In vivo monitoring of Ca2+ uptake into mitochondria of mouse skeletal muscle during contraction

Abstract

Although the importance of mitochondria in patho-physiology has become increasingly evident, it remains unclear whether these organelles play a role in Ca2+ handling by skeletal muscle. This undefined situation is mainly due to technical limitations in measuring Ca2+ transients reliably during the contraction–relaxation cycle. Using two-photon microscopy and genetically expressed “cameleon” Ca2+ sensors, we developed a robust system that enables the measurement of both cytoplasmic and mitochondrial Ca2+ transients in vivo. We show here for the first time that, in vivo and under highly physiological conditions, mitochondria in mammalian skeletal muscle take up Ca2+ during contraction induced by motor nerve stimulation and rapidly release it during relaxation. The mitochondrial Ca2+ increase is delayed by a few milliseconds compared with the cytosolic Ca2+ rise and occurs both during a single twitch and upon tetanic contraction.

Deficiency in parvalbumin, but not in calbindin D-28k upregulates mitochondrial volume and decreases smooth endoplasmic reticulum surface selectively in a peripheral, subplasmalemmal region in the soma of Purkinje cells

“…Similarly, mitochondria have experienced a comeback as transient Ca 2ϩ stores also under physiological conditions (Pozzan and Rizzuto, 2000), contrasting the earlier view that these organelles contribute to Ca 2ϩ homeostasis primarily under pathologic conditions (excitotoxicity, apoptosis). Mitochondria participate in Ca 2ϩ removal during muscle relaxation in slow-twitch (Sembrowich et al, 1985;Gillis, 1997) and fast-twitch muscles (Rudolf et al, 2004); in neurons they also contribute to the presynaptic regulation of Ca 2ϩ transients (Billups and Forsythe, 2002). Besides the anticipated slowing of muscle relaxation in PVϪ/Ϫ mice, a twofold increase in mitochondrial volume density is observed that is viewed as a specific homeostatic compensation mechanism (Chen et al, 2001).…”

Physical Coupling Supports the Local Ca2+ Transfer between Sarcoplasmic Reticulum Subdomains and the Mitochondria in Heart Muscle

“…We have recently demonstrated that the local Ca 2ϩ coupling is regulated by the spacing between the ER and outer mitochondrial membrane and that the ER-mitochondrial interface is secured by protein tethers (8). Local [Ca 2ϩ ] regulation has also been shown to support the Ca 2ϩ signal propagation from the ryanodine receptors (RyR, the phylogenetic ancestors of the inositol 1,4,5-trisphosphate receptor) to the mitochondria in cardiac muscle cells (9,10) and in skeletal muscle (11)(12)(13). However, whether the local Ca 2ϩ communication between the SR and mitochondria is supported by physical coupling is yet to be elucidated.…”

Mitochondrial Calcium Uptake Regulates Rapid Calcium Transients in Skeletal Muscle during Excitation-Contraction (E-C) Coupling

“…Recently, organelle-targeted Ca 2ϩ biosensors have been developed to directly monitor Ca 2ϩ inside the SR or mitochondria in skeletal muscle fibers (27,28). We utilized the biosensor protein YC3.6, which displays an improved dynamic range (13) when compared with the earlier version (YC2) (28).…”