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Heterogeneous Na + Sensitivity of Na + ,K + ‐ATPase Isoenzymes in Whole Brain Membranes
Author(s) -
Gerbi Alain,
Debray Marcel,
Maixent JeanMichel,
Chanez Claude,
Bourre JeanMarie
Publication year - 1993
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1993.tb05844.x
Subject(s) - ouabain , isozyme , chemistry , membrane , gene isoform , ligand (biochemistry) , alpha (finance) , sodium , enzyme , biochemistry , receptor , medicine , construct validity , nursing , organic chemistry , patient satisfaction , gene
The Na + sensitivity of whole brain membrane Na + ,K + ‐ATPase isoenzymes was studied using the differential inhibitory effect of ouabain (α1, low affinity for ouabain; α2, high affinity; and α3, very high affinity). At 100 m M Na + , we found that the proportion of isoforms with low, high, and very high ouabain affinity was 21, 38, and 41%, respectively. Using two ouabain concentrations (10 −5 and 10 −7 M ), we were able to discriminate Na + sensitivity of Na + , K + ‐ATPase isoenzymes using nonlinear regression. The ouabain low‐affinity isoform, α1, exhibited high Na + sensitivity [ K a of 3.88 ± 0.25 m M Na + and a Hill coefficient ( n ) of 1.98 ± 0.13]; the ouabain high‐affinity isoform, α2, had two Na + sensitivities, a high ( K a of 4.98 ± 0.2 m M Na + and n of 1.34 ± 0.10) and a low ( K a of 28 ± 0.5 m M Na + and an n of 1.92 ± 0.18) Na + sensitivity activated above a thresh old (22 ± 0.3 m M Na + ); and the ouabain very‐high‐affinity isoform, α3, was resolved by two processes and appears to have two Na + sensitivities (apparent K a values of 3.5 and 20 m M Na + ). 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.