2016/05/30 by Maria Barthmes, Jun Liao, Youxing Jiang +3
Biochemistry, Genetics and Molecular Biology · Medicine · #Ion channel regulation and function #Cardiac electrophysiology and arrhythmias #Ion Transport and Channel Regulation
paper · pdf · doi:10.1085/jgp.201611587
Sodium-calcium exchangers (NCXs) are membrane transporters that play an important role in Ca(2+) homeostasis and Ca(2+) signaling. The recent crystal structure of NCXMj, a member of the NCX family from the archaebacterium Methanococcus jannaschii, provided insight into the atomistic details of sodium-calcium exchange. Here, we extend these findings by providing detailed functional data on purified NCXMj using solid supported membrane (SSM)-based electrophysiology, a powerful but unexploited tool for functional studies of electrogenic transporter proteins. We show that NCXMj is highly selective for Na(+), whereas Ca(2+) can be replaced by Mg(2+) and Sr(2+) and that NCXMj can be inhibited by divalent ions, particularly Cd(2+) By directly comparing the apparent affinities of Na(+) and Ca(2+) for NCXMj with those for human NCX1, we show excellent agreement, indicating a strong functional similarity between NCXMj and its eukaryotic isoforms. We also provide detailed instructions to facilitate the adaption of this method to other electrogenic transporter proteins. Our findings demonstrate that NCXMj can serve as a model for the NCX family and highlight several possible applications for SSM-based electrophysiology.