Novel bUT-B2 urea transporter isoform is constitutively activated

2009 ◽  
Vol 297 (2) ◽  
pp. R323-R329 ◽  
Author(s):  
P. Tickle ◽  
A. Thistlethwaite ◽  
C. P. Smith ◽  
G. S. Stewart

Our previous studies have detailed a novel facilitative UT-B urea transporter isoform, bUT-B2. Despite the existence of mouse and human orthologs, the functional characteristics of UT-B2 remain undefined. In this report, we produced a stable MDCK cell line that expressed bUT-B2 protein and investigated the transepithelial urea flux across cultured cell monolayers. We observed a large basal urea flux that was significantly reduced by known inhibitors of facilitative urea transporters; 1,3 dimethylurea ( P < 0.001, n = 17), thionicotinamide ( P < 0.05, n = 11), and phloretin ( P < 0.05, n = 9). Pre-exposure for 1 h to the antidiuretic hormone vasopressin had no effect on bUT-B2-mediated urea transport (NS, n = 3). Acute vasopressin exposure for up to 30 min also failed to elicit any transient response (NS, n = 9). Further investigation confirmed that bUT-B2 function was not affected by alteration of intracellular cAMP (NS, n = 4), intracellular calcium (NS, n = 3), or protein kinase activity (NS, n = 4). Finally, immunoblot data suggested a possible role for glycosylation in regulating bUT-B2 function. In conclusion, this study showed that bUT-B2-mediated transepithelial urea transport was constitutively activated and unaffected by known regulators of renal UT-A urea transporters.

1976 ◽  
Vol 35 (03) ◽  
pp. 635-642 ◽  
Author(s):  
M Steiner

SummaryThe effect of thrombin on the phosphorylating activity of platelet membranes was compared to that of trypsin. Preincubation of non-32P phosphorylated platelet membranes with or without either of these two enzymes resulted in a considerable loss of membrane protein kinase activity which was most severe when trypsin was used. Protein kinase activity and endogenous protein acceptors decreased in parallel. 32P-phosphorylated membranes showed a slow but progressive loss of label which was accelerated by trypsin. Thrombin under these conditions prevented the loss of 32P-phosphate. These results are interpreted to indicate a thrombin-induced destruction of a phosphoprotein phosphatase. The protein kinase activity of phosphorylated platelet membranes using endogenous or exogenous protein substrates showed a significant reduction compared to non-phosphorylated membranes suggesting a deactivation of protein kinase by phosphorylation of platelet membranes. Neither thrombin nor trypsin caused a qualitative change in the membrane polypeptides accepting 32P-phosphate but resulted in quantitative alterations of their ability to become phosphorylated.


1989 ◽  
Vol 264 (24) ◽  
pp. 14549-14555 ◽  
Author(s):  
D Kübler ◽  
W Pyerin ◽  
O Bill ◽  
A Hotz ◽  
J Sonka ◽  
...  

1996 ◽  
Vol 191 (2) ◽  
pp. 281-282 ◽  
Author(s):  
J. Kanungo ◽  
B. Calhoun ◽  
Y. Takeda ◽  
J. A. Hardin ◽  
H. Rasmussen

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