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.