Fig. 5. Schematic of immunocytochemical staining of cultured mouse skeletal muscle. Top panels: location of myosin filaments (A-band), actin filaments (I-band), Z-line, A-band and I-band SR, and T-tubules. The overlay cartoon shows T-tubules and SR in a striated, well-differentiated myotube; this organization of T-tubules leads to the striated appearance of staining for DHPRs (Fig. 3G). In the inset the distribution of IP₃Rs is shown in green, prominent in the terminal cisternae of the I-band SR. Such a distribution would give a double-banded cross-striated pattern (Fig. 4). Bottom panel: known immunocytochemical staining patterns of selected proteins. The relationship between IP₃R staining (green) and known proteins in red: Ca²⁺ATPase (Fig. 2), -actinin, myosin and ₁ DHPR (Fig. 3). Colocalization of IP₃R (green) and the red of Ca²⁺ATPase, -actinin and ₁ DHPR results in yellow.