The large conductance, calcium-activated BK-α/β4 potassium channel, localized to the intercalated cells of the distal nephron, mediates potassium secretion during high potassium, alkaline diets. Here we determine whether BK-α/β4-mediated potassium transport is dependent on epithelial sodium channel (ENaC)-mediated sodium reabsorption. We maximized sodium-potassium exchange in the distal nephron by feeding mice a low sodium, high potassium diet. Wild type and BK-β4 knockout mice were maintained on low sodium, high potassium, alkaline diet or a low sodium, high potassium, acidic diet for 7–10 days. Wild type mice maintained potassium homeostasis on the alkaline but not acid diet. BK-β4 knockout mice could not maintain potassium homeostasis on either diet. During the last 12 hours of diet, wild type mice on either a regular, alkaline or an acid diet, or knockout mice on an alkaline diet were administered amiloride (an ENaC inhibitor). Amiloride enhanced sodium excretion in all wild type and knockout groups to similar values; however, amiloride diminished potassium excretion by 59% in wild type but only by 33% in knockout mice on an alkaline diet. Similarly, amiloride decreased the transtubular potassium gradient by 68% in wild type but only by 42% in knockout mice on an alkaline diet. Amiloride treatment equally enhanced sodium excretion and diminished potassium secretion in knockout mice on an alkaline diet and wild type mice on an acid diet. Thus, the enhanced effect of amiloride on potassium secretion in wild type compared to knockout mice on the alkaline diet, clarify a BK- α/β4-mediated potassium secretory pathway in intercalated cells driven by ENaC-mediated sodium reabsorption linked to bicarbonate secretion.

Antibiotic abuse can lead to antibiotic resistance, which is a severe problem in China. The purpose of this study is to evaluate the short-term effects of antimicrobial stewardship strategies, including formulary restriction, preauthorization, perioperative quinolone restriction, and control of total antibiotic consumption in the ICU at a tertiary hospital in China. After implementation of antimicrobial stewardship, the total antibiotic consumption in the ICU significantly decreased. The defined daily doses (DDDs) per 100 patient-days decreased from 197.65 to 143.41; however, the consumption of cephalosporins increased from 53.65 to 63.17 DDDs. Significant improvements in resistance to amikacin, gentamicin, ciprofloxacin, ofloxacin, ceftriaxone, ceftazidime, and piperacillin in Enterobacteriaceae and resistance to ceftazidime, imipenem, and meropenem in non-fermenting Gram-negative rods were observed. In addition, the initial use of no antibiotics or of a single antibiotic significantly increased (P<0.001) and the use of two antibiotics in combination significantly decreased (P<0.001). Our results demonstrate that implementation of antimicrobial stewardship in a short period in the ICU dramatically reduced antibiotic consumption and significantly improved antibiotic resistance, which leads to more reasonable antibiotic selections by ICU physicians.

Because of its cardio-protective effects, a low Na, high K diet (LNaHK) is often warranted in conjunction with diuretics to treat hypertensive patients. However, it is necessary to understand the renal handling of such diets in order to choose the best diuretic. Wild type (WT) or Renal Outer Medullary K channel (ROMK) knockout mice (KO) were given a regular (CTRL), LNaHK, or high K diet (HK) for 4–7 days. On LNaHK, mice treated with either IP furosemide for 12 hrs, or given furosemide in drinking water for 7 days, exhibited decreased K clearance. We used free-flow micropuncture to measure the [K+] in the early distal tubule (EDT [K+]) before and after furosemide treatment. Furosemide increased the EDT [K+] in WT on CTRL but decreased that in WT on LNaHK. Furosemide did not affect the EDT [K+] of KO on LNaHK or WT on HK. Furosemide-sensitive Na+ excretion was significantly greater in mice on LNaHK than those on CTRL or HK. Patch clamp analysis of split-open TALs revealed that 70-pS ROMK exhibited a higher open probability (Po) but similar density in mice on LNaHK, compared with CTRL. No difference was found in the density or Po of the 30 pS K channels between two groups. These results indicate mice on LNaHK exhibited furosemide-sensitive net K+ secretion in the TAL that is dependent on increased NKCC2 activity and mediated by ROMK. We conclude that furosemide is a K-sparing diuretic by decreasing the TAL net K+ secretion in subjects on LNaHK.

A low Na, high K diet (LNaHK) is associated with a low rate of cardiovascular (CV) disease in many societies. Part of the benefit of LNaHK relies on its diuretic effects; however, the role of aldosterone (aldo) in the diuresis is not understood. LNaHK mice exhibit an increase in renal K secretion that is dependent on the large, Ca-activated K channel, (BK-α with accessory BK-β4; BK-α/β4). We hypothesized that aldo causes an osmotic diuresis by increasing BK-α/β4-mediated K secretion in LNaHK mice. We found that the plasma aldo concentration (P[aldo]) was elevated by 10-fold in LNaHK mice compared with control diet (Con) mice. We subjected LNaHK mice to either sham surgery (sham), adrenalectomy (ADX) with low aldo replacement (ADX-LA), or ADX with high aldo replacement (ADX-HA). Compared to sham, the urinary flow, K excretion rate, transtubular K gradient (TTKG), and BK-α and BK-β4 expressions, were decreased in ADX-LA, but not different in ADX-HA. BK-β4 knockout (β4KO) and WT mice exhibited similar K clearance and TTKG in the ADX-LA groups; however, in sham and ADX-HA, the K clearance and TTKG of β4KO were less than WT. In response to amiloride treatment, the osmolar clearance was increased in WT Con, decreased in WT LNaHK, and unchanged in β4KO LNaHK. These data show that the high P[aldo] of LNaHK mice is necessary to generate a high rate of BK-α/β4-mediated K secretion, which creates an osmotic diuresis that may contribute to a reduction in CV disease.

The gene SLC4A5 encodes the Na+-HCO3− co-transporter electrogenic 2 (NBCe2), which is located in the distal nephron. Genetically deleting NBCe2 (KO) causes Na+-retention and hypertension, a phenotype that is diminished with alkali loading. We performed experiments with acid-loaded mice and determined whether over-active epithelial Na+ channels (ENaC) or the Na+-Cl− co-transporter (NCC) causes the Na+ retention and hypertension in KO. In untreated mice, the mean arterial pressure (MAP) was higher in KO, compared with wild type (WT); however, treatment with amiloride, a blocker of ENaC, abolished this difference. In contrast, hydrochlorothiazide (HCTZ), an inhibitor of NCC, decreased MAP in WT, but not KO. Western blots showed that quantity of plasmalemmal full-length ENaC-α was significant higher in KO than in WT. Amiloride treatment caused a 2-fold greater increase in Na+ excretion in KO, compared with WT. In KO, but not WT, amiloride treatment decreased plasma [Na+] and urinary K+ excretion, but increased hematocrit and plasma [K+] significantly. Micropuncture with microelectrodes showed that the [K+] was significantly higher and the transepithelial potential (Vte) was significantly lower in the late distal tubule (LDT) of the KO compared with WT. The reduced Vte in KO was amiloride-sensitive and therefore revealed an upregulation of electrogenic ENaC-mediated Na+ reabsorption in this segment. These results show that, in the absence of NBCe2 in the LDT, acid-loaded mice exhibit disinhibition of ENaC-mediated Na+ reabsorption, which results in Na+ retention, K+ wasting, and hypertension.