Identification and characterization of the high affinity [3H]ryanodine receptor of the junctional sarcoplasmic reticulum Ca2+ release channel.

The high affinity ryanodine receptor of the Ca2+ release channel from junctional sarcoplasmic reticulum of rabbit skeletal muscle has been identified and characterized using monoclonal antibodies. Anti-ryanodine receptor monoclonal antibody XA7 specifically immunoprecipitated [3H]ryanodine-labeled receptor from digitonin-solubilized triads in a dose-dependent manner. [3H]Ryanodine binding to the immunoprecipitated receptor from unlabeled digitonin-solubilized triads was specific, Ca2+-dependent, stimulated by millimolar ATP, and inhibited by micromolar ruthenium red. Indirect immunoperoxidase staining of nitrocellulose blots of various skeletal muscle membrane fractions has demonstrated that anti-ryanodine receptor monoclonal antibody XA7 recognizes a high molecular weight protein (approximately 350,000 Da) which is enriched in isolated triads but absent from light sarcoplasmic reticulum vesicles and transverse tubular membrane vesicles. Thus, our results demonstrate that monoclonal antibodies to the approximately 350,000-Da junctional sarcoplasmic reticulum protein immunoprecipitated the ryanodine receptor with properties identical to those expected for the ryanodine receptor of the Ca2+ release channel.