cDNA cloning of a renal Na⁺-Ca²⁺ exchanger

In the present study, the polymerase chain reaction (PCR) and library screening were used to clone a cDNA for a rabbit kidney Na⁺-Ca²⁺ exchanger on the basis of homology with the canine cardiac sarcolemmal sequence (D. A. Nicoll, S. Longoni, and K. D. Philipson. Science Wash. DC 250: 562-565, 1990). There is a high degree of similarity between the two sequences, with nucleotide identities of 95, 89, and 90% in the hydrophobic membrane- associated domain, cytoplasmic domain, and 3'-untranslated region, respectively. The rabbit kidney cDNA encodes a predicted protein of 941 amino acids, 29 amino acids shorter than the canine sequence, with a relative molecular weight of 105,121. The deduced amino acid sequence is 96% identical in the membrane-associated domain and 94% identical in the cytoplasmic domain. Northern blot analysis reveals that the cDNA is expressed in the renal cortex. No expression is detected in the medulla. This result is in agreement with micropuncture studies that show Na⁺-Ca²⁺ exchanger activity in cortical but not medullary nephron segments.