The Na+/K+ ATPasegenerates the Na+ and K+ concentration gradients across the plasma membrane and is thus essential for cellular electrolyte homeostasis, cell membrane potential and cell volume maintenance. A powerful regulator of Na+/K+ ATPase is the serum- and glucocorticoid-inducible kinase 1 (SGK1). The most powerful known regulator of SGK1 expression is TGF ss 1, which is pivotal in the regulation of megakaryocyte maturation and platelet formation. Signaling involved in the upregulation of SGK1 by TGF ss 1 includes p38 mitogen activated protein (MAP) kinase. SGK1 in turn phosphorylates the 1 kappa B kinase (IKK alpha/beta), which phosphorylates the inhibitor protein l kappa B alpha thus triggering nuclear translocation of nuclear factor kappa B (NF-kappa B). The present study explored whether TGF ss influences Na+/K+ ATPase activity in megakaryocytes, and if so, whether the effect of TG ss 1 requires p38 MAP kinase, SGK1 and/or NF-kappa B. To this end, murine megakaryocytes were treated with TGF ss 1 and ATPase activity determined from K+ induced current utilizing whole cell patch clamp. The pump current (I-pump) was determined in the absence and presence of Na+/K+ ATPase inhibitor ouabain (100 mu M). TGF ss 1 (60 ng/ml) was added in the absence or presence of p38 MAP kinase inhibitor skepinone-L (1 mu M), SGK1 inhibitor EMD638683 (50 mu M) or NF-kappa B inhibitor wogonin (50 nM). As a result, the I-pump was significantly increased by pretreatment of the megakaryocytes with TGF ss 1, an effect reaching statistical significance within 16 and 24 h and virtually abrogated in the presence of skepinone-L, EMD638683 or wogonin. In conclusion, TGF ss 1 is a powerful regulator of megakaryocytic ATPase activity. Signaling mediating the effect of TGF ss 1 on Na+/K+ ATPase activity involves p38 MAP kinase, SGK1 and NF-kappa B. (C) 2014 Elsevier Inc. All rights reserved.