Abstract
This review focuses on the mechanisms whereby the cytosolic Ca2+ regulates the ubiquitous Na+/ H+ exchanger (NHE-1) and how these regulatory processes might modify the behavior of NHE-1 in essential hypertension. The pH setpoint for activation of the Na+/H+ exchanger is controlled by two interrelated and Ca(2+)-dependent pathways, namely, the protein kinase/ phosphatase cascade and Ca2+/calmodulin. The cytoplasmic domain of NHE-1 contains elements responsive to serine/theorine kinases and a high affinity binding site to Ca2+/calmodulin. Phosphorylation of NHE-1 or the binding of the Ca2+/calmodulin complex to its binding site promotes an alkaline shift in the pH setpoint for the exchanger. It is suggested that, in essential hypertension, an increased cellular Ca2+ load or an enhanced external Ca2+ entry stimulate the NHE-1 through protein kinase/phosphatase and Ca2+/calmodulin systems, thereby increasing its activity.