Mechanism of ADH-induced enhancement of active ammonium absorption by the mouse medullary thick ascending limb

Regulation of NKCC2 splicing and phosphorylation

PURPOSE OF REVIEW

Transepithelial salt transport in the thick ascending limb of Henle's loop (TAL) crucially depends on the activity of the Na/K/2Cl cotransporter NKCC2. The pharmacologic blockade of NKCC2 leads to pronounced natriuresis and diuresis, which indicate key roles for NKCC2 in renal salt retrieval. The inadequate regulation of NKCC2 and the loss of NKCC2 function are associated with the disruption of salt and water homoeostasis. This review provides a specific overview of our current knowledge with respect to the regulation of NKCC2 by differential splicing and phosphorylation.

RECENT FINDINGS

Several mechanisms have evolved to adapt NKCC2 transport to reabsorptive needs. These mechanisms include the regulation of NKCC2 gene expression, the differential splicing of the NKCC2 pre-mRNA, the membrane trafficking, and the modulation of the specific transport activity. Substantial progress has been made over the past few years in deciphering the function of kinases in the regulatory network controlling NKCC2 activity and in elucidating the underlying mechanism and the functional consequences of the regulated differential splicing of the NKCC2 pre-mRNA.

SUMMARY

NKCC2 differential splicing and phosphorylation are critically involved in the modulation of the thick ascending limb of Henle's loop reabsorptive capacity and, consequently, in salt homoeostasis, volume regulation, and blood pressure control.

Physiology and pathophysiology of the renal Na-K-2Cl cotransporter (NKCC2)

The Na-K-2Cl cotransporter (NKCC2; BSC1) is located in the apical membrane of the epithelial cells of the thick ascending limb of the loop of Henle (TAL). NKCC2 facilitates ∼20–25% of the reuptake of the total filtered NaCl load. NKCC2 is therefore one of the transport proteins with the highest overall reabsorptive capacity in the kidney. Consequently, even subtle changes in NKCC2 transport activity considerably alter the renal reabsorptive capacity for NaCl and eventually lead to perturbations of the salt and water homoeostasis. In addition to facilitating the bulk reabsorption of NaCl in the TAL, NKCC2 transport activity in the macula densa cells of the TAL constitutes the initial step of the tubular-vascular communication within the juxtaglomerular apparatus (JGA); this communications allows the TAL to modulate the preglomerular resistance of the afferent arteriole and the renin secretion from the granular cells of the JGA. This review provides an overview of our current knowledge with respect to the general functions of NKCC2, the modulation of its transport activity by different regulatory mechanisms, and new developments in the pathophysiology of NKCC2-dependent renal NaCl transport.