Regulation of the renal Na(+)-H+ exchanger by calcium calmodulin-dependent multifunctional protein kinase II

Prior studies indicate that cAMP-dependent protein kinase (PKA) and calcium calmodulin-dependent multifunctional protein kinase II (CaM-KII) inhibit Na(+)-H+ exchanger as assayed in octyl glucoside solubilized rabbit renal brush border membrane proteins reconstituted into artificial lipid vesicles. An anion exchange chromatography fraction of these proteins which elutes between 0.2 and 0.4 M NaCl (Fraction B), however, fails to demonstrate regulation of the transporter by PKA. The present studies examine regulation of the Na(+)-H+ exchanger by CaM-KII using Fraction B proteins. As compared to the initial total protein extract, Fraction B demonstrated increased Na(+)-H+ exchange activity. CaM-KII inhibited the Na(+)-H+ exchanger in Fraction B by 38.2 +/- 10.6% in an ATP and calmodulin-dependent manner. The results of the present studies suggest that CaM-KII-mediated inhibition of the Na(+)-H+ exchanger involves the phosphorylation of different polypeptides than those mediating the inhibition of this transporter by PKA.