Fig. 1. Immunodetection of IP3R1 in fast and slow muscle fibers. Embryonic day 13 (E13) pectoralis major and medial adductor myoblasts were isolated, cultured, and allowed to differentiate into muscle fibers for 7 days. On day 3 of incubation, E5 chick spinal cords were added to some of the cultures (+SC). Other cultures lacked innervation (–SC). IP3R1 was detected with a rabbit anti-IP3R1 antibody (+IP3R Ab) and a fluorescein-conjugated (green) secondary antibody. Control cultures lacked addition of the IP3R1 primary antibody (–IP3R Ab), but were incubated with the fluorescein-conjugated secondary antibody. Addition of spinal cords to muscle fiber cultures generates clusters of acetylcholine receptors in muscle fibers, which were detected by addition of rhodamine-conjugated (red) -bungarotoxin. Bar, 50 µm.