Heterogeneous Na + Sensitivity of Na + ,K + -ATPase Isoenzymes in Whole Brain Membranes (original) (raw)

1993, Journal of Neurochemistry

The >.laf sensitivity of whole brain membrane Na+,K+-ATPase isoenzymes was studied using the differential inhibitory effect of ouabain ( a I , low affinity for ouabain; a2, high affinity; and 013, very high affinity). At 100 mM Na+, we found that the proportion of isoforms with low, high, and very high ouabain affinity was 21, 38, and 4 1 %, respectively. Using two ouabain concentrations (lo-' and lo-' M ) , we were able to discriminate Na+ sensitivity of Na+, K+-ATPase isoenzymes using nonlinear regression. The ouabain lowaffinity isoform, a 1, exhibited high Na+ sensitivity [K, of3.88 f 0.25 mMNa+ and a Hill coefficient (n) of I .98 t 0.131; the ouabain high-affinity isoform, a2, had two Na+ sensitivities, a high (K, of 4.98 k 0.2 M N a + andnof 1.34t-0.10)andalow(K,of28-+0.5mMNa+and an n of 1.92 t-0.18) Na+ sensitivity activated above a threshold (22 * 0.3 mMNa+); and the ouabain very-high-affinity isoform, a3, was resolved by two processes and appears to have two Na' sensitivities (apparent K, values of 3.5 and 20 m M Naf). We show that Na+ dependence in the absence of ouabain is the result of at least of five Na' reactivities. This molecular functional characteristic of isoenzymes in membranes could explain the diversity of physiological roles attributed to isoenzymes. Key Words: Na+,K+-ATPase-Mathematical analysis-Na+ sensitivity-Ouabain-Isoenzyme-Whole brain (rat). Gerbi A. et al. Heterogeneous Na+ sensitivity of Na+,K+-ATPase isoenzymes in whole brain membranes. J. Nrurochem. 60,[246][247][248][249][250][251][252].