RESUMO
Previous investigations have documented a reduced activity of the sodium-potassium-stimulated adenosine triphosphatase enzyme (Na+,K+ ATPase) in platelet membranes of allergic subjects. The purpose of this study was to determine if the reduced Na+,K+ ATPase activity was due to an enzyme inhibitor. Na+,K+ ATPase activity of a particulate fraction of sonicated platelets was determined by spectrophotometry in asymptomatic adults with and without allergy. The Na+,K+ ATPase level (mean, nanomoles per microgram of protein per minute; +/- STD) of allergic subjects (0.9 +/- 1.3) was lower (p less than 0.001) than that of nonallergic subjects (3.9 +/- 1.6). In contrast, when the same platelet fractions were frozen before assay, Na+,K+ ATPase was higher (p less than 0.005) in allergic subjects (6.0 +/- 1.4) than in nonallergic subjects (3.6 +/- 2.0). An inhibitor of canine kidney Na+,K+ ATPase was detected in the buffer in which these platelet fractions were frozen, allergic subjects (0.5% +/- 0.4% inhibition per microgram of protein) compared to nonallergic subjects (0.04% +/- 0.08%; p less than 0.005). The level of inhibition correlated positively with the postfreezing increase in platelet membrane Na+,K+ ATPase, suggesting a freezing-induced displacement of an inhibitor from the membrane. Plasma from these same subjects inhibited Na+,K+ ATPase activity of normal platelets, allergic subjects (70% +/- 31% inhibition) compared to nonallergic subjects (13% +/- 16%; p less than 0.001). These data suggest that the transport-enzyme defect observed in platelets from allergic subjects was due to a circulating Na+,K+ ATPase inhibitor. In vivo Na+,K+ ATPase inhibition in allergy could have profound effects on intracellular cation concentrations and broad implications for pathogenesis.
Assuntos
Asma/sangue , Plaquetas/enzimologia , Rinite Alérgica Perene/sangue , Rinite Alérgica Sazonal/sangue , ATPase Trocadora de Sódio-Potássio/antagonistas & inibidores , Adulto , Asma/etiologia , Membrana Celular/enzimologia , Congelamento , Humanos , Rinite Alérgica Perene/etiologia , Rinite Alérgica Sazonal/etiologia , ATPase Trocadora de Sódio-Potássio/sangueRESUMO
A pathogenic role and abnormal function have both been ascribed to the blood platelet in allergy, but the explanation for these observations is unknown. This study compared the cation-stimulated adenosine triphosphatase enzyme (ATPase) activities of platelets from allergic (n = 18), potentially allergic (asymptomatic, positive skin test, n = 5) and normal patients (n = 10), all of whom were without symptoms at the time of the study. Platelets were separated by centrifugation, were sonicated, and were assayed for cation-dependent ATPase activity by spectrophotometry. The mean Na+,K(+)-ATPase activity (in nanomoles per microgram protein per minute) of allergic subjects (0.94 +/- 1.28) was significantly lower than that of normal subjects (3.93 +/- 1.58). No Na+,K(+)-ATPase activity was detectable in platelets from eight of the allergic subjects. The Na+,K(+)-ATPase activity of potentially allergic subjects was intermediate between those of the allergic and normal subjects. A significant negative correlation (p less than 0.01) was observed between serum IgE levels and platelet Na+,K(+)-ATPase values, thus suggesting a relationship between the reduced platelet Na+,K(+)-ATPase and IgE immunoglobulin. No such differences were observed for the Ca+(+)- and Mg+(+)-stimulated ATPases. In vivo dysfunction of the plasma membrane Na+,K(+)-ATPase enzyme in allergic subjects could have profound effects on levels of intracellular cations and thus platelet activation and function.