Volume regulation by most vertebrate cells is due to K loss following swelling and Na uptake subsequent to shrinkage. Insights into volume-dependent coordination of K loss and Na uptake were obtained by Jennings (Jennings et al., 1990) employing a two state model to assess the relative magnitudes of the forward and reverse reactions controlling transport. In systems thus analyzed, swelling-induced KCl cotransport and shrinkage-induced Na/H exchange are activated by dephosphorylation and phosphorylation respectively, where only the kinase is volume-sensitive. In contrast, K/H exchange mediated K loss and Na/H exchange dependent Na uptake by Amphiuma red cells are stimulated by phorbol ester and calyculin A, suggesting that activation of both pathways is kinase dependent. Following Jennings lead and analyzing the relaxation kinetics of Amphiuma Na/H and K/H exchangers we conclude that swelling stimulates the kinase activating K/H exchange and inhibits the opposing phosphatase. Similarly, shrinkage stimulates the kinase activating Na/H exchange and inhibits the opposing phosphatase. Volume-dependent coordination is achieved since kinase activity controlling the active pathway (Na/H or K/H exchange) is large while the opposing phosphatase is small yet the kinase which controls activity of the inactive pathway is small while activity of its opposing phosphatase is large.
|Original language||English (US)|
|State||Published - Mar 20 1998|
ASJC Scopus subject areas
- Agricultural and Biological Sciences (miscellaneous)
- Biochemistry, Genetics and Molecular Biology(all)
- Cell Biology