Functional difference between SERCA2a and SERCA2b Ca2+ pumps and their modulation by phospholamban

Abstract

COS 1 cells were transfected with full-length pig stomach sarcoplasmic/endoplasmic reticulum Ca2+ pump (SERCA)2a or SERCA2b cDNA. Ca2+ uptake by microsomes from transfected cells revealed that the Ca2+ affinity of the SERCA2b Ca2+ pump (K0.5 0.17 +/- 0.01 microM) was higher than that of the SERCA2a Ca2+ pump (K0.5 0.31 +/- 0.02 microM). Thapsigargin-sensitivity was found to be identical for the two isoforms. The Ca2+ affinity of both the SERCA2a and SERCA2b Ca2+ pumps was decreased by a factor of two when they were co-expressed with phospholamban.