ANALYSIS OF MESSENGER-RNA EXPRESSION AND CLONING OF A NOVEL PLASMA-MEMBRANE CA2-ATPASE SPLICE VARIANT IN HUMAN HEART()

Four different plasma membrane Ca2+-ATPase (PMCA) genes and three sarc o(endo)plasmic reticulum Ca2+-ATPase (SERCA) genes have been previousl y cloned and characterized. In this study we have investigated the exp ression of the mRNA encoding the various PMCA and SERCA proteins in fe tal and adult human heart and placenta by the reverse-transcriptase-po lymerase-chain-reaction (RT-PCR) and cDNA cloning. We have found that PMCA1 and PMCA4 genes were expressed in 8-, 12- and 20-week fetal hear t and in adult heart. PMCA2 gene was expressed at low levels in adult heart but was not detected in fetal heart. PMCA3 mRNA was not detected in the heart nor placenta. In contrast, the mRNA encoding SERCA2a, SE RCA2b and SERCA3 were expressed in all cardiac developmental stages. M ultiple alternatively spliced mRNA transcripts which differ at splice site A and B/C of the PMCA1, PMCA2 and PMCA4 genes were detected in th e human heart. Interestingly, a novel tissue specific variant of the P MCA4 gene was detected in both fetal and adult human heart but not in placenta that accounts for about 30% of the total PMCA4 mRNA variant e xpression. DNA sequence analysis of this novel variant revealed that i t corresponds to the equivalent of the PMCA1d variant and accordingly we have named it PMCA4d. We cloned and sequenced eight cDNA inserts en coding for the PMCA1 and PMCA4 variants from a fetal human heart cDNA library confirming that these are the two main PMCA genes expressed in cardiac muscle.