High molecular weight proteins in the nematode C. elegans bind [3H]ryanodine and form a large conductance channel

Single-channel properties of a polypeptide fraction from the nematode Caenorhabditis elegans highly enriched in binding sites were studied in planar bilayers. [3H]Ryanodine binding sites were purified by sucrose gradient centrifugation of C. elegans microsomes solubilized in CHAPS detergent. The highest [3H]ryanodine binding activity sedimented at approximately 18% sucrose (wt/vol), and was composed of a major polypeptide with a M(r) of 360,000 and a minor polypeptide with a M(r) of 170,000. The ryanodine-binding polypeptide(s) formed a Ca(2+)-permeable channel with a permeability ratio P(divalent)/P(monovalent) = 4 and two conductance states of 215 pS and 78 pS in 0.25 M KCl. Ryanodine locked the channel in the 78 pS state and inhibited transitions between the 215 pS and 78 pS states. These data demonstrated the presence of a ryanodine receptor in C. elegans with functional properties comparable to those described in mammalian muscle.