Expression Of Calsequestrin-1 (CS1) In CS1-null Mice: Restoration Of Ca2+ Release Unit Architecture And Amplitude Of Ca2+ Transient In Fast-twitch Muscle Fibres

Abstract

the procedure. The other electrode was used to dialyze the fiber with a solution containing either 6-15 mM BAPTA, or up to 60 mM EGTA (pCa¼7.0), and adjusted to pH¼7.0 with 20 or 60 mM MOPS, respectively. Free myoplasmic Ca 2þ concentration ([Ca 2þ ]) changes were measured with the low affinity indicator OGB-5N (200 mM). SR Ca 2þ release was elicited by either 20 mM caffeine, or 1 mM 4-chloro-methy-phenol (4CmC), added to the external solution. The maximal fluorescence change of the Ca 2þ indicator was assessed at the end of the protocol by exposing the fibers to saponin (0.1 mg/ml in isotonic CaCl 2 , pH¼7.0 with 20 mM MOPS). To prevent changes in shape of the fibers under these conditions, they were pretreated for 1 min with 1% formaldehyde (in Tyrode). The experiments were conducted at 20 C. A single model compartment was used to estimate (from the [Ca 2þ ] changes) the total Ca 2þ released in response to caffeine/4CmC application. We obtained values of SR Ca 2þ content in the range of 15-27 mM for normal FDB fibers. Interestingly, comparable values were obtained in fibers from mdx mice.

Sequential stages in the age-dependent gradual formation and accumulation of tubular aggregates in fast twitch muscle fibers: SERCA and calsequestrin involvement

“…First, a net accumulation CASQ has been directly demonstrated by western blotting in muscle presenting TAs (Chevessier et al 2004). Second, experimental overexpression of CASQ2 and CASQ1, respectively, in cardiac (Tijskens et al 2003;Sato et al 1998) and skeletal (Tomasi et al 2009) muscle, results in swelling of the SR, which appear filled by an electron dense polymer. The initial accumulation of CASQ in I band SR is likely not a direct cause of TAs' formation, since CASQ accumulation occurs in both male and female mice (Chevessier et al 2004), but TAs are present only in the former and overexpression of CASQ (see references above) does not lead to TA formation.…”