Mechanistic insights into store-operated Ca2+ entry during excitation-contraction coupling in skeletal muscle

Phasic Store-Operated Ca2+ Entry During Excitation-Contraction Coupling in Skeletal Muscle Fibers From Exercised Mice

“…In rat, EFS can trigger APs in the sealed t-system and subsequent Ca 2+ release from the SR in skinned, fast-twitch EDL muscle fibers (Posterino et al, 2000;Posterino and Lamb, 2003;Goodman et al, 2008;Launikonis et al, 2009;Koenig et al, 2018Koenig et al, , 2019. In contrast, EFS works much inferior in skinned fibers from rat and mouse slow-twitch soleus muscle and, importantly, in skinned fibers from mouse EDL muscle.…”

“…On the day of experiment animals were killed by cervical dislocation and the EDL muscle was rapidly excised. Isolation of single fibers and mechanical "skinning" of the fibers was performed as previously described (Cully et al, 2016;Koenig et al, 2018Koenig et al, , 2019. Briefly, EDL muscle was transferred to a glass petri dish filled with paraffin oil and with the bottom covered by a layer of Sylgard.…”

“…The fibers were imaged as previously described (Koenig et al, 2019), using a 20× water (Nikon, CFI APO 20× WI λS, long working distance, NA 0.95, or Plan Apo λ 20× NA 0.75) immersion objective on a Nikon laser scanning confocal microscope system (Nikon A1R+ system on an inverted Nikon Ti-E microscope) equipped with a 12 kHz resonant scanner and high-sensitivity GaAsP detectors. Rhod-5N and fluo-4 were excited at 488 and 561 nm at a laser power of 0.4-1% and 0.4-0.8%, and emitted light was collected at 525/50 nm and 595/50 nm, respectively.…”

“…Store-operated calcium entry is well understood, e.g., in the course of immune cell activation (Prakriya and Lewis, 2015), but its role in skeletal muscle remains elusive. While SOCE is a relatively slow process in non-excitable cells (Launikonis et al, 2010;Trebak et al, 2013) it presents with extraordinary fast kinetics in skeletal muscle (Launikonis and Ríos, 2007;Edwards et al, 2010;Launikonis et al, 2010;Koenig et al, 2018Koenig et al, , 2019) suggesting a close juxtaposition or even physical association of STIM1 and ORAI1 within the triads (Dirksen, 2009;Launikonis et al, 2010;Wei-Lapierre et al, 2013;Koenig et al, 2018). Recently, we demonstrated that SOCE is activated upon individual action potentials (APs) in rat skeletal muscle cells (Koenig et al, 2018(Koenig et al, , 2019, a mode of SOCE that we named phasic SOCE (pSOCE), because it showed comparable kinetics to excitation-contraction coupling.…”

ECC meets CEU—New focus on the backdoor for calcium ions in skeletal muscle cells

“…In skeletal muscle, the response of Orai1 to SR depletion is fast (less than a second; Launikonis and Ríos, 2007). It could be demonstrated, using a mechanically skinned fiber approach with a Ca 2+ indicator trapped in the sealed TTs, that the reaction is rapid enough to activate SOCE (measurable as a depletion signal) after each individual action potential in a series of excitation events (Koenig et al, 2019). Probably the rapid activation is made possible by prearranged clusters of Orai1 with a specific STIM1 splice variant (STIM1L) colocalized with RyR1 in the triad (Darbellay et al, 2011).…”