This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The study of electroneutral and slow rate transporters has lagged behind the study of electrogenic transporters due to the difficulty in monitoring transport rates. Voltage clamp is used to measure currents that are proportional to transport rates in systems with a high density of electrogenic transporters that have high transport rates. This is a real-time assay for monitoring transport kinetics. Electroneutral transporters, however, do not generate current at all while slow-rate transporters generate current that is not detectable unless transporter density reaches 1-10 thousand times greater than that used with high rate electrogenic transporters. We have found that a sensitive, real-time assay for monitoring transport exists by using extracellular, electrochemical sensors to monitor gradients established during transport. By monitoring two points in the concentration gradient we can calculate flux of the analyte that is proportional to transport rate. We are exploring two separate groups of transporters in this manner, the multidrug resistance (MDR) transporters of the ATP-binding cassette (ABC) superfamily and electroneutral ion transporters, specifically the nongastric H+/K+ transporter.
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