Hypertension is the largest risk factor for cardiovascular disease, the leading cause of mortality worldwide. As blood pressure regulation is influenced by multiple physiological systems, hypertension cannot be attributed to a single identifiable etiology. Three decades of research into Mendelian forms of hypertension implicated alterations in the renal tubular sodium handling, particularly the distal convoluted tubule (DCT)-native, thiazide-sensitive Na-Cl cotransporter (NCC). Altered functions of the NCC have shown to have profound effects on blood pressure regulation as illustrated by the over activation and inactivation of the NCC in Gordon's and Gitelman syndromes respectively. Substantial progress has uncovered multiple factors that affect the expression and activity of the NCC. In particular, NCC activity is controlled by phosphorylation/dephosphorylation, and NCC expression is facilitated by glycosylation and negatively regulated by ubiquitination. Studies have even found parvalbumin to be an unexpected regulator of the NCC. In recent years, there have been considerable advances in our understanding of NCC control mechanisms, particularly

The solute carrier family 12(SLC12)of cation-chloride cotransporters(CCCs)comprises potassium chlo-ride cotransporters(KCCs,e.g.KCC1,KCC2,KCC3,and KCC4)-mediated Cl-extrusion,and sodium po-tassium chloride cotransporters(N[K]CCs,NKCC1,NKCC2,and NCC)-mediated Cl-loading.The CCCs play vital roles in cell volume regulation and ion homeostasis.Gain-of-function or loss-of-function of these ion transporters can cause diseases in many tissues.In recent years,there have been considerable ad-vances in our understanding of CCCs'control mechanisms in cell volume regulations,with many tech-niques developed in studying the functions and activities of CCCs.Classic approaches to directly measure CCC activity involve assays that measure the transport of potassium substitutes through the CCCs.These techniques include the ammonium pulse technique,radioactive or nonradioactive rubidium ion uptake-assay,and thallium ion-uptake assay.CCCs'activity can also be indirectly observed by measuring y-aminobutyric acid(GABA)activity with patch-clamp electrophysiology and intracellular chloride con-centration with sensitive microelectrodes,radiotracer 36Cl-,and fluorescent dyes.Other techniques include directly looking at kinase regulatory sites phosphorylation,flame photometry,22Na+uptake assay,structural biology,molecular modeling,and high-throughput drug screening.This review sum-marizes the role of CCCs in genetic disorders and cell volume regulation,current methods applied in studying CCCs biology,and compounds developed that directly or indirectly target the CCCs for disease treatments.