Na pump isoforms in human erythroid progenitor cells and mature erythrocytes

Abstract

This study is aimed at identifying the Na pump isoform composition of human erythroid precursor cells and mature human erythrocytes. We used purified and synchronously growing human erythroid progenitor cells cultured for 7–14 days. RNA was extracted from the progenitor cells on different days and analyzed by RT-PCR. The results showed that only the α1, α3, β2, and β3 subunit isoforms and the γ modulator were present. Northern analysis of the erythroid progenitor cells again showed that β2 but not β1 or α2 isoforms were present. The erythroid cells display a unique β subunit expression profile (called β-profiling) in that they contain the message for the β2 isoform but not β1, whereas leukocytes and platelets are known to have the message for the β1 but not for the β2 isoform. This finding is taken to indicate that our preparations are essentially purely erythroid and free from white cell contamination. Western analysis of these cultured progenitor cells confirmed the presence of α1, α3, (no α2), β2, β3, and γ together now with clear evidence that β1 protein was also present at all stages. Western analysis of the Na pump from mature human erythrocyte ghosts, purified by ouabain column chromatography, has also shown that α1, α3, β1, β2, β3, and γ are present. Thus, the Na pump isoform composition of human erythroid precursor cells and mature erythrocytes contains the α1 and α3 isoforms of the α subunit, the β1, β2, and β3 isoforms of the β subunit, and the γ modulator.