Phorbol 12-myristate 13-acetate down-regulates Na,K-ATPase independent of its protein kinase C site: decrease in basolateral cell surface area.

Abstract

The effect of protein kinase C (PKC) stimulation on the pump current (Up) generated by the Na,K-ATPase was measured in A6 epithelia apically permeabilized with amphotericin B. Phorbol 12-myristate 13-acetate (PMA) produced a decrease in I carried by sodium pumps containing the endogenous Xenopus laevis or transfected BuJ'o marinus al subunits (-30% reduction within 25 min, maximum after 40 min) independent of the PKC phosphorylation site (T15A/S16A). In addition to this major effect of PMA, which was independent of the intracellular sodium concentration and was prevented by the PKC inhibitor bisindolylmaleimide GF 109203X (BIM), another BIM-resistant, PKC siteindependent decrease was observed when the Ip was measured at low sodium concentrations (total reduction -50% at 5 mM sodium). Using ouabain binding and cell surface biotinylation, stimulation of PKC was shown to reduce surface Na,K-ATPase by 14 to 20% within 25 min. The same treatment stimulated fluid phase endocytosis sevenfold and decreased by 16.5% the basolateral cell surface area measured by transepithelial capacitance measurements. In conclusion, PKC stimulation produces a decrease in sodium pump function which can be attributed, to a large extent, to a withdrawal of sodium pumps from the basolateral cell surface independent of their PKC site. This

Adenosine inhibits the transfected Na+‐H+ exchanger NHE3 in Xenopus laevis renal epithelial cells (A6/C1)

“…Somewhat unexpected is the type of control of basolateral XNHE activity, since PKC has been reported to upregulate the activity of XL-NHE, which as stated above is highly homologous to XNHE. Although direct proof is as yet not available, a decrease in basolateral membrane area, as recently observed in A6 cells in response to PKC stimulation (Beron et al 1997), could explain the overall inhibitory effect of PMA on basolateral XNHE activity. Alternatively, kidney-specific splicing of the amphibian Na¤-H¤ exchanger may be responsible for the ability of the exchanger to positively or negatively respond to PKC stimulation.…”

Subcellular Redistribution Is Involved in Acute Regulation of the Brush Border Na+/H+ Exchanger Isoform 3 in Human Colon Adenocarcinoma Cell Line Caco-2

“…Thus, our working hypothesis is that PKC inhibits NHE3 in Caco-2 cells by both stimulating translocation of the exchanger molecules from BB into SAC as well and changing the turnover number of the residual BB molecules. Simultaneous occurrence of both mechanisms has been suggested for multiple plasma membrane transport proteins including retinal taurine transporter (43), glucose transporters GLUT1 and GLUT4 (44), and Na ϩ ,K ϩ -ATPase (24,27). It will be important to further define the relative contribution of each of these two mechanisms in the acute regulation of NHE3 in both epithelial and nonepithelial cells.…”

“…Well characterized examples include glucose transporters GLUT1 and GLUT4 in adipocytes (19), the K ϩ ,H ϩ -ATPase pump in gastric parietal cells (20), the water channel aquaporin 2 in the kidney (21), the renal NaPi-2 cotransporter (22), the Na ϩ /glucose cotransporter SGLT1 (23), the renal Na ϩ ,K ϩ -ATPase pump (24), and the cystic fibrosis transmembrane conductance regulator (CFTR) (25). Much less is known, however, about the mechanisms of short term regu-lation of NHE3.…”

Molecular basis for the inhibition of G protein-coupled inward rectifier K+channels by protein kinase C

“…Other studies suggest that GIRK channel inhibition by certain excitatory neurotransmitters may be mediated by PIP 2 depletion (19,21,27,28). In addition, PMA may affect endocytosis changing GIRK channel activity through GIRK protein turnover (53,54).…”