It has been previously shown from our laboratory that abnormal functioning of Na/K ATPase can cause spreading depression, the likely mechanism of migraine aura. We used lymphocytes to investigate whether or not membrane Na/K ATPase is altered in migraine with aura patients. Lymphocytes were prepared from such patients, aged 20-45 years, and from age-matched healthy volunteers (controls). The binding of 3H- ouabain was studied using increasing concentrations (0.5-25 nm) of this radioligand, specific for Na/K-ATPase. We studied 19 migraine with aura patients and 22 healthy volunteers, matched for age and sex. B(max) (fmol/mg protein) and K(D) (nM) were not different between patients and controls. However, their ratio (B(max)/K(D)) was higher in patients than in controls. B(max) was (mean +/- SD) 270 +/- 110 fmol/mg protein in controls, and 360 +/- 230 in migraine with aura patients (P = 0.10, t-test). K(D) was (mean +/- SD) 2.8 +/- 1.5 nm in controls, and 2.9 +/- 3.2 nm in migraine with aura patients (P = 0.88, t-test). B(max)/K(D) was (mean +/- SD) 120 +/- 78 in controls, and 210 +/- 190 in migraine patients (P = 0.046, t-test). Moreover, no control patient had a B(max)/K(D) ratio greater than 398, while three migraine patients had ratios of 417, 572 and 722, respectively. Ouabain binding is affected by Na/K ATPase structure (K(D)) and expression (B(max)). While these parameters were not altered in migraine with aura patients, the difference in their ratio suggests an imbalance between the enzyme's ouabain affinity and its expression, with higher-affinity subtypes being more expressed than normal. Moreover, single patients had values quite different from the control population. Our data suggest that (i) ouabain binding to lymphocyte membranes may be a useful tool in the diagnosis of migraine with aura and (ii) Na/K ATPase abnormalities may be involved in migraine aura.