Regulation of Na⁺pump expression by vascular smooth muscle cells

Abstract

The Na(+) pump and its regulation is important for maintaining membrane potential and transmembrane Na(+) gradient in all mammalian cells and thus is essential for cell survival and function. Vascular smooth muscle cells (VSMC) have a relatively low number of pump sites on their membrane compared with other cells. We wished to determine the mechanisms for regulating the number of pump sites in these cells. We used canine saphenous vein VSMC cultured in 10% serum and passaged one time. These cells were subcultured in 5% serum media with low K(+) (1 mM vs. control of 5 mM), and their pump expression was assessed. These VSMC upregulated their pump sites as early as 4 h after treatment (measured by [(3)H]ouabain binding). At this early time point, there was no detectable increase in protein expression of either alpha(1)- or beta(1)-subunits of the pump shown by Western blots. When the cells were treated with the phosphoinositide 3-kinase (PI-3-K) inhibitor LY-294002 (which is known to inhibit cytoplasmic transport processes) in low-K(+) media, the pump site upregulation was inhibited. These data suggest that the low-K(+)-induced upregulation of Na(+) pump number can occur by translocation of preformed pumps from intracellular stores.

Inhibition of Na,K-ATPase Activates PI3 Kinase and Inhibits Apoptosis in LLC-PK1 Cells

“…Partial inhibition of Na,K-ATPase also increases the activity of the pump. Compatible with the present observation, Aydemir-Koksoy and Allen have recently demonstrated that LY 294002 inhibits the upregulation of Na,KATPase binding sites by low K ϩ in vascular smooth muscle cells (14). The mechanism by which Na,K-ATPase inhibition leads to PI3 kinase activation is not clear at present time.…”

Ouabain-induced Signaling and Vascular Smooth Muscle Cell Proliferation

“…The increase in DNA synthesis and proliferation effects disappeared with increased ouabain concentrations, but a small increment in MAPK activation remained. Considering the limited number of pump sites and expression of only one isoform of the sodium pump in these cells (15), this finding suggests that at higher concentrations the pump-inhibitory effect of ouabain might interfere with its proliferative effect. The concentrations at which we observed a significant increase in BrdUrd uptake, proliferation, and MAPK42/44 activation are ϳ100 times lower than the K d for ouabain for these cells (…”

Antiproliferative Activity of Derivatives of Ouabain, Digoxin and Proscillaridin A in Human MCF-7 and MDA-MB-231 Breast Cancer Cells

“…39) However, the cell death-promoting activity of cardiac glycosides appears cell type specific, because other work has shown that they inhibit multiple pathways of apoptosis in vascular smooth muscle cells. 1,40) The signalling pathways that are rapidly activated by the interaction of cardiac glycosides and their derivatives with the sodium pump and which are independent of changes in intra-cellular Na ϩ and K ϩ concentrations, include activation of Src kinase, transactivation of the epidermal growth factor receptor (EGFR) by Src, modulation of the NF-kB activity, activation of Ras and P42/P44 mitogen-activated protein kinases and increased generation of reactive oxygen species by mitochondria. Several cardiac glycosides provoke an increase in [Ca 2ϩ ] i as the result of the activation of these downstream signalling pathways.…”