sentences:  Comparison of their sequences with those of other ion-transporting membrane proteins reveals that they are part of a new superfamily of cation-chloride co-transporters, which includes the Na-Cl and Na-K-2Cl co-transporters.KCC1 and KCC3 are widely expressed in human tissues, while KCC2 is expressed only in brain neurones, making it likely that this is the isoform responsible for maintaining low Cl− concentration in neurones.KCC1 is widely expressed in human tissues, and when heterologously expressed, possesses the functional characteristics of the well-studied red blood cell K-Cl co-transporter, including stimulation by both swelling and N-ethylmaleimide.