Active Ca2+ transport in the renal tubules is thought to be mediated by two processes: a primary active process carried out by a Ca2+ activated ATPase, and a secondary active process of Na+/Ca2+ extracellular space generated by Na+, K+-ATPase. The former process is thought to be the more predominant. Characterization of the cDNAs of the plasma membrane Ca2+-ATPases revealed a family of proteins with regions of highly conserved aminoacid sequences. To examine the extent of the diversity of rat kidney plasma membrane Ca2+- ATPases, we used the polymerase chain reaction (PCR) to detect additional gene products in the rat kidney RNA that shared these conserved regions. Sequences corresponding to three previously known rat plasma membrane Ca2+ ATPases were obtained. In addition, we found sequence corresponding to a new putative plasma membrane Ca2+-ATPase, designated rat PMCA4. The objectives of this application are: to use the PCR product of the PMCA4 to screen a rat kidney cDNA library and to isolate a full length cDNA encoding for this new putative plasma membrane Ca2+-ATPase and determine its deduced aminoacid sequence. Finally, to detect specific mRNAs for PMCA4 in single nephron segments, of the rat kidney, by use of the polymerase chain reaction. These proposed studies should help answer many of the questions that exist in the understanding of the molecular basis for renal calcium transport. Furthermore, characterization of Ca2+ transport in the nephron at the molecular level may prove very useful in the investigation of such disorders of renal calcium handling as idiopathic hypercalciuria, which is frequently associated with osteoporosis and is a major cause of renal stone disease.
