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

Amplitude of calcium (Ca2+) transients and width of the Sarcoplasmic Reticulum (SR) lumen in Ca2+ release units (CRUs) are significantly reduced in Calsequestrin1 (CS1)- null mice, moreover increase in fatigue resistance is characteristic of the CS1-null-model (Paolini et al 2007). We extend the study of the null model at molecular level: decrease in expression of CS2, Triadin, Sarcalumenin were detected in CS1-null FDB muscles in comparison to wild type (wt) and differential FDB (null/wt) expression of 13400 mRNAs was assayed by microarray profiling. To rescue the CS1-null phenotype, exogenous mouse CS1 was expressed in adult null-FDBs by in vivo DNA electrotransfer. CS1 expression and correct targeting to CRUs was verified by confocal microscopy, whereas restoration of CRUs architecture - i.e. shape and width of junctional SR (jSR) containing CS1 - was assessed by electron microscopy. Exogenous CS1 was correctly targeted to CRUs and positioned at the jSR, in close proximity of Ca2+ release sites. Size of the SR lumen was increased. At proteomic level CS2, Sarcalumenin, Triadin and Junctin did not change upon CS1 expression. Ca2+ transients induced by electrical stimulation were recorded in mock-transfected , and CS1-transfected fibres: successfully, average peak height and baseline showed significant increase upon CS1 expression resembling wt fibres. The present results provide strong evidences that expression of CS1 directly controls size of jSR terminal cisternae, influences resting cytosolic Ca2+ and modulates the amplitude of Ca2+ transient in response to electrical stimulation in fast-twitch muscles.Paolini, C et al. 2007 J Physiol, 583: 767.