Hangil Chang

Association between activating mutations of calcium-sensing receptor and Bartter's syndrome

Bartters syndrome is a heterogeneous disorder characterised by deficient renal reabsorption of sodium and chloride, and hypokalaemic metabolic alkalosis with hyper-reninaemia and hyperaldosteronaemia. Mutations in several ion transporters and channels have been associated with the pathogenesis of Bartters syndrome. We describe two hypocalcaemic patients with deficient parathyroid hormone secretion who also showed characteristics of Bartters syndrome. We found activating mutations of the gene for the calcium-sensing receptor (CASR) in both patients. Activation of this calcium-sensing receptor inhibits the activity of a renal outer-medullary potassium channel that is mutated in type 2 Bartters syndrome. We therefore suggest that some activating mutations of CASR could provide new mechanisms for the development of Bartters syndrome.

Lack of mutations in epithelial sodium channel beta-subunit gene in human subjects with hypertension.

Objective To investigate a possible role for mutations of the epithelial sodium channel in patients with essential hypertension. Design A cross-sectional study screening essential hypertension patients and normotensive controls for the presence of a genetic abnormality in the epithelial sodium channel β -subunit in the Japanese population. Setting An institutional teaching hospital. Patients and participants Ninety Japanese patients with essential hypertension and 51 normotensive controls were investigated. The hypertensive patients were consecutive samples from our hypertension clinics. It was required that they had had a previous history of systolic blood pressure higher than 160 mmHg or diastolic higher than 95 mmHg. Secondary hypertension was excluded by clinical presentation or appropriate laboratory examinations. Normotensive subjects were patients visiting our outpatient clinics without evidence or a history of hypertension. It was required that they had systolic blood pressures less than 160 mmHg and diastolic blood pressures less than 90 mmHg, and that they were aged above 60 years. Interventions Genomic DNA from each subject was purified from whole blood and was used as the template for polymerase chain reaction amplification of the carboxyterminal portion of the epithelial sodium channel β-subunit. Amplified DNA segments were screened for genetic mutations by direct sequencing. Main outcome measure Genetic mutations of the epithelial sodium channel β -subunit. Results No No significant genetic mutation was detected in any of the hypertensive and normotensive subjects, except for a polymorphism found in three subjects (two hypertensives and one normotensive). Conclusion Mutations of the carboxy-terminal portion of the epithelial sodium channel β -subunit were not identified in an unselected cohort of patients with essential hypertension from the Japanese community.

A numerical model of the renal distal tubule

A numerical model of the rat distal tubule was developed to simulate water and solute transport in this nephron segment. This model incorporates the following: 1) Na-Cl cotransporter, K-Cl cotransporter, Na channel, K channel, and Cl channel in the luminal membrane; 2) Na-K-ATPase, K channel, and Cl channel in the basolateral membrane; and 3) conductances for Na, K, and Cl in the paracellular pathway. Transport rates were calculated using kinetic equations. Axial heterogeneity was represented by partitioning the model into two subsegments with different sets of model parameters. Model equations derived from the principles of mass conservation and electrical neutrality were solved numerically. Values of the model parameters were adjusted to minimize a penalty function that was devised to quantify the difference between model predictions and experimental results. The developed model could simulate the water and solute transport of the distal tubule in the normal state, as well as in conditions including thiazide or amiloride application and various levels of sodium load and tubular flow rate.

Hyperkalemia Due to Nafamostat Mesylate

To the Editor: Nafamostat mesylate (6-amidino-2-naphthyl p-guanidinobenzoate, dimethanesulfonate; molecular weight, 540) is a synthetic serine protease inhibitor that is widely used to treat acute ...

A kinetic model of the thiazide-sensitive Na-Cl cotransporter

The aim of this study was to construct a numerical model of the thiazide-sensitive Na-Cl cotransporter (TSC) that can predict kinetics of thiazide binding and substrate transport of TSC. We hypothesized that the mechanisms underlying these kinetic properties can be approximated by a state diagram in which the transporter has two binding sites, one for sodium and another for chloride and thiazide. On the basis of the state diagram, a system of linear equations that should be satisfied in the steady state was postulated. Numerical solution of these equations yielded model prediction of kinetics of thiazide binding and substrate transport. Rate constants, which determine transitional rates between states, were systematically adjusted to minimize a penalty function that was devised to quantitatively estimate the difference between model predictions and experimental results. With the resultant rate constants, the model could simulate the following experimental results: 1) dissociation constant of thiazide in the absence of sodium and chloride; 2) inhibitory effect of chloride on thiazide binding; 3) stimulatory effect of sodium on thiazide binding; 4) combined effects of sodium and chloride on thiazide binding; 5) dependence of sodium influx on extracellular sodium and chloride; and 6) inhibition of sodium influx by extracellular thiazide. We conclude that known kinetic properties of TSC can be predicted by a model which is based on a state diagram.The aim of this study was to construct a numerical model of the thiazide-sensitive Na-Cl cotransporter (TSC) that can predict kinetics of thiazide binding and substrate transport of TSC. We hypothesized that the mechanisms underlying these kinetic properties can be approximated by a state diagram in which the transporter has two binding sites, one for sodium and another for chloride and thiazide. On the basis of the state diagram, a system of linear equations that should be satisfied in the steady state was postulated. Numerical solution of these equations yielded model prediction of kinetics of thiazide binding and substrate transport. Rate constants, which determine transitional rates between states, were systematically adjusted to minimize a penalty function that was devised to quantitatively estimate the difference between model predictions and experimental results. With the resultant rate constants, the model could simulate the following experimental results: 1) dissociation constant of thiazide in the absence of sodium and chloride; 2) inhibitory effect of chloride on thiazide binding; 3) stimulatory effect of sodium on thiazide binding; 4) combined effects of sodium and chloride on thiazide binding; 5) dependence of sodium influx on extracellular sodium and chloride; and 6) inhibition of sodium influx by extracellular thiazide. We conclude that known kinetic properties of TSC can be predicted by a model which is based on a state diagram.

Ca2+-activated K+ conductance causes membrane hyperpolarizations in a monkey kidney cell line (JTC-12)

SummaryWe have previously reported hyperpolarizing membrane potential changes in a monkey kidney cell line (JTC-12) which has characteristics resembling proximal tubular cells. These hyperpolarizations could be observed spontaneously or evoked by mechanically touching adjacent cells. In this report, we have shown further evidence that these hyperpolarizations are elicited by an increase in membrane conductance to K+ which is caused by an increase in cytosolic Ca2+ concentration. In addition, we have found another type of hyperpolarization which is evoked by applying flow of extracellular fluid to the cell. Intracellular injection of Ca2+ and Sr2+ evoked hyperpolarizations, while intracellular injection of Mn2+ and Ba2+ did not. Intracellular injection of EGTA suppressed both spontaneous and mechanically evoked hyperpolarizations. In Ca2+-free medium, both spontaneous and flow-evoked hyperpolarizations were not observed, while mechanical stimuli consistently evoked hyperpolarization. In Na+-free medium, the incidence of cells showing the spontaneous or flow-evoked hyperpolarization increased, and the amplitude and the duration of the mechanically evoked hyperpolarization became greater. Quinidine inhibited all types of hyperpolarization. These data suggest that hyperpolarizations in JTC-12 cells are due to an increase in Ca2+-activated K+ conductance.

Hyperpolarizing membrane potential changes in a cloned monkey kidney cell line.

Electrophysiological properties of a cloned monkey kidney cell line, JTC-12, were studied. The mean resting potential and input resistance were −15.3 mV and 78 MΩ, respectively. Spontaneous hyperpolarizations with increased membrane conductance were observed. Similar hyperpolarization could be elicited by mechanical and electrical stimulations. The mean reversal potential of these hyperpolarizations was −72.7 mV. Hyperpolarization could be also elicited in a chloride-free solution. These data indicate that: (1) JTC-12 cells exhibit spontaneous and induced hyperpolarizations, and (2) occurrence of hyperpolarization is related to an increase in membrane permeability to potassium ions.

Serum hepatocyte growth factor concentration in patients with various degrees of chronic renal failure

Summary: Serum hepatocyte growth factor (HGF) concentrations were measured in healthy volunteers, chronic renal failure patients without renal replacement therapy and haemodialysis patients. Serum HGF concentrations in healthy volunteers, chronic renal failure patients and haemodialysis patients were 0.18 ± 0.04 (s.d.), 0.28 ± 0.06 and 0.46 ± 0.22 ng/mL, respectively. Serum HGF concentration in chronic renal failure patients was significantly higher than that in healthy volunteers. Serum HGF concentration in haemodialysis patients was significantly higher than those in healthy volunteers and chronic renal failure patients. There was no regression of serum HGF concentration on age, sex, history of haemodialysis, prehaemodialysis serum creatinine concentration, and serum tumour necrosis factor (TNF)‐α concentration. We conclude that chronic renal disease and haemodialysis therapy are contributing factors to an increased serum HGF concentration.

Effects of ubiquinones on spontaneous membrane hyperpolarizations in a cloned monkey kidney cell line

The effects of ubiquinones on spontaneous membrane hyperpolarizations in JTC-12 cells were examined. There were three types of spontaneous hyperpolarizations; rhythmic, sporadic and oscillatory types. The oscillatory type was not observed in the standard medium, whereas it was observed in sodium-free medium or in the medium containing 300 nM coenzyme Q10. The number of the cells showing spontaneous hyperpolarizations significantly increased in the medium containing coenzyme Q10 (47.7%) as compared to the control (18.9%). However, coenzyme Q1 (500 nM) showed no effects.