Mice Null for Calsequestrin 1 Exhibit Deficits in Functional Performance and Sarcoplasmic Reticulum Calcium Handling

Abstract

In skeletal muscle, the release of calcium (Ca2+) by ryanodine sensitive sarcoplasmic reticulum (SR) Ca2+ release channels (i.e., ryanodine receptors; RyR1s) is the primary determinant of contractile filament activation. Much attention has been focused on calsequestrin (CASQ1) and its role in SR Ca2+ buffering as well as its potential for modulating RyR1, the L-type Ca2+ channel (dihydropyridine receptor, DHPR) and other sarcolemmal channels through sensing luminal [Ca2+]. The genetic ablation of CASQ1 expression results in significant alterations in SR Ca2+ content and SR Ca2+ release especially during prolonged activation. While these findings predict a significant loss-of-function phenotype in vivo, little information on functional status of CASQ1 null mice is available. We examined fast muscle in vivo and in vitro and identified significant deficits in functional performance that indicate an inability to sustain contractile activation. In single CASQ1 null skeletal myofibers we demonstrate a decrease in voltage dependent RyR Ca2+ release with single action potentials and a collapse of the Ca2+ release with repetitive trains. Under voltage clamp, SR Ca2+ release flux and total SR Ca2+ release are significantly reduced in CASQ1 null myofibers. The decrease in peak Ca2+ release flux appears to be solely due to elimination of the slowly decaying component of SR Ca2+ release, whereas the rapidly decaying component of SR Ca2+ release is not altered in either amplitude or time course in CASQ1 null fibers. Finally, intra-SR [Ca2+] during ligand and voltage activation of RyR1 revealed a significant decrease in the SR[Ca2+]free in intact CASQ1 null fibers and a increase in the release and uptake kinetics consistent with a depletion of intra-SR Ca2+ buffering capacity. Taken together we have revealed that the genetic ablation of CASQ1 expression results in significant functional deficits consistent with a decrease in the slowly decaying component of SR Ca2+ release.

Enhanced dihydropyridine receptor calcium channel activity restores muscle strength in JP45/CASQ1 double knockout mice

“…4b, arrow middle panel ‘first’). The reduction of force development during trains of action potentials is most likely indicative of poor calcium buffering capacity of SR caused by the ablation of CASQ1, as a similar inability to sustain muscle contraction has been observed in muscles from CASQ1 KO mice 24 but not in the EDL muscles from JP45 KO mice 27 , which have a normal CASQ1 expression level. Ablation of JP45 in a CASQ1 KO background has a remarkable effect on the peak tension after repetitive tetanic trains at 0.27 Hz.…”

The couplonopathies: A comparative approach to a class of diseases of skeletal and cardiac muscle

“…Consider first the phenotype of calsequestrin 1– and triadin-null mice. Calsequestrin 1–null mice ( Paolini et al, 2007 ) have moderate muscle weakness and characteristic changes in cytosolic Ca 2+ transients, caused by loss of Ca storage capacity ( Canato et al, 2010 ; Olojo et al, 2011 ). 4 Triadin-null mice ( Shen et al, 2007 ; Oddoux et al, 2009 ), which lack all skeletal and cardiac products of the single triadin gene, combine a cardiac phenotype of CPVT and a skeletal phenotype of weakness, together with a sharply reduced expression of calsequestrin 1.…”

A better method to measure total calcium in biological samples yields immediate payoffs

“…Consistent with this possibility, Sztretye et al (2011) found an 18% greater average value for [Ca 2+ ] SR in cells of calsequestrin 1–null mice compared with those of wild-type mice (a difference that was not statistically significant). The observation of greater force and rate of force development in twitches of low frequency in calsequestrin-null mice points in the same direction ( Olojo et al, 2011 ). In contrast, Canato et al (2010) found no difference.…”

“…In the present work, ablation of calsequestrin reduced total calcium concentration in the fast-twitch EDL muscle by 38%. This result, however, was reached after taking into account the substantial difference in weight between wild-type and calsequestrin-null muscles (a difference documented by Olojo et al, 2011 ). Indeed, the actual calcium concentration, in millimoles per kilogram of muscle, was not different between wild type and null.…”