Vasopressin-induced stimulation of the Na+-activated K+ channels is responsible for maintaining the basolateral K+ conductance of the thick ascending limb (TAL) in EAST/SeSAME syndrome

Abstract

The renal phenotype of EAST syndrome, a disease caused by the loss-of-function-mutations of Kcnj10 (Kir4.1), is a reminiscence of Gitelman's syndrome characterized by the defective function in the distal convoluted tubule (DCT). The aim of the present study is to test whether antidiuretic hormone (vasopressin)-induced stimulation of the Na+-activated 80-150 pS K+ channel is responsible for compensating the lost function of Kcnj10 in the thick ascending limb (TAL) of subjects with EAST syndrome. Immunostaining and Western blot showed that the expression of aquaporin 2 (AQP2) was significantly higher in Kcnj10-/- mice than those of WT littermates, suggesting that the disruption of Kcnj10 stimulates vasopressin response in the kidney. The role of vasopressin in stimulating the basolateral K+ conductance of the TAL was strongly indicated by the finding that the application of arginine-vasopressin (AVP) hyperpolarized the membrane in the TAL of Kcnj10-/- mice. Application of AVP significantly stimulated the 80-150 pS K+ channel in the TAL and this effect was blocked by tolvaptan (V2 receptor antagonist) or by inhibiting PKA. Moreover, the water restriction for 24 hours significantly increased the probability of finding the 80-150 pS K+ channel and the K+ channel open probability in the TAL. The application of a membrane permeable cAMP analog also mimicked the effect of AVP and activated this K+ channel, suggesting that cAMP-PKA pathway stimulates the 80-150 pS K+ channels. The role of the basolateral K+ conductance in maintaining transcellular Cl- transport is further suggested by the finding that the inhibition of basolateral K+ channels significantly diminished the AVP-induced stimulation of the basolateral 10 pS Cl- channels. We conclude that vasopressin stimulates the 80-150 pS K+ channel in the TAL via a cAMP-dependent mechanism. The vasopressin-induced stimulation of K+ channels is responsible for compensating lost function of Kcnj10 thereby rescuing the basolateral K+ conductance which is essential for the transport function in the TAL.

Discovery, Characterization, and Effects on Renal Fluid and Electrolyte Excretion of the Kir4.1 Potassium Channel Pore Blocker, VU0134992

“…Genetic ablation of KCNJ10 has no effect on the basolateral V m in the TAL due to compensatory upregulation of the 80-pS channel (Zhang et al, 2015), suggesting that depolarization of the basolateral V m in the TAL is unlikely to contribute to salt wasting in KCNJ10 knockout mice and patients with EAST/SeSAME syndrome (Bockenhauer et al, 2009;Scholl et al, 2009). Interestingly, however, the inhibition of the 40-pS channel with Ba 21 reduces the activity of basolateral ClC-Kb Cl 2 channels through mechanisms that are currently unclear but do not appear to involve membrane depolarization (Fan et al, 2015). These data suggest that the natriuretic and diuretic effects of VU0134992 could result, at least in part, in the inhibition of NaCl reabsorption in the TAL, as follows.…”

“…The basolateral K 1 conductance of the cortical TAL is carried by a 40-pS channel that is likely composed of Kir4.1-5.1 heteromeric channels, and an 80-pS channel possibly carried by Na 1 -activated K 1 channels (Fan et al, 2015;Zhang et al, 2015) (Fig. 6).…”

Basolateral Kir4.1 activity in the distal convoluted tubule regulates K secretion by determining NaCl cotransporter activity

“…The possibility that Kir4.1 function in the cTAL could be compensated is also supported by patch-clamp experiments performed in p9 neonatal Kcnj10 −/− mice demonstrating that the disruption of Kir4.1 stimulates the activity of Na + and Cl − -activated 80- to 150-pS K + channel (K ca 4.1 or slo 2.2) in the cTAL [27;28]. The upregulation of Na-activated 80–150 pS K channel in the TAL may be induced by high vasopressin level in p9 neonatal Kir4.1 knockout mice as evidenced by the finding that AQP2 expression was upregulated [29]. …”

“…Moreover, we reasoned that a high vasopressin level may be mainly responsible for the stimulation of ENaC-β and γ expression in p9 neonatal Kcnj10 −/− mice because vasopressin has been shown to stimulate the expression of ENaC-β subunit [63]. Furthermore, our previous studies showed that the disruption of Kir4.1 increased AQP2 expression, suggesting Kcnj10 −/− mice have a high vasopressin level [29]. …”

The importance of the thick ascending limb of Henle’s loop in renal physiology and pathophysiology

“…Fan et al demonstrated that the vasopressin-dependent stimulation of the 80-150 pS basolateral K + channel in Kcnj10 (Kir 4.1) KO mice counteracts the loss of function of Kir 4.1 in the TAL, preventing defective salt absorption at this nephron site. 86 …”