Fig. 3. Immunodetection of slow MyHC2 in muscle fibers in the presence of the IP3R1 inhibitors, 2-APB and xestospongin D. Innervated (+SC) and non-innervated (–SC) PM and MA muscle fibers were cultured in control medium (–2APB/Xesto) or in medium containing 100 µM 2-APB (+2APB) or 10 µM xestospongin D (+Xesto). Muscle fibers were immunostained for fast MyHCs with monoclonal antibody F59 and Texas Red-conjugated secondary antibody and for slow MyHC2 with monoclonal antibody S58 and a fluorescein-conjugated secondary antibody. Slow MyHC2 was detected in innervated MA muscle fibers in the absence and presence of 2-APB and xestospongin D. Slow MyHC2 was detected in PM muscle fibers only in the presence of both innervation and 2-APB or innervation and xestospongin D. Bar, 50 µm.