Three differentially expressed Na,K-ATPase alpha subunit isoforms: structural and functional implications.

Abstract

Abstract. We have characterized cDNAs coding for three Na,K-ATPase tx subunit isoforms from the rat, a species resistant to ouabain. Northern blot and Sl-nuclease mapping analyses revealed that these a subunit mRNAs are expressed in a tissue-specific and developmentally regulated fashion. The mRNA for the al isoform, --~-4.5 kb long, is expressed in all fetal and adult rat tissues examined. The a2 mRNA, also ---4.5 kb long, is expressed predominantly in brain and fetal heart. The ix3 cDNA detected two mRNA species: a ---4.5 kb mRNA present in most tissues and a ---6 kb mRNA, found only in fetal brain, adult brain, heart, and skeletal muscle. The deduced amino acid sequences of these isoforms are highly conserved. However, significant differences in codon usage and patterns of genomic DNA hybridization indicate that the a subunits are encoded by a multigene family. Structural analysis of the a subunits from rat and other species predicts a polytopic protein with seven membranespanning regions. Isoform diversity of the a subunit may provide a biochemical basis for Na,K-ATPase functional diversity.

Advances in Na+,K+‐ATPase studies: from protein to gene and back to protein

“…The largest amounts were found in kidney, the smallest in liver. Two or even three (r2 mRNAs (5.3-6, 3.4-4.5 and 2.4 kb) were found in different amounts in many rat tissues except for liver [61,62,64,65]. This variety could result from the differential use of the polyadenylation signals in the 3 '-untranslated region of cu2 mRNA [61].…”

Regulation of blastocyst formation

“…The enzyme establishes and maintains the high internal K + and low internal Na + concentrations found in eukaryotic cells (137)(138)(139)(140)(141)(142)(143)(144)(145)(146)(147)(148)(149). The enzyme actively transports 3 Na + out of the cell and 2 K + into the cell for each molecule of hydrolyzed ATP.…”

“…The beta-subunit of M r 40-60 kD facilitates the processing and insertion of the alpha-subunit into the plasma membrane (138,145). In mammals these subunits are encoded by multi-gene families consisting of four alpha subunit genes (alpha1, alpha2, alpha3, alpha 4) and three beta subunit genes (beta 1, beta 2, beta 3), each displaying a distinct temporal and spatial expression pattern (139)(140)(141)(142)(143)(144)(145)(146)(150)(151)(152). The gamma-subunit is a small (8-14 kD) hydrophobic peptide whose function is c urrently under investigation (146,148,150).…”

“…The Na + gradient provides the energy for Na + -coupled transporters that mediate the translocation of ions (H + , Ca 2+ , Cl -, PO 4 -), substrates (glucose and amino acids) and neurotransmitters (136). The catalytic alphasubunit of M r 100 kD is responsible for ion transport (139)(140)(141)(142)(143)(144)(145). The beta-subunit of M r 40-60 kD facilitates the processing and insertion of the alpha-subunit into the plasma membrane (138,145).…”

“…The enzyme actively transports 3 Na + out of the cell and 2 K + into the cell for each molecule of hydrolyzed ATP. The electrochemical gradient that the Na/K-ATPase generates is necessary for maintaining osmotic balance, the resting membrane potential, and the excitable properties of muscle and nerve cells (137)(138)(139)(140). The Na + gradient provides the energy for Na + -coupled transporters that mediate the translocation of ions (H + , Ca 2+ , Cl -, PO 4 -), substrates (glucose and amino acids) and neurotransmitters (136).…”