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. 1990 Nov;87(22):8990-4.
doi: 10.1073/pnas.87.22.8990.

Rabbit ileal villus cell brush border Na+/H+ exchange is regulated by Ca2+/calmodulin-dependent protein kinase II, a brush border membrane protein

M E Cohen  1 , L Reinlib, A J Watson, F Gorelick, K Rys-Sikora, M Tse, R P Rood, A J Czernik, G W Sharp, M Donowitz
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Rabbit ileal villus cell brush border Na+/H+ exchange is regulated by Ca2+/calmodulin-dependent protein kinase II, a brush border membrane protein

M E Cohen et al. Proc Natl Acad Sci U S A. 1990 Nov.

Abstract

Ileal brush border membranes contain an endogenous Ca2+/calmodulin (CaM)-dependent protein kinase activity that modulates the activity of the apical membrane Na+/H+ exchanger. To further characterize this kinase, synapsin I, a substrate for Ca2+/CaM-dependent protein kinases, was added to preparations of ileal brush border membranes. In the presence of Ca2+/CaM, synapsin I was phosphorylated. Phosphopeptide mapping demonstrated that the addition of Ca2+/CaM to brush border membranes stimulated the phosphorylation of sites in synapsin I specific for Ca2+/CaM-dependent protein kinase II. Immunoblots containing brush border and microvillus membrane proteins were probed with an antibody that recognizes the 50-kDa subunit of rat brain Ca2+/CaM-dependent protein kinase II. This antibody labeled major and minor species of 50 and 53 kDa, respectively, with more labeling of the brush border than the microvillus membranes. Right-side-out ileal villus cell brush border vesicles were prepared containing CaM, ATP, and 350 nM free Ca2+. Na+/H+ exchange was inhibited by the presence of Ca2+/CaM/ATP within the vesicles. A 21-amino acid peptide inhibitor of CaM kinase II was enclosed within some vesicle preparations by freeze-thaw. The effect on Na+/H+ exchange of Ca2+/CaM/ATP was partially reversed by the inhibitor peptide. These studies demonstrate the presence of Ca2+/CaM-dependent protein kinase II in rabbit ileal villus cell brush border membranes. Based on the effect of a specific inhibitor peptide of Ca2+/CaM kinase II, it is concluded that this kinase inhibits brush border Na+/H+ exchange, which participates in the regulation of ileal Na+ absorption.

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