Hyperosmolarity inhibits the Na+/H+ exchanger isoforms NHE2 and NHE3: an effect opposite to that on NHE1

The four Na+/H+ exchanger (NHE) isoforms have been shown to participate in the process of Na+ uptake by cells exposed to hypoosmotic media. Herein, PS120 cells transfected with cloned NHE1, NHE2 and NHE3 cDNAs were assessed for their responses when exposed to hyperosmolar solution. NHE activity of NHE2 and NHE3 was inhibited by hyperosmolarity. There was also a marked reduction in maximal reaction velocity, but no differences were observed in the Michaelis-Menten constant between the isoforms. Truncated forms of NHE3 cDNAs and NHE2 cDNA also inhibited NHE activity.