Reconstitution of the solubilized cardiac sarcoplasmic reticulum potassium channel. Identification of a putative Mr approximately 80 kDa polypeptide constituent

Abstract

Recent evidence has indicated that potassium ion movement through sarcoplasmic reticulum (SR) K+ channels is an important countercurrent for Ca2+ release from SR. We used Chaps-solubilized SR vesicles and sucrose density gradient centrifugation to identify components of the canine cardiac SR K+ channel. To overcome the difficulty of the absence of a high-affinity specific ligand, we have successfully applied the planar lipid bilayer reconstitution technique to identify and functionally assay for the solubilized SR K+ channel. We found that Chaps solubilization of the channel did not change the protein's functional properties. The cardiac SR K+ channel sediments as a 15-20S protein complex. A polypeptide of Mr approximately 80 kDa was found to specifically comigrate with the 15-20S gradient fractions and might be a major constituent of the cardiac SR K+ channel.