Cation antiports of animal plasma membranes.

Both organic and inorganic solutes can be transported across biological membranes against their electrochemical gradient, by coupling to the downhill movement of another species. In animal cells, the underlying mechanism most often involves symport (cotransport) or antiport (countertransport) with either sodium or hydrogen ions. The energy invested in the uphill translocation of solutes is ultimately provided by hydrolysis of ATP by Na+or H+-transporting ATPases and is transiently stored as potential energy in the form of an electrochemical gradient of these ions. This introductory review describes the properties of systems that catalyze both Na+or H+-driven countertransport of inorganic cations, present in vertebrates and invertebrates. Although great strides have been made towards the biochemical identification and characterization of vertebrate transporters, the molecular analysis of the invertebrate systems is still in its infancy. Only a brief comparative overview is provided for general reference in this introductory section. More specific descriptions of the individual systems and recent developments are described more fully in the following chapters. To shorten the reference list and to avoid redundancy with the following sections, comprehensive reviews were cited wherever possible and references to original work were kept to a minimum.