Regulatory mechanism of "K+recycling" for Na +reabsorption in renal tubules

EAST/SeSAME syndrome: Review of the literature and introduction of four new Latvian patients

EAST (Epilepsy, Ataxia, Sensorineural deafness, Tubulopathy) or SeSAME (Seizures, Sensorineural deafness, Ataxia, Mental retardation, and Electrolyte imbalance) syndrome is a rare autosomal recessive syndrome first described in 2009 independently by Bockenhauer and Scholl. It is caused by mutations in KCNJ10, which encodes Kir4.1, an inwardly rectifying K⁺ channel found in the brain, inner ear, kidney and eye. To date, 16 mutations and at least 28 patients have been reported. In this paper, we review mutations causing EAST/SeSAME syndrome, clinical manifestations in detail, and efficacy of treatment in previously reported patients. We also report a new Latvian kindred with 4 patients. In contrast to the majority of previous reports, we found a progressive course of the disorder in terms of hearing impairment and neurologic deficit. The treatment is based on antiepileptic drugs, electrolyte replacement, hearing aids and mobility devices. Future research should concentrate on recognizing the lesions in the central nervous system to evaluate new potential diagnostic criteria and on formally evaluating intellectual disability.

Tanshinone IIA protects against pulmonary arterial hypertension in broilers

This investigation was conducted to study the effects of tanshinone IIA (TIIA) on pulmonary arterial hypertension (PAH) in broilers. Two-hundred newly hatched Arbor Acre commercial broilers were randomly divided into 3 groups. All groups, with the exception of the control group (tap water), were given NaCl water (0.3%) starting on the d 15, and broilers in the protected group were fed a diet supplemented with TIIA (2.5 g/kg) starting on the d 15. On d 28, 35, 42, and 49, the ratio of the right ventricular weight to the total ventricular weight (RV: TV) and the values of other biochemical indicators for each group chickens were determined. The concentrations of interleukin-6 (IL-6), interleukin-1β (IL-1β), nuclear factor kappa (NF-κB), and P38 (a mitogen-activated protein kinase) were measured using enzyme-linked immune sorbent assays (ELISA). The results showed that the proportion of chickens in the diseased group with an RV:TV ratio in the range of 0.250 to 0.299 (10%) was significantly higher (25 to 30%) compared to that of the other groups (P < 0.05), and the proportion in all chickens was 28%. In addition, the IL-6, IL-1β, NF-κB, and P38 protein concentrations were higher in the diseased group, whereas there were no differences between the control group and the protected group. Moreover, the measurements of body weight, liver function, kidney function and electrolytes showed significant differences between the diseased group and the other groups. These findings suggest that tanshinone IIA may protect broilers from PAH, which is an important piece of information for the poultry industry.

Role and mechanisms of regulation of the basolateral Kir 4.1/Kir 5.1K+ channels in the distal tubules

Epithelial K+ channels are essential for maintaining electrolyte and fluid homeostasis in the kidney. It is recognized that basolateral inward-rectifying K+ (Kir ) channels play an important role in the control of resting membrane potential and transepithelial voltage, thereby modulating water and electrolyte transport in the distal part of nephron and collecting duct. Monomeric Kir 4.1 (encoded by Kcnj10 gene) and heteromeric Kir 4.1/Kir 5.1 (Kir 4.1 together with Kir 5.1 (Kcnj16)) channels are abundantly expressed at the basolateral membranes of the distal convoluted tubule and the cortical collecting duct cells. Loss-of-function mutations in KCNJ10 cause EAST/SeSAME tubulopathy in humans associated with salt wasting, hypomagnesaemia, metabolic alkalosis and hypokalaemia. In contrast, mice lacking Kir 5.1 have severe renal phenotype that, apart from hypokalaemia, is the opposite of the phenotype seen in EAST/SeSAME syndrome. Experimental advances using genetic animal models provided critical insights into the physiological role of these channels in electrolyte homeostasis and the control of kidney function. Here, we discuss current knowledge about K+ channels at the basolateral membrane of the distal tubules with specific focus on the homomeric Kir 4.1 and heteromeric Kir 4.1/Kir 5.1 channels. Recently identified molecular mechanisms regulating expression and activity of these channels, such as cell acidification, dopamine, insulin and insulin-like growth factor-1, Src family protein tyrosine kinases, as well as the role of these channels in NCC-mediated transport in the distal convoluted tubules, are also described.

Mislocalization of K+ channels causes the renal salt wasting in EAST/SeSAME syndrome

The Kir4.1/Kir5.1 channel mediates basolateral K(+) recycling in renal distal tubules; this process is critical for Na(+) reabsorption at the tubules. Mutations in Kir4.1 are associated with EAST/SeSAME syndrome, a genetic disorder characterized by renal salt wasting. In this study, we found that MAGI-1 anchors Kir4.1 channels (Kir4.1 homomer and Kir4.1/Kir5.1 heteromer) and contributes to basolateral K(+) recycling. The Kir4.1 A167V mutation associated with EAST/SeSAME syndrome caused mistrafficking of the mutant channels and inhibited their expression on the basolateral surface of tubular cells. These findings suggest mislocalization of the Kir4.1 channels contributes to renal salt wasting.

Does a proton pump inhibitor cause hypokalemia?

Proton pump inhibitors (PPIs) act only in the stomach, although the proton pump, H(+),K(+)-ATPase exists and contributes to H(+) and K(+) homeostasis in the kidney. We encountered two hypokalemic cases receiving omeprazole. These cases were women ages 69 and 80 years old. Their serum potassium levels decreased with accelerated urinary potassium excretion with the use of omeprazole, and recovered by potassium-supplement and the discontinuation of omeprazole. Because inhibitory effects of PPIs on H(+),K(+)-ATPase are exerted only in acidic condition, hypokalemia is not generally introduced by PPIs alone. However, in extreme alkalosis or impaired K(+)-recycling system, PPIs may cause hypokalemia unrelated to hypomagnesemia.