Fig. 4. IP₃R in double cross striations and in the nuclear envelope region of cultured mouse myotubes; single optical sections, 530±53 nm. Top panel: IP₃R staining is distributed in double cross striations (two striations per sarcomere) in a highly differentiated myotube. A connection between the cross striations of IP₃Rs of the SR and the IP₃Rs of the nuclear envelope region is suggested. Bottom panel shows another cell in which the continuity of SR and nuclear region IP₃R staining is most evident (arrowheads). The orange tones represent the glow-over-under function of the microscope.