Background A circulating inhibitor of the sodium, potassium adenosine triphosphatase (Na+, K+ ATPase) enzyme has been described in allergic subjects. Recent studies have suggested that the Na+, K+ ATPase enzyme may be involved in the signal transduction pathways of various cell types and that inhibition of its activity can modulate histamine release from basophils and mast cells.
Objective The purpose of this study was to determine if modulation of Na+, K+ ATPase activity alters degranulation in the 2H3 subline of rat basophitic leukaemia cells (RBL-2H3), a mucosal mast cell model bearing high-affinity Fc receptors for IgE.
Methods Degranulation was measured by the release of both exogenous serotonin and endogenous histamine. Na+, K+ ATPase activity was assessed by ouabain-sensitive [86rubidium] uptake ([86Rb] uptake) and ex situ enzyme activity.
Results Ouabain-sensitive [86Rb] uptake and degranulation increased in parallel and in a dose–response fashion with increasing Fc receptor cross-linking. Additionally, incubation with ouabain, a known inhibitor of Na+, K+ ATPase activity, decreased both anti-IgE and calcium ionophore-induced degranulation, but increased spontaneous degranulation, each in a dose-response manner. Moreover, the effect of ouabain on degranulation was reversed by rinsing and mimicked by other known inhibitors of Na+, K+ ATPase activity. Finally, in the absence of anti-IgE or calcium ionophore, stimulation of ouabain-sensitive [86Rb] uptake by the sodium (Na+) ionophore monensin was associated with a corresponding dose–response increase in ouabain-sensitive degranulation. These experiments demonstrate that ouabain-sensitive [86Rb] uptake increases following IgE receptor cross-linking in RBL-2H3, and that factors which modulate Na+, K+ ATPase activity in these cells may also regulate degranulation.
Conclusion The results of this study suggest an important role for Na+, K+ ATPase activation in the signal transduction pathway of stimulated RBL-2H3.