Purification and characterization of the inositol 1,4,5-trisphosphate receptor protein from rat vas deferens

Among rat peripheral tissues examined, Ins(1,4,5)P₃ receptor binding is highest in the vas deferens, with levels about 25% of those of the cerebellum. We have purified the InsP₃ receptor binding protein from rat vas deferens membranes 600-fold. The purified protein displays a single 260 kDa band on SDS/PAGE, and the native protein has an apparent molecular mass of 1000 kDa, the same as in cerebellum. The inositol phosphate specificity, pH-dependence and influence of various reagents are the same for purified vas deferens and cerebellar receptors. Whereas particulate InsP₃ binding in cerebellum is potently inhibited by Ca²⁺, particulate and purified vas deferens receptor binding of InsP₃ is not influenced by Ca²⁺. Vas deferens appears to lack calmedin activity, but the InsP₃ receptor is sensitive to Ca²⁺ inhibition conferred by brain calmedin. The vas deferens may prove to be a valuable tissue for characterizing functional aspects of InsP₃ receptors.