Accurate mRNA size determination in northern analysis using individual lane size markers.
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Animals↗
Biomedical subjects
J M Sands
Publications and source records attributed to J M Sands.
Active sodium-urea counter-transport is inducible in the basolateral membrane of rat renal initial inner medullary collecting ducts.
Rat inner medullary collecting ducts (IMCD3s) possess a luminal Na+-dependent, active urea secretory transport process, which is upregulated by water diuresis. In this study of perfused IMCDs microdissected from base (IMCD1), middle (IMCD2), or tip (IMCD3) of the inner medulla, we tested whether furosemide diuresis alters active urea transport. Rats received furosemide (10 mg/d s.c. for 3-4 d) and were compared with pair-fed control rats. Furosemide significantly decreased urine osmolality and urea clearance, and increased blood urea nitrogen. IMCD3s from furosemide-treated rats had significantly lower rates of active urea secretion than IMCD3s from control rats. IMCD2s showed no active urea transport in control or furosemide-treated rats. IMCD1s from control rats had no active urea transport, but IMCD1s from furosemide-treated rats expressed significant rates of active urea reabsorption. In IMCD1s, this active urea reabsorptive transport process was inhibited by: (i) 0. 25 mM phloretin (bath); (ii) 1 mM ouabain (bath); and (iii) replacing bath Na+ with NMDG+; it was stimulated by 10 nM bumetanide (bath). In summary, we found that furosemide decreased active urea secretion in IMCD3s and induced active urea reabsorption in IMCD1s. The new Na+- dependent, active urea reabsorptive transport process may be a basolateral Na+-urea antiporter.
Amiloride↗
Evidence for sodium-dependent active urea secretion in the deepest subsegment of the rat inner medullary collecting duct.
Active reabsorption of urea appears in the initial IMCD (IMCD1) of rats fed a low-protein diet. To determine whether active urea transport also occurs in the deepest IMCD subsegment, the IMCD3, we isolated IMCDs from the base (IMCD1), middle (IMCD2), and tip (IMCD3) regions of the inner medulla from rats fed a normal protein diet and water ad libitum. IMCDs were perfused with identical perfusate and bath solutions. A significant rate of net urea secretion was present only in IMCD3s. Replacing perfusate Na+ with NMDG+ reversibly inhibited net urea secretion but replacing bath Na+ with NMDG+ or perfusate Cl- with gluconate- had no effect. Net urea secretion was significantly inhibited by: (a) 250 microM phloretin (perfusate); (b) 100 nM triamterene (perfusate); (c) 1 mM ouabain (bath); and (d) cooling the tubule to 23 degrees C. Net urea secretion was significantly stimulated by 10 nM vasopressin (bath). Next, we perfused IMCD3s from water diuretic rats (given food ad libitum) and found a significant, fivefold increase in net urea secretion. In summary, we identified a secondary active, secretory urea transport process in IMCD3s of normal rats which is upregulated in water diuretic rats. This new urea transporter may be a sodium- urea antiporter.
Animals↗
Effect of age and testosterone on the vasopressin response to dehydration in F344BNF1 male rats.
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Aging↗
Immunolocalization of phospholipase C isoforms in rat kidney.
BACKGROUND: Phospholipase C (PLC) is an important factor in signal transduction because this enzyme is activated by several hormones and growth factors. Eight PLC isoforms have been described raising the possibility that different cells express a single isoform or activate specific isoforms in different cells. Therefore, the goal of this study was to determine which PLC isoforms are expressed in specific regions of rat kidney. METHODS: Western blot analysis was performed in microdissected nephron segments of rat kidney, while immunohistochemical analysis was performed on whole rat kidney slices using PLC isoform-specific antibodies. RESULTS: All three families of PLC isoforms (beta, gamma, and delta) were present throughout the cortical and medullary regions of the kidney. Only the PLC-beta1 isoform was observed in the brush border of the proximal tubule, but all isoforms were present in glomeruli and in the cytoplasm of tubular epithelial cells. In addition, only the PLC-gamma1 isoform was expressed in the internal elastic lamina of the renal artery, while vasa recta expressed PLC-beta1 most intensely. Medullary thick ascending limbs showed an intense level of expression of all three isoforms. CONCLUSION: Multiple PLC isoforms are present in glomeruli, renal tubules, and renal vasculature in vivo, but with some segment-specific differences. These findings suggest that the response of a specific cell is not determined by expression of only one PLC isoform, with the exception of the brush border of the proximal tubule and the renal arteries. Instead, the presence of multiple PLC isoforms in specific regions of the kidney suggests that hormonal regulation in vivo involves mechanisms beyond cell-specific isoforms of PLC.
Animals↗
Vasopressin-elicited water and urea permeabilities are altered in IMCD in hypercalcemic rats.
To investigate how hypercalcemia blunts renal concentrating ability, alterations in basal and arginine vasopressin (AVP)-elicited osmotic water (Pf) and urea (Purea) permeabilities were measured in isolated perfused terminal inner medullary collecting ducts (IMCD) from control and chronically hypercalcemic rats after dihydrotachysterol (DHT) (M. Levi, L. Peterson, and T. Berl. Kidney Int. 23: 489-497, 1983) treatment. The IMCD Pf of DHT-treated rats did not increase significantly after AVP and was accompanied by a significant 87 +/- 4% reduction in aquaporin-2 (AQP-2) protein but not mRNA. In contrast, both basal and AVP-elicited IMCD Purea from DHT rats were significantly increased and accompanied by a significant 41 +/- 11% increase in AVP-regulated urea transporter protein content. Immunoblotting with anti-calcium/polyvalent cation-sensing receptor protein (CaR) antiserum revealed specific alterations in CaR bands in endosomes purified from the apical membranes of inner medulla of DHT rats. These data are the first detailed analyses of hypercalcemia-induced alterations in AVP-regulated permeabilities and membrane transporters in IMCD. We conclude that selective alterations in IMCD transport occur in hypercalcemia, permitting the body to dispose of excess calcium without forming calcium-containing renal stones.
Animals↗
Long-term regulation of renal urea transporter protein expression in rat.
To test the hypothesis that the abundance of the apical urea transporter of the inner medullary collecting duct (IMCD) is regulated in vivo by factors associated with altered water balance, immunoblots of rat inner medullary membrane fractions were probed with rabbit polyclonal antibodies against the renal urea transporter (RUT) gene product. In inner medullas of Brattleboro rats, which manifest severe chronic water diuresis, a 117-kD band was seen, in addition to the previously described 97-kD band. These two bands were detectable by antibodies directed against two different regions of the RUT sequence. When Brattleboro rats were treated with a 5-d infusion of arginine vasopressin (AVP) by osmotic minipump, the 117-kD band was markedly diminished, whereas the 97-kD band was unchanged. Simultaneous infusion of the diuretic agent furosemide prevented the AVP-induced decrease in the 117-kD band. In AVP-infused Sprague Dawley rats, the 117-kD band was barely perceptible. However, when AVP-treated rats were infused with furosemide for 5 d, the 117-kD band was markedly accentuated, whereas the 97-kD band was unchanged. The abundance of the 117-kD RUT protein in the renal papilla was inversely correlated with dietary protein intake. Further immunoblotting studies revealed that the 117-kD protein is heavily expressed in IMCD cells and not in non-collecting duct components of the inner medulla, and is present in low-density microsome fractions from inner medulla. From this study, the following conclusions can be made: (1) The collecting duct urea transporter is present in at least two forms (97 and 117 kD) in the IMCD. (2) The expression level of the 117-kD urea transporter protein is regulated and is inversely correlated with medullary osmolality and urea concentration, but does not correlate with circulating AVP level. (3) Although AVP regulates RUT function on a short-term basis, long-term changes in AVP levels do not increase RUT abundance.
Animals↗
Long-term regulation of inner medullary collecting duct urea transport in rat.
Facilitated urea transport is regulated acutely by arginine vasopressin (AVP) and hyperosmolality in rat terminal inner medullary collecting duct (IMCD). This study tested whether chronic diuresis or antidiuresis regulates facilitated urea transport. Basal and AVP-stimulated urea permeabilities (Purea) were measured in perfused IMCD subsegments. Rats were made: (1) diuretic by giving them sugar water (with or without food) or furosemide; or (2) antidiuretic by water deprivation. They were then compared with untreated rats given food and water ad libitum. Terminal IMCD from untreated rats had a high basal Purea that was significantly increased by AVP. Diuresis significantly increased basal Purea in terminal IMCD in all five diuresis protocols. Water deprivation for 1 or 3 d had no effect on basal or AVP-stimulated Purea in the IMCD2 subsegment of the terminal IMCD. In contrast, 3 d of water deprivation significantly increased both basal and AVP-stimulated Purea in the IMCD3 subsegment; 1 d of water deprivation had no effect on basal or AVP-stimulated Purea. Next, initial IMCD (IMCD1) were studied. Initial IMCD from untreated rats had a low basal Purea that was not increased by AVP (10 nM). Water diuresis (with or without food) for 3 to 5 d had no effect on basal Purea but significantly increased AVP-stimulated Purea. Furosemide diuresis and water diuresis for 1 or 7 d had no effect on either basal or AVP-stimulated Purea in initial IMCD. Water deprivation for 2 to 3 d, but not for 1 d, significantly increased basal Purea in initial IMCD, whereas water deprivation for 1 d increased AVP-stimulated Purea. It is concluded that chronic changes in hydration cause heterogeneous changes in facilitated urea transport in rat IMCD subsegments.
Animal Feed↗
Apical extracellular calcium/polyvalent cation-sensing receptor regulates vasopressin-elicited water permeability in rat kidney inner medullary collecting duct.
During antidiuresis, increases in vasopressin (AVP)-elicited osmotic water permeability in the terminal inner medullary collecting duct (tIMCD) raise luminal calcium concentrations to levels (> or = 5 mM) above those associated with the formation of calcium-containing precipitates in the urine. Calcium/polycation receptor proteins (CaRs) enable cells in the parathyroid gland and kidney thick ascending limb of Henle to sense and respond to alterations in serum calcium. We now report the presence of an apical CaR in rat kidney tIMCD that specifically reduces AVP-elicited osmotic water permeability when luminal calcium rises. Purified tIMCD apical membrane endosomes contain both the AVP-elicited water channel, aquaporin 2, and a CaR. In addition, aquaporin 2-containing endosomes also possess stimulatory (G(alpha q)/G(alpha 11) and inhibitory (G(alpha i1, 2, and 3)) GTP binding proteins reported previously to interact with CaRs as well as two specific isoforms (delta and zeta) of protein kinase C. Immunocytochemistry using anti-CaR antiserum reveals the presence of CaR protein in both rat and human collecting ducts. Together, these data provide support for a unique tIMCD apical membrane signaling mechanism linking calcium and water metabolism. Abnormalities in this mechanism could potentially play a role in the pathogenesis of renal stone formation.
Animals↗
Bartter's syndrome, supraventricular tachycardia, mitral valve prolapse, and asthma: a therapeutic challenge.
A 25-year-old man with acquired Bartter's syndrome, mitral valve prolapse, and supraventricular tachycardia secondary to a low atrial focus was diagnosed with asthma. The unique aspects of managing these coexisting diseases are evaluated. Calculation of free-water clearance in the diagnosis of Bartter's syndrome and the etiology and characteristics of the syndrome are discussed.
Adult↗
Effect of aging on vasopressin and aquaporin responses to dehydration in Fischer 344-brown-Norway F1 rats.
The plasma vasopressin (VP) response to 72 h of water deprivation is attenuated in 30-mo-old Fischer 344 (F344) rats relative to 4-mo-old rats. This appears to reflect an inability to increase VP synthesis. In contrast, elevated plasma VP has been reported in the Brown-Norway (BN) strain of rats secondary to reduced renal VP responsivity. The response to dehydration in the F1 cross of these strains (F344BNF1) was evaluated. Male rats, 4 and 30 mo old, were deprived of water for 72 h or allowed water ad libitum. In response to dehydration, plasma sodium and hematocrit were significantly increased in both young and aged rats (P < 0.05), but plasma VP, urine osmolality, and aquaporin 2 expression were only increased in the young rats (P < 0.05). Posterior pituitary content of immunoreactive VP was depleted in the young but not the old rats. Thus the aged F344BNF1 rats demonstrated a deficit in VP release in response to an apparently similar dehydration stimulus. This deficit was different from those previously reported for either the F344 or BN strains. Thus further studies are required to determine the abnormalities underlying this response.
Aging↗
Urea transporters in kidney and erythrocytes.
Physiological and molecular data demonstrate that urea transport in kidney and erythrocytes is regulated by specific urea transporter proteins. The urea transporter in the terminal inner medullary collecting duct permits very high rates of regulated transepithelial urea transport and results in the delivery of large amounts of urea into the deepest portions of the inner medulla, where it is needed to maintain a high interstitial osmolality for concentrating the urine maximally. The urea transporter in erythrocytes permits these cells to lose urea rapidly as they ascend through the ascending vasa recta, thereby preventing loss of urea from the medulla. Urea lost from the medulla would decrease concentrating ability by decreasing the efficiency of countercurrent exchange, as occurs in individuals who lack the Kidd antigen. The recent cloning of cDNAs for these two urea transporters has begun to yield new insights into the mechanisms underlying acute and long-term regulation of urea transport and should permit exciting new insights in the future. This review focuses on the physiological and biophysical evidence that established the concept of urea transporters, the subsequent cloning of cDNAs for urea transporters, and the recent integrative studies into the regulation of urea transport. We also propose a new systematic nomenclature and a new structural model for urea transporters.
Amino Acid Sequence↗
Glucocorticoids mediate a decrease in AVP-regulated urea transporter in diabetic rat inner medulla.
Providing glucocorticoids to adrenalectomized (Adx) rats results in downregulation of the vasopressin (AVP)-regulated urea transporter (VRUT) in the renal inner medullary (IM) tip. To examine the physiological relevance of this response, we studied rats with uncontrolled diabetes mellitus induced by streptozotocin (STZ), since these rats have increased corticosterone production and urea excretion. We measured VRUT protein in extracts from the IM tip or base of pair-fed control and diabetic rats by Western analysis using an antibody to rat VRUT. In the IM tip, VRUT was significantly reduced by 39% in diabetic compared with control rats. In the IM base, there was no significant difference between diabetic and control rats. To determine whether the decrease in VRUT in the IM tip was mediated by glucocorticoids, the experiment was repeated using the following three groups of rats: 1) Adx alone, 2) Adx + STZ, and 3) Adx + STZ + replacement with a physiological dose of glucocorticoid. There was no significant difference in VRUT between Adx and Adx + STZ rats. However, VRUT was significantly reduced by 32% in the IM tip of glucocorticoid-treated Adx + STZ rats compared with control Adx + STZ rats. We conclude that glucocorticoids regulate the abundance of VRUT protein independently of insulin in diabetic rats.
Adrenalectomy↗
Safety and efficacy of low-dose subcutaneous erythropoietin in hemodialysis patients.
Anemia in hemodialysis patients is effectively treated by intravenous (IV) injections of recombinant human erythropoietin (rHuEPO) at each dialysis session. Because the hormone is effective by subcutaneous (SC) administration, it was decided that this study would evaluate low-dose weekly SC rHuEPO therapy. To determine the safety and efficacy of weekly SC rHuEPO administration to hemodialysis patients, only one third the weekly IV dose was given and the effects were compared with those from an age-, gender-, and nephrologic disease-matched control group treated in the standard fashion. Forty-four patients entered the trial and 27 completed the protocol along with 27 control subjects. During Phase 1, experimental and control subjects received standard IV rHuEPO at dialysis for 6 months. During Phase 2, experimental patients received weekly SC rHuEPO at one third the weekly IV dose for 10 months; control subjects continued to receive IV therapy. In Phase 3, both groups were treated for 6 more months with IV rHuEPO. In Phase 2, there was no significant reduction in hematocrit value, reticulocyte count, transferrin saturation, or ferritin level in the experimental group, even with only one third the weekly rHuEPO IV dose over the 10-month period. There were no significant differences between IV and SC rHuEPO administration or between experimental and control subjects in blood pressure, serum chemistries, or parameters of "dialysis adequacy." It was concluded that low-dose weekly SC rHuEPO administration is a safe and effective method for maintaining the hematocrit level of stable hemodialysis patients. This therapy could enhance the efficacy of rHuEPO and substantially reduce costs while preserving patient care outcomes.
Anemia↗
Glucocorticoids downregulate the vasopressin-regulated urea transporter in rat terminal inner medullary collecting ducts.
This study tested whether glucocorticoids regulate tubular urea transport. Urea permeability was measured in perfused inner medullary collecting duct (IMCD) subsegments from rats that underwent adrenalectomy, adrenalectomy plus replacement with a physiologic dose of glucocorticoid (dexamethasone), or sham operation. Compared with sham rats, basal urea permeability in terminal IMCD was significantly increased in adrenalectomized rats and reduced in dexamethasone-treated rats. Vasopressin significantly increased urea permeability in all three groups. In contrast, there was no difference in basal or vasopressin-stimulated urea permeability in initial IMCD between the three groups. Next, membrane and vesicle fraction proteins were isolated from inner medullary tip or base and Western analysis was performed by use of an antibody to the rat vasopressin-regulated urea transporter. Vasopressin-regulated urea transporter protein was significantly increased in both membrane and vesicle fractions from the inner medullary tip of adrenalectomized rats. There was no change in vasopressin-regulated urea transporter protein in the inner medullary base, and Northern analysis showed no change in urea transporter mRNA abundance in either inner medullary region. It was concluded that glucocorticoids can downregulate function and expression of the vasopressin-regulated urea transporter in rat terminal IMCD.
Adrenalectomy↗
Changes in aquaporin-2 protein contribute to the urine concentrating defect in rats fed a low-protein diet.
Low-protein diets cause a urinary concentrating defect in rats and humans. Previously, we showed that feeding rats a low (8%) protein diet induces a change in urea transport in initial inner medullary collecting ducts (IMCDs) which could contribute to the concentrating defect. Now, we test whether decreased osmotic water permeability (Pf) contributes to the concentrating defect by measuring Pf in perfused initial and terminal IMCDs from rats fed 18 or 8% protein for 2 wk. In terminal IMCDs, arginine vasopressin (AVP)-stimulated osmotic water permeability was significantly reduced in rats fed 8% protein compared to rats fed 18% protein. In initial IMCDs, AVP-stimulated osmotic water permeability was unaffected by dietary protein. Thus, AVP-stimulated osmotic water permeability is significantly reduced in terminal IMCDs but not in initial IMCDs. Next, we determined if the amount of immunoreactive aquaporin-2 (AQP2, the AVP-regulated water channel) or AQP3 protein was altered. Protein was isolated from base or tip regions of rat inner medulla and Western analysis performed using polyclonal antibodies to rat AQP2 or AQP3 (courtesy of Dr. M.A. Knepper, National Institutes of Health, Bethesda, MD). In rats fed 8% protein (compared to rats fed 18% protein): (a) AQP2 decreases significantly in both membrane and vesicle fractions from the tip; (b) AQP2 is unchanged in the base; and (c) AQP3 is unchanged. Together, the results suggest that the decrease in AVP-stimulated osmotic water permeability results, at least in part, in the decrease in AQP2 protein. We conclude that water reabsorption, like urea reabsorption, responds to dietary protein restriction in a manner that would limit urine concentrating capacity.
Animals↗
Active urea transport in the rat inner medullary collecting duct: functional characterization and initial expression cloning.
Active transport of urea has been proposed to exist in the inner medullary collecting duct (IMCD) of low-protein fed mammals for over 30 years. We perfused IMCD subsegments from rats fed a standard (18%) or a low (8%) protein diet and tested for the presence of active urea transport. We found no active urea transport in terminal IMCDs, regardless of diet. In initial IMCDs from rats fed 18% protein or fed 8% protein for one to two weeks, we again found no active urea transport. However, in rats fed 8% protein for three to four weeks, we found significant net urea reabsorption. This active urea reabsorption was inhibited when Na+, K(+)-ATPase activity was inhibited by adding 1 mM ouabain or removing bath potassium, suggesting a secondary active transport process. Removing sodium from the perfusate completely inhibited net urea reabsorption, demonstrating that this active urea transport is dependent upon the presence of sodium in the tubule lumen. Unlike the facilitated urea transporter, the active urea transporter was not inhibited by phloretin nor stimulated by vasopressin, suggesting that it is a distinct transport protein. To test this hypothesis, we size-separated poly(A)(+)-RNA prepared from inner medullae of rats fed 8% protein for three weeks and injected it into Xenopus laevis oocytes. RNA from a 4.4 to 8.4 kb size fraction increased urea permeability fourfold compared to water-injected oocytes or injecting RNA from other size-fractions. We conclude that feeding rats a low-protein diet for three weeks induces the expression of an unique, secondary active, sodium-dependent urea transporter whose cDNA is between 4.4 and 8.4 kb in size. In addition, our results suggest that it will be possible to clone the cDNA for this sodium-urea cotransporter by expression in Xenopus laevis oocytes.
Animals↗
Current concepts of the countercurrent multiplication system.
The production of a concentrated urine is achieved by countercurrent multiplication in the renal medulla. While the single effect in the outer medulla is known to be active NaCl reabsorption in the thick ascending limb, the single effect in the inner medulla is not definitively established. However, the passive model of Kokko and Rector [1] and Stephenson [2] remains the most widely accepted mechanism for the single effect in the inner medulla. Continued experimental studies of transport in perfused inner medullary nephron segments and mathematical simulations that incorporate these new experimental values and anatomic complexity will be needed to fully elucidate the process of urinary concentration. In addition, the availability of molecular reagents will permit investigation into the molecular mechanisms that regulate transport proteins which play crucial roles in the urinary concentrating mechanism.
Amphibian Proteins↗