Background: There are numerous reports of abnormalities in the expression of the sodium- and potassium-activated adenosine triphosphatase (Na,K-ATPase) in response to an ionic stress with ethacrynic acid (ECA) challenge in bipolar subjects. However, all of these studies have been in out-bred populations. In an attempt to reduce the genetic variability associated with this observation, we examined this phenomenon within an isolated breeding population.
Methods: We studied 36 lymphoblastoid cell lines obtained from Old Order Amish individuals who had bipolar disorder, type I (16), or were unaffected siblings of the same gender (9) or unrelated normal controls(11). Cells were treated with 10(-)(5)M ECA for 3 days after which Na,K-ATPase alpha1 protein expression and activity ([(3)H]-ouabain binding, (86)Rb-uptake, and intracellular sodium and potassium concentrations) were measured.
Results: Cells from bipolar patients expressed less Na,K-ATPase as measured by immunoblot analysis after ECA treatment (0.94 + or - SD 0.13 relative units) compared to unaffected siblings (1.06 + or - 0.12, P = 0.029) and Old Order Amish normal controls (1.06 + or - 0.14, P = 0.0004). None of the other variables studied were different.
Limitations: This is a study of peripheral cells which do not express all of the Na,K-ATPase expressed in the brain. The observed difference is small.
Conclusions: Ethacrynic-acid-stimulated lymphoblast sodium pump expression in Old Order Amish bipolar subjects is reduced compared to Amish controls.
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