The activity of the Na+-Ca2+ exchanger, a membrane transporter that mediates Ca2+ efflux, has been described in amphibian and mammalian renal proximal tubules. However, demonstration of cell-specific expression of the Na+-Ca2+ exchanger in proximal renal tubules has been restricted to functional assays. In this work, Na+-Ca2+ exchanger gene expression in rat proximal tubules was characterized by three additional criteria: functional assay of transport activity in membrane vesicles derived from proximal tubules, expression of specific Na+-Ca2+ exchanger protein detected on Western blots, and determination of specific mRNA encoding Na+-Ca2+ exchanger protein on Northern blots. A new transport activity assay showed that proximal tubule membranes contained the highest Na+-Ca2+ exchanger transport activity reported in renal tissues. In dog renal proximal tubules and sarcolemma, a specific protein of ~70 kDa was detected, whereas in rat proximal tubules and sarcolemma, the specific protein approximated 65 kDa and was localized to the basolateral membrane. On Northern blots, a single 7-kb transcript isolated from rat proximal tubules, whole kidney, and heart hybridized under high-stringency conditions with rat heart cDNA. These data indicate that Na+-Ca2+ exchanger protein expressed in rat proximal tubule is similar, if not identical, to the cardiac protein. We suggest that the tubular Na+-Ca2+ exchanger characterized herein represents the Na+-Ca2+ exchanger described in functional assays of renal proximal tubules.
|Original language||English (US)|
|Journal||American Journal of Physiology - Renal Fluid and Electrolyte Physiology|
|Issue number||5 32-5|
|State||Published - Jan 1 1992|
- calcium efflux
- sodium-calcium exchanger
ASJC Scopus subject areas