A new functional analysis of intracellular ion-transporting proteins

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A novel electrophysiological assay technique based on solid supported membranes (SSM) has been shown to be useful for analysis of channels and transporters. We tried to apply this technique to synaptic vesicles (SVs) and lysosomal membranes (LMs), purified from rat brains and mouse livers, respectively. Application of ATP to the sensors with SVs triggered current responses dependent on Mg2+ and sensitive to bafilomycin A1 (Baf), which are thought to be V-ATPase specific currents. On the other hand, though LMs are also embedded with V-ATPases, the sensors evoked current responses with different characteristics. They were independent of Mg2+, only partially sensitive to Baf and even triggered by application of ADP. These features suggest that the currents are not attributed to V-ATPases but any other lysosomal protein. The present study shows the utility and potential of SSM-based electrophysiology especially for analyzing native organellar membrane proteins.