Mitsugumin 29 regulates t-tubule architecture in the failing heart.

Transverse tubules (t-tubules) are uniquely-adapted membrane invaginations in cardiac myocytes that facilitate the synchronous release of Ca from internal stores and subsequent myofilament contraction, although these structures become disorganized and rarefied in heart failure. We previously observed that mitsugumin 29 (Mg29), an important t-tubule organizing protein in skeletal muscle, was induced in the mouse heart for the first time during dilated cardiomyopathy with heart failure. Here we generated cardiac-specific transgenic mice expressing Mg29 to model this observed induction in the failing heart.

STIM1 enhances SR Ca2+ content through binding phospholamban in rat ventricular myocytes.

In ventricular myocytes, the physiological function of stromal interaction molecule 1 (STIM1), an endo/sarcoplasmic reticulum (ER/SR) Ca(2+) sensor, is unclear with respect to its cellular localization, its Ca(2+)-dependent mobilization, and its action on Ca(2+) signaling. Confocal microscopy was used to measure Ca(2+) signaling and to track the cellular movement of STIM1 with mCherry and immunofluorescence in freshly isolated adult rat ventricular myocytes and those in short-term primary culture. We found that endogenous STIM1 was expressed at low but measureable levels along the Z-disk, in a pattern of puncta and linear segments consistent with the STIM1 localizing to the junctional SR (jSR).

Elementary calcium release events from the sarcoplasmic reticulum in the heart.

Ca(2+) release events underlie global Ca(2+) signaling yet they are regulated by local, subcellular signaling features. Here we review the latest developments of different elementary Ca(2+) release features that include Ca(2+) sparks, Ca(2+) blinks (the corresponding depletion of Ca(2+) in the sarcoplasmic reticulum (SR) during a spark) and the recently identified small Ca(2+) release events called quarky SR Ca(2+) release (QCR). QCR events arise from the opening of only a few type 2 ryanodine receptors (RyR2s) - possibly only one.

Quarky calcium release in the heart.

Rationale: 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.

Objective: 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.