Calcium transport in the rabbit superficial proximal convoluted tubule.

Calcium transport was studied in isolated S2 segments of rabbit superficial proximal convoluted tubules. 45Ca was added to the perfusate for measurement of lumen-to-bath flux (JlbCa), to the bath for bath-to-lumen flux (JblCa), and to both perfusate and bath for net flux (JnetCa). In these studies, the perfusate consisted of an equilibrium solution that was designed to minimize water flux or electrochemical potential differences (PD). Under these conditions, JlbCa (9.1 +/- 1.0 peq/mm X min) was not different from JblCa (7.3 +/- 1.3 peq/mm X min), and JnetCa was not different from zero, which suggests that calcium transport in the superficial proximal convoluted tubule is due primarily to passive transport. The efflux coefficient was 9.5 +/- 1.2 X 10(-5) cm/s, which was not significantly different from the influx coefficient, 7.0 +/- 1.3 X 10(-5) cm/s. When the PD was made positive or negative with use of different perfusates, net calcium absorption or secretion was demonstrated, respectively, which supports a major role for passive transport. These results indicate that in the superficial proximal convoluted tubule of the rabbit, passive driving forces are the major determinants of calcium transport.     

Glucocorticoids stimulate rabbit proximal convoluted tubule acidification.

Glucocorticoids have an important role in renal acidification; however, a direct effect of glucocorticoids on proximal convoluted tubule (PCT) acidification has not been directly demonstrated. In the present in vitro microperfusion study PCT from animals receiving dexamethasone (600 micrograms/kg twice daily for 2 d and 2 h before killing) had a significantly higher rate of bicarbonate absorption than did controls (92.0 +/- 13.3 vs 59.9 +/- 3.2 pmol/mm.min, P < 0.01). To examine if glucocorticoids had a direct epithelial action, dexamethasone was added to the bath of PCT perfused in vitro. After 3 h of incubation in paired experiments 10(-6) M and 10(-5) M dexamethasone resulted in an approximately 30% stimulation in the rate of bicarbonate absorption. 10(-7) M dexamethasone and 10(-6) M aldosterone had no effect on bicarbonate absorption. The stimulation of acidification by 10(-5) M dexamethasone was blocked by actinomycin D and cycloheximide. These data are consistent with a direct effect of glucocorticoids on PCT acidification, and this effect is dependent upon protein synthesis.     

Neonatal rabbit juxtamedullary proximal convoluted tubule acidification.

The present in vitro microperfusion study examined apical membrane Na+/H+ antiporter and basolateral membrane Na(HCO3)3 symporter activity in newborn and adult juxtamedullary proximal convoluted tubules. Proton fluxes were determined from the initial rate of change of intracellular pH after a change in the luminal or bathing solution, buffer capacity, and tubular volume of newborn and adult tubules. Intracellular pH (pHi) was measured fluorometrically using the pH-sensitive dye (2',7')-bis (carboxyethyl)-(5,6)-carboxyfluorescein (BCECF). Apical Na+/H+ antiporter proton flux, assayed by the effect of sodium removal (147----0 meq/liter) on pHi, was one-third the adult level for the first 2 wk and doubled in the 3rd wk of life. Adult levels were achieved by 6 wk of age. Na+/H+ antiporter activity was not detected on the basolateral membrane of 1-wk-old newborns, indicating that polarity of this transporter was already present. Basolateral membrane Na(HCO3)3 proton flux, assayed by the effect of a bath bicarbonate change (25----5 meq/liter) and by a bath sodium change (147----0 meq/liter) on pHi, was 50-60% of adult values in 1-wk-old newborns. Basolateral membrane Na(HCO3)3 proton flux assayed by a bath bicarbonate change (25----5 meq/liter) remained at 50-60% of adult values for the 1st mo of life and increased to adult levels by 6 wk of age. This transporter not only plays a role in net acidification, but is an important determinant of cell pH in newborn juxtamedullary proximal convoluted tubules.     

Flow dependence of transtubular potential difference in isolated perfused segments of rabbit proximal convoluted tubule

Transmembrane potential difference (pd) was studied in isolated perfused segments of rabbit proximal convoluted tubules. At perfusion flow rates above 10 nl/min the pd was -5.80 +/-0.3 mv (lumen negative) when perfusing with isosmolal ultrafiltrate of same rabbit serum as the bath. That this pd is generated by transport activity of the tubule is supported by three separate observations: (a) pd reversibly decreased with cooling from 37 degrees C to 25 degrees C; (b) pd decreased when 10(-5) M ouabain was added to the bath and reversed to control levels when ouabain was removed; and (c) heating to 47 degrees C irreversibly decreased pd to zero. The magnitude of the pd was related to perfusion flow rate at slower rates than 10 nl/min. A decrease in flow rate was associated with a decrease in pd. The tubular geometry and transmembrane hydrostatic pressure were ruled out as the mediating factors governing the magnitude of observed pd.     

Insulin stimulates volume absorption in the rabbit proximal convoluted tubule.

The present in vitro microperfusion study examined whether insulin affects volume absorption (Jv) in the proximal convoluted tubule (PCT). PCT were perfused with an ultrafiltrate-like solution and were bathed in a serum-like albumin solution. Addition of a physiologic concentration of 10(-10) M insulin to the bathing solution resulted in a stimulation of Jv and a more negative transepithelial potential difference (PD). There was a progressive stimulation of the lumen negative PD and Jv with higher insulin concentrations. Maximal stimulation occurred at 10(-8) M bath insulin. The insulin-induced stimulation of volume reabsorption was also observed when glucose and amino acids were removed from the luminal perfusate. Direct examination of the effect of insulin on glucose, chloride, and bicarbonate absorption demonstrated that the transport of all these solutes was stimulated by insulin. Addition of insulin to the luminal perfusate had no affect on Jv. These data show that insulin has a direct effect to stimulate Jv in the proximal tubule.     

Axial heterogeneity of intracellular pH in rat proximal convoluted tubule.

In the proximal convoluted tubule (PT), the HCO3- reabsorptive rate is higher in early (EPS) compared with late proximal segments (LPS). To examine the mechanism of this HCO3- reabsorption profile, intracellular pH (pHi) was measured along the superficial PT of the rat under free-flow and stationary microperfusion using the pH-sensitive fluorescence of 4-methylumbelliferone (4MU). With 4MU superfusion, pHi was found to decline along the PT. Observation with 365-nm excitation revealed that EPS were brightly fluorescent and always emerged away from their star vessel. Midproximal segments were darker and closer to the star vessel which was surrounded by the darkest LPS. Decreasing luminal HCO3- from 15 to 0 mM lowered pHi in both EPS and LPS, but pHi remained more alkaline in EPS with both perfusates. Thus the axial decline in pHi along the PT is due to both luminal factors and intrinsic differences in luminal H+ extrusion in PT cells.     

Intracellular cystine loading inhibits transport in the rabbit proximal convoluted tubule.

Cystinosis is an autosomal recessive disorder characterized by a high intracellular cystine concentration. To establish an in vitro model of this disorder and examine the mechanism of the proximal tubule transport defect seen with elevated intracellular cystine concentrations, rabbit proximal convoluted tubules (PCT) were perfused in vitro. PCTs were loaded with cystine using cystine dimethyl ester, a permeative methyl ester derivative. Bath cystine dimethyl ester (0.5 mM) reduced volume absorption (Jv) (0.67 +/- 0.07 to 0.15 +/- 0.09 nl/mm.min, P less than 0.01), bicarbonate transport (JTCO2) (47.2 +/- 4.9 to 11.1 +/- 2.8 pmol/mm.min, P less than 0.001) and glucose transport (JGLU) (34.1 +/- 1.5 to 19.7 +/- 1.5 pmol/mm.min, P less than 0.001). The methyl esters of leucine (0.5 mM), and tryptophan (0.5 and 2.0 mM) had no effect on these parameters. To examine if intracellular reduction of cystine to cysteine could contribute to the inhibition in transport, the effect of bath cysteine methyl ester on proximal tubular transport was examined. Bath cysteine methyl ester (2 but not 0.5 mM) resulted in an inhibition in Jv, JGLU, and JTCO2. Cystine dimethyl ester had no effect on mannitol or bicarbonate permeability. These data are consistent with intracellular proximal tubular cystine accumulation resulting in an inhibition of active transport.     

Modulation of phosphate absorption by calcium in the rabbit proximal convoluted tubule.

Proximal convoluted (S2) and straight (S3) renal tubule segments were studied to determine the effect of Ca on lumen-to-bath phosphate flux (JlbPO4). Increasing bath and perfusate Ca from 1.8 to 3.6 mM enhanced JlbPO4 from 3.3 +/- 0.7 to 6.6 +/- 0.6 pmol/mm per min in S2 segments (P less than 0.001) but had no effect in S3 segments. Decreasing bath and perfusate Ca from 1.8 to 0.2 mM reduced JlbPO4 from 3.7 +/- 0.6 to 2.2 +/- 0.6 in S2 segments. These effects were unrelated to changes in fluid absorption and transepithelial potential difference. Increasing cytosolic Ca with a Ca ionophore, inhibiting the Ca-calmodulin complex with trifluoperazine, or applying the Ca channel blocker nifedipine had no effect on JlBPO4 in S2 segments. Increasing only bath Ca from 1.8 to 3.6 mM did not significantly affect JlbPO4. However, increasing only perfusate Ca enhanced JlbPO4 from 3.4 +/- 0.7 to 6.1 +/- 0.7 pmol/mm per min (P less than 0.005). Inhibition of hydrogen ion secretion, by using a low bicarbonate, low pH perfusate, both depressed base-line JlbPO4 and abolished the stimulatory effect of raising perfusate Ca. Net phosphate efflux (JnetPO4) also increased after ambient calcium levels were raised, ruling out a significant increase in PO4 backflux. When net sodium transport was abolished by reducing the bath temperature to 24 degrees C, JnetPO4 at normal ambient calcium was reduced and increasing ambient calcium failed to increase it, ruling out a simple physicochemical reaction wherein phosphate precipitates out of solution with calcium. The present studies provide direct evidence for a stimulatory effect of Ca on sodium-dependent PO4 absorption in the proximal convoluted tubule, exerted at the luminal membrane. It is postulated that Ca modulates the affinity of the PO4 transporter for the anion.     

Ammonia transport by early and late proximal convoluted tubule of the rat.

Free-flow micropuncture experiments were performed to examine ammonia transport separately in early and late proximal convoluted tubule (PCT) of the rat. In control rats, ammonia was secreted along the early PCT but was reabsorbed along the late PCT. In rats with chronic metabolic acidosis, ammonia secretion along the early PCT was increased compared with controls, and ammonia absorption by the late PCT was converted to small net ammonia secretion. In the acidotic rats, ammonia secretion rate in the early PCT was six times higher than that in the late PCT. Thus, most or all of ammonia secretion by the PCT occurred along its early portion. In control and acidotic rats, luminal NH3 concentration in the early PCT was significantly higher than that in the late PCT, indicating that ammonia is not in diffusion equilibrium throughout the renal cortex. It is proposed that differences in ammonia transport rate in early vs. late PCT may be due to differences in ammonia production rate and/or to differences in the rate of an ammonia backflux that detracts from net ammonia secretion.     

Angiotensin II: a potent regulator of acidification in the rat early proximal convoluted tubule.

The early proximal convoluted tubule (PCT) is the site of 50% of bicarbonate reabsorption in the nephron, but its control by angiotensin II has not been previously studied. In vivo microperfusion was used in both the early and late PCT in Munich-Wistar rats. Systemic angiotensin II administration (20 ng/kg X min) or inhibition of endogenous angiotensin II activity with saralasin (1 microgram/kg X min) caused profound changes in bicarbonate absorption in the early PCT (169 +/- 25 and -187 +/- 15 peq/mm X min, respectively). Because the bicarbonate absorptive capacity of the early PCT under free-flow conditions is 500 peq/mm X min, angiotensin II administration or inhibition affected greater than 60% of proton secretion in this segment. Both agents less markedly affected bicarbonate absorption in the late PCT (+/- 28 peq/mm X min) or chloride absorption (+/- 68-99 peq/mm X min) in both the early and late PCT. Because of its potential for controlling the majority of bicarbonate absorption in the early PCT (hence greater than or equal to 30% of bicarbonate absorption in the entire nephron), angiotensin II may be a powerful physiologic regulator of renal acidification.     

Effect of cisplatin on proximal convoluted and straight segments of the rat kidney

The immediate effect of cisplatin on rat proximal tubular function was investigated by two different methods, the lithium clearance method and the occlusion time-transit time method (TT-OT). Within minutes after administration of cisplatin a significant increase in lithium clearance, fractional lithium clearance (CLi/Cin) and e-TT/OT was observed (from 270 +/- 32 to 387 +/- 60 microliters/min/g kidney weight, 0.202 +/- 0.03 to 0.340 +/- 0.06 and 0.415 +/- 0.02 to 0.497 +/- 0.02, respectively). These increases indicate an increased fluid delivery from both the proximal straight segment and the late proximal convoluted tubule after cisplatin administration. Concomitantly absolute proximal reabsorption rate was significantly decreased. Intervention by saline loading (2% of body weight) did not prevent the increase in e-TT/OT, but the increase in CLi/Cin was significantly less than in the control group. This finding suggests that saline loading protects either the pars recta of the proximal tubule or the juxtamedullary nephrons. Thus, cisplatin-induced nephrotoxicity in the rat is initiated by an acute mainly proximal tubular impairment including both pars convoluta and pars recta of the proximal tubule.     

Defective dopamine-1 receptor adenylate cyclase coupling in the proximal convoluted tubule from the spontaneously hypertensive rat.

The natriuretic effect of DA-1 agonists is less in the spontaneously hypertensive rat (SHR) than its normotensive control, the Wistar-Kyoto rat (WKY). To determine a mechanism of the decreased effect of DA-1 agonists on sodium transport, DA-1 receptors in renal proximal convoluted tubule (PCT) were studied by radioligand binding and by adenylate cyclase (AC) determinations. Specific binding of 125I-SCH 23982 (defined by 10 microM SCH 23390, a DA-1 antagonist) was concentration dependent, saturable, and stereoselective. The dissociation constant, maximum receptor density, and DA-1 antagonist inhibition constant were similar in SHR and WKY. The apparent molecular weight of the DA-1 receptor determined by the photoaffinity D1 probe 125I-MAB was also similar in WKY and SHR. However, DA-1 agonists competed more effectively for specific 125I-SCH 23982 binding sites in WKY than in SHR. Basal as well as forskolin, parathyroid hormone, GTP and Gpp(NH)p-stimulated-AC activities were similar. In contrast DA-1 agonists (fenoldopam, SKF 38393, SND 911C12) stimulated AC activity to a lesser extent in SHR. GTP and Gpp(NH)p enhanced the ability of DA-1 agonists to stimulate AC activity in WKY but not in SHR. These data suggest a defect in the DA-1 receptor-second messenger coupling mechanism in the PCT of the SHR.     

Cell pH in the rat proximal convoluted tubule. Regulation by luminal and peritubular pH and sodium concentration.

To examine the relative roles of apical and basolateral membrane transport mechanisms in the regulation of cell pH in the proximal convoluted tubule, cell pH was measured in the in vivo microperfused rat tubule using fluorescence. Decreasing luminal pH by 0.7 pH units caused cell pH to decrease by 0.08 pH units, whereas a similar decrease in peritubular pH caused cell pH to decrease by 0.32 pH units. Inhibition of basolateral membrane bicarbonate transport with peritubular 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonate (SITS) enhanced the response to luminal fluid acidification. Removal of luminal sodium caused a small transient acidification which was followed by a late alkalinization. Peritubular SITS increased the magnitude of the transient acidification, and eliminated the late alkalinization. The acidification was partially inhibited by luminal amiloride. The results demonstrate sodium-coupled processes on both the apical (Na/H antiport) and basolateral (Na/HCO3 symport) membranes. Basolateral membrane transporters are more important determinants of cell pH.     

Evidence for neutral transcellular NaCl transport and neutral basolateral chloride exit in the rabbit proximal convoluted tubule.

The electrical nature of active NaCl transport and the significance of a basolateral membrane chloride conductance were examined in isolated perfused rabbit proximal convoluted tubules (PCT). PCT were perfused with a high chloride solution that simulated late proximal tubular fluid and were bathed in an albumin solution that simulated rabbit serum in the control and recovery periods. The electrical nature of NaCl transport was examined by bathing the tubules in a high chloride albumin solution where there were no anion gradients. Volume reabsorption (Jv) during the control and recovery period was 0.56 and 0.51 nl/mm X min, respectively, and 0.45 nl/mm X min when the tubules were bathed in a high chloride bath. The transepithelial potential difference (PD) during the control and recovery periods averaged 2.3 mV, but decreased to 0.0 mV in the absence of anion gradients, which indicated that NaCl transport is electroneutral. Further evidence that NaCl transport is electroneutral was obtained by examining the effect of addition of 0.01 mM ouabain in PCT perfused and bathed with high chloride solutions. The Jv was 0.54 nl/mm X min in the control period and not statistically different from zero after inhibition of active transport. The PD was not different from zero in both periods. Two groups of studies examined the role of basolateral membrane Cl- conductance in NaCl transport. First, depolarizing the basolateral membrane with 2 mM bath Ba++ did not significantly affect Jv or PD. Second, the effect of the presumptive Cl- conductance inhibitor anthracene-9-CO2H was examined. Anthracene-9-CO2H did not significantly affect Jv or PD. In conclusion, these data show that NaCl transport in the PCT is electroneutral and transcellular and provide evidence against a significant role for basolateral membrane chloride conductance in the rabbit PCT.     

Effects of growth hormone and insulin-like growth factor I on rabbit proximal convoluted tubule transport.

This in vitro microperfusion study examined the effects of growth hormone and insulin-like growth factor I (IGF-I) on proximal convoluted tubule (PCT) transport. Tubules were perfused with an ultrafiltrate-like solution and bathed in a serum-like albumin solution. Neither a physiologic (5 x 10(-10) M), nor a pharmacologic (5 x 10(-8) M) dose of growth hormone had an effect on PCT phosphate or bicarbonate transport, or volume absorption. Addition of 5 x 10(-9) M and 5 x 10(-8) M IGF-I, but not 5 x 10(-10) M IGF-I, to the bathing solution resulted in an increase (12-15%) in phosphate transport, but no change in volume absorption or bicarbonate transport. Addition of IGF-I to the luminal perfusate also stimulated phosphate transport. The effect was noted at a concentration of 5 x 10(-11) M IGF-I (27% stimulation) and was maximal at a concentration of 5 x 10(-10) M IGF-I (46% stimulation). There was no effect of luminal IGF-I on volume absorption or bicarbonate transport. These data indicate that growth hormone has no direct effect on PCT transport. In the PCT, IGF-I stimulates phosphate transport specifically and acts via both basolateral and apical membranes. However, the magnitude of the maximal response to the luminal addition of IGF-I was threefold greater than that measured upon addition of the hormone to the bath, and the stimulation occurred at a 100-fold lower concentration. These data are consistent with IGF-I mediating the in vivo stimulation of phosphate transport by growth hormone.     

A functional comparison of the cortical collecting tubule and the distal convoluted tubule.

Electrical and permeability features of the distal convoluted tubule (DCT) and the cortical collecting tubule (CCT) were examined using the technique in which isolated segments of rabbit tubules were perfused in vitro. When rabbits were given a regular diet and tubules were perfused and bathed in artificial solutions simulating plasma ultrafiltrate, the potential difference (PD) was +3.7 plus or minus 1.9 mV in the CCT and -40.4 plus or minus 2.8 mV in the DCT. When rabbits were given a low sodium, high potassium diet plus i.m. deoxycorticosterone acetate (DOCA) (1 mg/kg per day), the PD in both the CCT (-30.8 plus or minus 3.9 mV) and the DCT (-33.8 plus or minus 5.5 mV) was negative. The PD in the CCT was quantitatively similar to that of diet plus DOCA when animals were given DOCA alone. The PD in both segments was inhibited by ouabain (10-minus 5 M) in the bath or by amiloride (10-minus 5 M) in the perfusate. Addition of vasopressin (200 muU/ml) to the bath caused a gradual decline of PD to zero in the CCT but failed to produce a potential response in the DCT. Osmotic water permeability was essentially zero in both segments in the absence of vasopressin. After addition of the vasopressin to the bath, osmotic water permeability in the DCT remained zero but increased to 71.9 plus or minus 25.5 X 10-minus 7 cm/s per atm in the CCT. We conclude that both segments are similar in that each possesses an electrogenic transport process but that these segments differ in that: (a) the CCT requires either exogenous or endogenous mineralocorticoid to maintain a maximal negative PD, whereas the PD in the DCT appears to be independent of mineralocorticoid effect; and (b) the CCT responds to vasopressin with a marked rise in water permeability, whereas the DCT is impermeable to water before and after addition of vasopressin.     

Regulation of cell pH by ambient bicarbonate, carbon dioxide tension, and pH in the rabbit proximal convoluted tubule.

To study the regulation of cell pH by ambient pH, carbon dioxide tension (PCO2), and bicarbonate (HCO3), cell pH was measured in the isolated, in vitro microperfused rabbit proximal convoluted tubule using the fluorescent dye (2',7')-bis-(carboxyethyl)-(5,6)-carboxyfluorescein. For the same changes in external pH, changes in [HCO3] and PCO2 affected cell pH similarly ([HCO3]: pHi/pHe = 0.67, PCO2: pHi/pHe = 0.64, NS). Isohydric changes in extracellular [HCO3] and PCO2 did not change cell pH significantly. Changes in peritubular [HCO3] elicited larger changes in cell pH than changes in luminal [HCO3], which were enhanced by peritubular 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonate (SITS). The cell pH defense against acute increases and decreases in PCO2 was inhibited by sodium, but not by chloride removal. Peritubular SITS inhibited the cell pH defense against increases and decreases of PCO2, whereas luminal amiloride inhibited cell pH defense against increases in PCO2. Conclusions: (a) Steady-state cell pH changes in response to changes in extracellular [HCO3] and PCO2 are quantitatively similar for a given change in extracellular pH; (b) the rate of the basolateral Na/(HCO3)3 cotransporter is a more important determinant of cell pH than the rate of the apical membrane mechanism(s); (c) cell pH defense against acute changes in PCO2 depends on the basolateral Na/(HCO3)3 cotransporter (acid and alkaline loads) and the luminal Na/H antiporter (acid loads).     

Sodium, phosphate, glucose, bicarbonate, and alanine interactions in the isolated proximal convoluted tubule of the rabbit kidney.

Interactions among the transport systems involved with sodium, bicarbonate, glucose, phosphate, and alanine absorption in isolated segments of the rabbit proximal convoluted tubule were examined with radioisotopic techniques to measure glucose, phosphate, and fluid absorption rates. The composition of the perfusate and bath varied from normal, physiological fluids to fluids deficient in a single solute. The deletion of glucose from the perfusate increased the lumen-to-bath flux of phosphate from 5.51 +/- 1.15 to 8.32 +/- 1.34 pmol/mm-min (P less than 0.01). Similar changes occurred when glucose transport was inhibited by phlorizin 10 micron in the perfusate, The deletion of alanine from the perfusate increased the lumen-to-bath flux of phosphate from 6.55 +/- 1.08 to 9.00 +/- 1.30 pmol/mm-min (P less than 0.01) but did not affect glucose transport significantly, 80.1 +/- 10.1 vs. 72.5 +/- 5.4 pmol/mm-min. Replacement of intraluminal sodium with choline, elimination of potassium from the bath, and removal of bicarbonate from the lumen and bath each reduced glucose, phosphate, and fluid absorption. These data indicate that the proximal absorptive processes for glucose and for phosphate include elements that are dependent upon some function of sodium transport. Additionally, the effects on phosphate transport of deleting glucose or alanine occur independent of any changes in net sodium transport and are opposite the effects of deleting bicarbonate. These differences may relate to the observations that the transport of glucose and alanine is electrogenic while that of bicarbonate is not. Regardless of possible mechanisms, the data demonstrate that important changes in the absorption rates of different solutes handled significantly by the proximal convoluted tubule may occur in response to changes in specific components of proximal sodium transport.     

Genetic disorders of NaCl transport in the distal convoluted tubule

The distal convoluted tubule (DCT) reabsorbs 5-10% of filtered Na, and is an important site for regulation of Na balance. Additionally, the amount and composition of the tubular fluid that leaves the DCT affects H and K secretion in more distal nephrin segments. Mutations in five genes whose products are expressed in the DCT demonstrate these points and help to define the mechanisms by which the DCT contributes to control of electrolyte balance and volume. Loss of function mutations in the apical thiazide-sensitive NaCl cotransporter and the basolateral K channel Kir4.1, and activating mutations in the Ca-sensing receptor cause a phenotypically similar salt wasting syndrome. Mutation in two recently identified kinases, WNK1 and WNK4 cause a salt-retaining syndrome through increased apical expression of NaCl cotransporter. Recent studies indicate that these genes are important not only for understanding the physiology of the distal nephron, but that they and others may also contribute to blood pressure variation in the general population.