The NH2-terminus of K+-Cl− cotransporter 3a is essential for up-regulation of Na+,K+-ATPase activity

K+-Cl− cotransporter-3 has two major amino terminal variants, KCC3a and KCC3b. In LLC-PK1 cells, exogenously expressed KCC3a co-immunoprecipitated with endogenous Na+,K+-ATPase α1-subunit (α1NaK), accompanying significant increases of the Na+,K+-ATPase activity. Exogenously expressed KCC3b did not co-immunoprecipitate with endogenous α1NaK inducing no change of the Na+,K+-ATPase activity. A KCC inhibitor attenuated the Na+,K+-ATPase activity in rat gastric mucosa in which KCC3a is predominantly expressed, while it had no effects on the Na+,K+-ATPase activity in rat kidney in which KCC3b is predominantly expressed. In these tissue samples, KCC3a co-immunoprecipitated with α1NaK, while KCC3b did not. Our results suggest that the NH2-terminus of KCC3a is a key region for association with α1NaK, and that KCC3a but not KCC3b can regulate the Na+,K+-ATPase activity.

Research highlights
► KCC3a but not KCC3b up-regulates the Na+,K+-ATPase activity in LLC-PK1 cells.
► KCC3a but not KCC3b is associated with Na+,K+-ATPase in isolated rat tissues.
► NH2-terminus of KCC3a is essential for association with Na+,K+-ATPase.