Pessah_1993_Life.Sci_52_1279

[3H]Ryanodine is shown to specifically bind to cultured myotubes from 10 day quail embryo pectoralis. The binding of [3H]ryanodine increases in a time-dependent manner reaching 38 +/- 3 fmol/mg protein at 4 h. A level of theophylline (THEO; 5mM) that induces propagated wave-like contractures, doubles the capacity of the myotubes to bind [3H]ryanodine (78 +/- 7 fmol/mg protein at 4 h). Polycationic ruthenium red (100 microM) only partially inhibits (56%) [3H]ryanodine-binding, whereas the membrane permeable channel antagonist [2,6-dichloro-4-dimethyl-amino-phenyl]-isopropylamine (20 microM) inhibits occupancy > 80%. Ryanodine (10 microM) interferes with THEO-induced contractures. Pretreatment with micromolar ryanodine for 48 h, followed by washout for 48 h, causes a persistent decrease in [3H]ryanodine-binding sites. Persistent [3H]ryanodine receptor blockade coincides with a dramatic shift in AChE forms found in the myotubes. A transition from the embryonic 4S and 7S globular forms to the 20S collagen-tailed (adult) form is evident within 12 hr exposure to ryanodine and progresses after removal of the alkaloid from the culture medium, mimicking the transition that normally occurs during myocyte maturation in vivo. These results suggest that SR Ca++ movements and excitation-contraction coupling may, at least in part, contribute to AChE maturation.