Temperature acclimation has no effect on ryanodine receptor expression or subcellular localization in rainbow trout...

In cardiomyocytes, ryanodine receptors (RYRs) mediate Ca(2+)-induced Ca(2+)-release (CICR) from the sarcoplasmic reticulum (SR) during excitation-contraction (e-c) coupling. In rainbow trout heart, the relative importance of CICR increases with cold-acclimation. Thus, the aim of this study was to investigate the effect of temperature acclimation (4, 11 and 18 degrees C) on RYR intracellular localization and expression density. We used immunocytochemistry to assess intracellular localization in ventricular myocytes and Western blotting to assess RYR expression in both atrial and ventricular tissue. In ventricular myocytes, RYRs were localized peripherally in transverse bands aligning with sarcomeric m-lines and centrally around mitochondria and the nucleus. Localization did not change with temperature acclimation. RYR expression was also unaffected by temperature acclimation. The localization of RYRs at the m-line is similar to neonatal mammalian cardiomyocytes. We suggest this positioning is indicative of myocytes which rely predominantly on transsarcolemmal Ca(2+)-influx, rather than CICR, during e-c coupling.