliminated differences between spontaneous sparks in WT and KO mice. These results suggest that sarcolemmal processes are responsible for the reduced spark frequency and increased spark width and amplitude in KO mice. When myocytes were loaded with 1 mM fluo-3 and 3 mM EGTA via the patch pipette to buffer diadic cleft Ca2+, the number of sparks triggered by action potentials was reduced by 60% in KO cells compared to WT cells, despite similar SR Ca2+ content in both cell types. When EGTA was omitted from the pipette solution, the number of sparks triggered in KO and WT myocytes was similar. Although the number of sparks was restored in KO cells, Ca2+ release was asynchronous. These results suggest that high subsarcolemmal Ca2+ is required to ensure synchronous triggering with short spark latency in the absence of NCX. In WT mice, high subsarcolemmal Ca2+ is not required for synchronous triggering, because NCX is capable of priming the diadic cleft with sufficient Ca2+ for normal triggering, even when subsarcolemmal Ca(2+) is lowered by EGTA. Thus, reducing subsarcolemmal Ca2+ with EGTA in NCX KO mice reveals the dependence of Ca2+ release on NCX.

Dataset Information

Quarky calcium release in the heart.

Publications

Quarky calcium release in the heart.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets