Kinetic characterization of α1 and α2/3Na+,K+-ATPase isoforms in cerebral cortex and hippocampus from rats

Kinetic properties of α 1 and α 2/3 isoforms of Na + , K + -ATPase (NKA) were evaluated in cerebral cortex (CX) and hippocampus (HP) homogenates of Wistar rats. In CX ATP curves, α 1 NKA (K 0.5 a = 0.04 ± 0.002 mM; V M a = 1.11 ± 0.02 U/mg; K 0.5 b= 2.56 ± 1.08 mM; V M b = 9.72 ± 3.56 U/mg) and α 2/3 NKA (K 0.5 a = 0.01 ± 0.001 mM; V M a = 1.17 ± 0.30 U/mg; K 0.5 b = 2.71 ± 1.87 mM; V M b = 1.88 ± 0.56 U/mg) isoforms showed biphasic curves. In HP, α 1 NKA showed K 0.5 a = 0.05 ± 0.03 mM; V M a = 2.77 ± 0.28 U/mg; K 0.5 b= 2.06 ± 0.60 mM; V M b = 4.91 ± 1.48 U/mg, while α 2/3 NKA showed monophasic curve (K 0.5 = 1.02 ± 0.01 mM; V M = 5.22 ± 1.88 U/mg). Under Na + stimulation, α 1 NKA in CX reached higher V M and affinity than α 2/3 NKA. Whereas HP V M was similar, but K 0.5 was higher in α 1 NKA. α 2/3 NKA exhibited higher affinity for K + and smaller V M than α 1 NKA in CX, but in HP both isoforms presented similar K 0.5 . In Mg 2+ assays, α 1 NKA showed higher affinities and activity in CX. In HP, the V M are similar across isoforms, but K 0.5 was higher in α 1 NKA than α 2/3 NKA. In increasing NH 4 + concentrations, α 1 NKA showed higher affinities than α 2/3 NKA in CX and HP, but α 2/3 NKA demonstrated higher V M . These results provide the first comparative kinetic characterization of α 1 and α 2/3 NKA isoforms in rat brain, highlighting regional and isoform-specific differences that may reflect distinct physiological demands.