bluuebunny/crossref_metadata_2025 huggingface dataset:
Bicarbonate transport by amphibian nephron
Authors: Yucha C. B. , Stoner L. C.
Published: December 2017

To determine the site of bicarbonate reabsorption, tubular fragments from five different segments of the salamander nephron (Ambystoma) were perfused in vitro. Bicarbonate contents (total CO2) of tubular fluid were determined by microcalorimetry. Bicarbonate was not transported by the diluting segment or the mid-distal tubule. Although proximal tubule fragments did appear to reabsorb bicarbonate (10.8 +/- 3.7 pmol X mm-1 X min-1, P less than 0.01, n = 14), the chemical gradients observed were small with respect to the sensitivity of our methods. In the late distal tubule (LDT), bicarbonate reabsorption averaged 28.9 +/- 8.2 pmol X mm-1 X min-1 (P less than 0.01, n = 16). Transport in this segment was inhibited by ethoxzolamide or by perfusing with a sodium-free solution. Ethoxzolamide had no effect on the trans-epithelial voltage. Thus bicarbonate is reabsorbed by the LDT of amphibia via a mechanism that is dependent on carbonic anhydrase and the presence of luminal sodium. The 13 initial collecting tubules (ICT) studied did not appear to reabsorb bicarbonate. On the other hand, some ICT developed substantial bicarbonate gradients. Therefore this nephron segment has the capacity to reabsorb bicarbonate.
Contractile effects of TxA2 and endoperoxide analogues on cultured rat glomerular mesangial cells
Authors: Mene P. , Dunn M. J.
Published: December 2017

Vasoconstrictor metabolites of arachidonic acid (AA) affect renal hemodynamics in various disease models. Since mesangial contraction could be involved in the glomerular response to vasoconstrictors, we studied the effects of thromboxane A2 (TxA2), synthesized by sheep platelet microsomes, and of two stable prostaglandin (PG) endoperoxide analogues (END), U-44069 and U-46619, on the morphology of cultured rat mesangial cells. Computer-assisted image analysis microscopy was employed to measure cross-sectional area (CSA) of individual cells during 40-min incubations with the agonists. Both END induced a dose-dependent increase of contracting cells (U-44069, 1 pM, 14.2%; 1 nM, 25.0%; 1 microM, 34.4%; maximum CSA decrease, 16.6 +/- 2.9%; U-46619, 1 pM, 11.4%; 1 nM, 25.6%; 1 microM, 37.2%; maximum CSA decrease, 23.6 +/- 2.2%). TxA2 contracted 30.1% of the cells, with a maximum CSA decrease of 20.5 +/- 2.4%. The TxA2-receptor antagonists EP 092 (EP) and SQ 27,427 (SQ) significantly (P less than 0.05) reduced the number of cells contracting in response to U-44069 (+EP 7.3%, +SQ 10.8%) or U-46619 (+EP 14.2%, +SQ 11.1%), and eliminated TxA2-induced contraction. END also stimulated mesangial immunoreactive prostaglandin E2 (PGE2) synthesis (U-44069, 1 nM, from 2.17 +/- 0.62 to 4.36 +/- 1.0; U-46619, 1 nM, from 2.09 +/- 0.64 to 5.05 +/- 1.04, ng X mg protein-1 X 15 min-1 +/- SE). These results suggest that mesangial contraction, with resulting reduction of filtration surface area, may contribute to the effects of TxA2 and endoperoxides on glomerular hemodynamics.
Enhanced cAMP response to vasopressin in the CCT of DOCA-Na hypertensive rats
Authors: Pettinger W. A. , Fallet R. , Wang Y. , Tam L. T. , Jeffries W. B.
Published: December 2017

We characterized altered adenosine 3',5'-cyclic monophosphate (cAMP) regulation in deoxycorticosterone acetate (DOCA)-Na hypertensive rats using endogenous cAMP accumulation in the intact cell system of microdissected renal tubule fragments. Increased cAMP accumulation in response to vasopressin (VP) in cortical collecting tubules (CCT) began on day 5 (67%) after exposure to DOCA-Na and increased by 320% on day 42. Increased blood pressure began after day 7 and polyuria after day 17. The increased response to VP was DOCA dependent and appears to be exaggerated by dietary NaCl. Anatomic and hormone specificity studies were done on days 21-30. These included cAMP responses to prostaglandin E2, parathyroid hormone, thyrocalcitonin, VP, and isoproterenol in the CCT. The cAMP response to VP was measured in the glomerulus, proximal convoluted tubule, thin descending limb of Henle, medullary thick ascending limb of Henle, cortical thick ascending limb of Henle, medullary collecting tubule, and CCT. The supersensitivity occurred only to VP and only in the CCT. Thus this alteration in the VP response is anatomic and hormone specific and does not appear to be an acute effect of DOCA, since it was not present on day 1 and on day 3 of DOCA exposure. DOCA-Na hypertension is VP dependent. A specific exaggerated cAMP response to this hormone in the CCT would be expected to cause increased sodium retention. Whether increased sodium retention at this site contributes to hypertension in the DOCA-Na rat is unknown.
Reassembly of the occluding junctions in a renal cell line with characteristics of proximal tubular cells
Authors: Rabito C. A.
Published: December 2017

LLC-PK1 cells from trypsin-treated confluent cultures formed a continuous monolayer when plated at high cell density on collagen-coated Nuclepore filters. These monolayers developed a significant transepithelial electrical resistance that reached a maximum at 20 h. At 48 h, the resistance decreased to a value usually one-half the value obtained at 20 h. These changes were associated with an increase in the cell density of the monolayers. The drop in electrical resistance at 48 h was not observed when cell growth was arrested with excess thymidine. A hyperbolic relationship was demonstrated between cell density and electrical resistance. Although the increase in cell density was associated with an increase in the unidirectional flux of mannitol across the monolayers, selectivity studies indicated that the intrinsic properties of the occluding junctions were similar in the high and low cell density monolayers. These results indicate that, when cell growth is not arrested, changes in transepithelial electrical resistance observed after plating correspond to an increase in cell density and not to changes in the intrinsic properties of the occluding junctions. The development of transepithelial electrical resistance was delayed when the cells were in exponential growth. No such delay was observed, however, when exponential growth was synchronized. These findings and results obtained with the antimicrotubular agent Nocodazole indicate that the delay in the development of transepithelial electrical resistance is due to the asynchronous transit of the cells through the mitotic phase of the cell cycle: a time when most of the intercellular junctions are probably disrupted. Further investigation revealed that inhibition of protein but not mRNA synthesis blocked the development of occluding junctions in cells from confluent and exponentially growing cultures alike. These results indicate that, in contrast to MDCK cells, regulation of the occluding junctions in exponentially growing LLC-PK1 cells occurs at the translational not at the transcriptional level of protein synthesis.
Nitrogen sources for renal ammoniagenesis: study with 15N amino acid
Authors: Nissim I. , Yudkoff M. , Segal S.
Published: December 2017

The contribution of amino acids other than glutamine to renal ammoniagenesis was investigated in renal tubules obtained from control rats and rats with metabolic acidosis by incubating 2.5 mM [5-15N]glutamine, [2-15N]glutamine, [15N]glutamate, [15N]aspartate, [15N]alanine, or [15N]glycine, either as the sole N source in Krebs bicarbonate buffer or as a labeled substrate in a medium containing a mixture of unlabeled amino acids. With control tissue in Krebs buffer, approximately 75% of total ammonia was derived from 5-N of glutamine, whereas 2-N of glutamine, glutamate, aspartate, alanine, and glycine supplied 1, 10, 13, 4, and 18%, respectively. In the acidotic state, these values were 51, 30, 30, 30, 10, and 15% of the total ammonia produced, respectively. The ammonia that could not be accounted for by 15N analysis was derived from endogenous sources. Studies with tubules incubated in Krebs medium alone indicated that, in both control and acidosis, the calculated fraction of ammonia derived from endogenous sources was significantly decreased by addition of either 0.7 or 2.5 mM glutamine. However, ammonia production from endogenous sources was similar whether 0.7 or 2.5 mM glutamine was used as a sole exogenous substrate. Incubations of control tissue in buffer supplemented with an amino acid mixture revealed a significant decrease in ammonia production from [5-15N]glutamine compared with incubation in Krebs buffer alone. In chronic acidosis, no significant difference was found in total ammonia formation from [5-15N]glutamine compared with Krebs buffer alone.(ABSTRACT TRUNCATED AT 250 WORDS)
Chronic effects of vasopressin on fluid volume distribution in conscious dogs
Authors: Merrill D. C. , Cowley A. W.
Published: December 2017

Previous studies have suggested that acute elevations of arginine vasopressin (AVP) may result in an extravascular to intravascular shift of fluid independent of any change in total body H2O (TBW). The present studies examined the chronic influence of elevated AVP on fluid volume distribution in five splenectomized, sodium-deprived conscious dogs (avg body wt = 18.9 +/- 0.7 kg). During 4 days of continuous intravenous AVP infusion (0.36 ng X kg-1 X min-1), the computerized average 24-h total body weight was maintained within 110 g of the control value by means of a sensitive servo-controlled scale device. Urine flow and urine osmolality averaged 335 +/- 52 ml/day and 637 +/- 36 mosmol/kg during the preinfusion period and changed to levels averaging 151 +/- 14 and 1,377 +/- 121 with elevated AVP (P less than 0.05). Chromium-51-labeled red cell volume (51Cr RBC), plasma volume (Evans blue), TBW (3H2O), calculated total blood volume (using 51Cr RBC and Hct), and mean arterial pressure averaged 22 +/- 1 ml/kg, 54 +/- 7 ml/kg, 0.62 +/- 0.04 l/kg, 68 +/- 3 ml/kg, and 99 +/- 3 mmHg, respectively, during the control period and remained unchanged during the AVP infusion period. Plasma protein, sodium, and osmolality averaged 6.4 +/- 0.1 g/dl, 145.7 +/- 0.8 meq/l, and 295.0 +/- 1.5 mosmol/kg during the preinfusion period and also remained unchanged with elevated AVP. We conclude from the present studies that AVP has minimal or no chronic influence on internal volume redistribution.
Control of renal hemodynamics in hyperglycemia: possible role of tubuloglomerular feedback
Authors: Woods L. L. , Mizelle H. L. , Hall J. E.
Published: December 2017

The purpose of this study was to test the hypothesis that hyperglycemia, comparable with that found in uncontrolled diabetes mellitus, increases renal blood flow (RBF) and glomerular filtration rate (GFR) through a tubuloglomerular feedback (TGF) mechanism. We infused glucose intrarenally (0.1-0.3 g/min) into anesthetized dogs with normal kidneys (NK), with nonfiltering kidneys (NFK) in which changes in TGF were blocked, and with normal kidneys in which renal perfusion pressure (RAP) was lowered to the limits of renal autoregulation (LPK). Calculated intrarenal plasma glucose levels rose to 250-400 mg/dl. In NK (n = 6) RBF and GFR increased by 18 +/- 3 and 19 +/- 5%, respectively, and renal vascular resistance fell by 17 +/- 2% after 90 min. The renal hemodynamic responses to glucose were abolished in NFK (n = 8); RBF averaged 96 +/- 4% of control after 60 min of hyperglycemia. RBF and GFR did not change during hyperglycemia in LPK (n = 5), averaging 96 +/- 1 and 100 +/- 8% of control, respectively, after 60 min. Autoregulation of RBF and GFR during reductions in RAP was impaired during hyperglycemia in NK; RBF and GFR were effectively autoregulated between RAP of 126 and 70-85 mmHg during the control period, whereas during glucose infusion RBF and GFR fell by 31 +/- 9 and 47 +/- 10%, respectively, when RAP was reduced in steps to 70 mmHg. These data suggest that hyperglycemia impairs renal autoregulation and may increase renal blood flow and GFR through a tubuloglomerular feedback mechanism.
Renal alpha 2-adrenoceptors and the adenylate cyclase-cAMP system: biochemical and physiological interactions
Authors: Pettinger W. A. , Umemura S. , Smyth D. D. , Jeffries W. B.
Published: December 2017

alpha 2-Adrenoceptors were first described pharmacologically ten years ago. Within three years their capacity to inhibit adenylate cyclase had been demonstrated in many tissues. They were demonstrated biochemically in the kidneys in 1981 even before any renal physiological effects of their activation were known. They predominate numerically over alpha 1-adrenoceptors in renal membranes and their density is increased in genetic forms of rat hypertension. alpha 1-Adrenoceptors normally mediate the vasoconstriction and sodium- and water-retaining effects of sympathetic neuronally released norepinephrine. Norepinephrine or epinephrine must be infused to activate alpha 2-adrenoceptors, suggesting that renal alpha 2-adrenoceptors are extrajunctional, whereas alpha 1-adrenoceptors are postjunctional. When alpha 1-adrenoceptors are chronically blocked, renal alpha 2-adrenoceptor density increases and they assume a location at postjunctional sites, the otherwise exclusive domain of alpha 1-adrenoceptors. Results from microdissection studies have established that alpha 2-adrenoceptors are present on most segments of the nephron and that their activation can suppress adenosine 3,'5'-cyclic monophosphate (cAMP) accumulation induced by most renal hormones. However, failure of alpha 2-adrenoceptor activation to suppress cAMP accumulation in some tubular segments induced by certain hormones suggests compartmentalization of adenylate cyclase regulation that is hormone-function specific. In view of the potent inhibitory effects of alpha 2-adrenoceptor stimulation on hormone activated cAMP accumulation in several discrete areas of the nephron, we suggest that alpha 2-adrenoceptors fulfill important regulatory role(s) in renal function. To date, alpha 2-adrenoceptor activation has been shown to reverse vasopressin-induced sodium and water retention, and arachidonic acid- and furosemide-induced cAMP, sodium, and water excretion in the isolated perfused kidney. Thus the effects are qualitatively and quantitatively dependent in these studies on the hormone being infused and are therefore hormone-function specific. Physiological effects of alpha 2-adrenoceptor activation of thyrocalcitonin and on parathyroid hormone-induced effects have not been studied. alpha 2-Adrenoceptor activation can inhibit renin release in some model systems and can activate a sodium-hydrogen antiporter system in proximal tubules. The physiological roles of these actions are unknown.
Presence of multiple sodium-dependent phosphate transport processes in proximal brush-border membrane
Authors: Walker J. J. , Yan T. S. , Quamme G. A.
Published: December 2017

Renal brush-border membrane phosphate transport was studied in early and late segments of the pig proximal tubule. Vesicles were prepared from early proximal tubules (outer cortical tissue) and late proximal tubules (outer medullary tissue). Sodium-dependent phosphate uptake into brush-border membrane vesicles was determined using voltage clamp at 5-6 s, 21 degrees C. Sodium-dependent D-glucose uptake was determined to verify the cortical and medullary tissue cuts. At pH 8.0 (pHi = pHo), two sodium-dependent phosphate transport systems were evident in the early proximal tubule: a high-affinity system [Km, 0.06 +/- 0.01 mM; maximal transport activity (Vmax), 3.6 +/- 1.1 nmol X mg protein-1 X min-1] and a low-affinity system (Km, 4.11 +/- 0.02 mM; Vmax, 9.7 +/- 0.7 nmol X mg protein-1 X min-1). In the late proximal tubule at pH 8.0, only a single high-affinity transport process (Km, 0.19 +/- 0.7 mM; Vmax, 3.4 +/- 0.5 nmol X mg protein-1 X min-1) was evident. D-Glucose kinetics at pH 7.0 revealed both a high-affinity (Km, 0.55 +/- 0.09 mM) and a low-affinity (Km, 20.09 +/- 1.39 mM) system in the early proximal segment and a single high-affinity (Km, 1.27 +/- 0.36 mM) process in the late segment. These data suggest that two systems, distinct in their affinities and capacities, are involved in both D-glucose and phosphate transport across the brush-border membrane of the early proximal tubule, but that only a single high-affinity system is present in the late segment.
Increased release of norepinephrine and dopamine from canine kidney during bilateral carotid occlusion
Authors: Bradley T. , Hjemdahl P. , DiBona G. F.
Published: December 2017

The renal overflow of norepinephrine (NE) and dopamine (DA) to plasma from the innervated kidney was studied at rest and during sympathetic nervous system activation by bilateral carotid artery occlusion (BCO) in vagotomized dogs under barbiturate or barbiturate/nitrous oxide anesthesia. BCO elevated arterial pressure and the arterial plasma concentrations of NE, DA, and epinephrine (Epi). Renal vascular resistance (renal arterial pressure kept constant) increased by 15 +/- 7% (P less than 0.05) and the net renal venous outflows (renal venoarterial concentration difference X renal plasma flow) of NE and DA were enhanced (P less than 0.05). To obtain more correct estimates of the renal contribution to the renal venous catecholamine outflow, we corrected for the renal extraction of arterial catecholamines, assessed as the extractions of [3H]NE, [3H]DA, or endogenous Epi. The [3H]NE corrected renal NE overflow to plasma increased from 144 +/- 40 to 243 +/- 64 pmol X min-1 (P less than 0.05) during BCO, which, when compared with a previous study of the [3H]NE corrected renal NE overflow to plasma evoked by electrical renal nerve stimulation, "corresponds" to a 40% increase in nerve impulse frequency from approximately 0.6 Hz. If the renal catecholamine extraction was not taken into account the effect of BCO was underestimated. The renal DA overflow to plasma was about one-fifth of the NE overflow both at rest and during BCO, indicating that there was no preferential activation of noradrenergic or putative dopaminergic nerves by BCO.
Role of renal nerves in compensatory adaptation to chronic reductions in sodium intake
Authors: Mizelle H. L. , Hall J. E. , Woods L. L. , Montani J. P. , Dzielak D. J. , Pan Y. J.
Published: December 2017

The aim of this study was to investigate the importance of the renal nerves in adaptation to chronic reductions in sodium intake. Conscious dogs with unilateral (n = 7) or bilateral (n = 4) renal denervation were studied. In dogs studied before and after bilateral denervation, there were no differences in urine volume (UO), Na excretion (UNaV), or fractional reabsorption of Li (FR Li, an index of proximal tubular Na reabsorption) between innervated and denervated kidneys on either normal (80 meq/day) or low Na intake (5 meq/day, 15 days). Plasma renin activity (PRA) was attenuated following denervation on both normal (0.39 +/- 0.06 vs. 0.18 +/- 0.01 ng angiotensin I X ml-1 X h-1) and low Na intake (1.00 +/- 0.06 vs. 0.59 +/- 0.01). In unilaterally denervated dogs the left kidney was denervated and the bladder was split, allowing continuous urine collection from separate innervated and denervated kidneys in the same dog. There was no difference in UO between innervated and denervated kidneys on normal (80 meq/day) or low (7 meq/day, 9 days) Na intake. UNaV averaged 33.6 +/- 1.3 and 37.6 +/- 2.1 meq/day in innervated and denervated kidneys, respectively, on normal Na intake and 3.5 +/- 0.5 and 4.0 +/- 0.4 meq/day in innervated and denervated kidneys on low Na intake. FR Li was not different in denervated compared with innervated kidneys during normal or low sodium intake. Norepinephrine content was reduced by 99 +/- 1% in denervated kidneys.(ABSTRACT TRUNCATED AT 250 WORDS)
Effect of bicarbonate and phosphate on renal phosphate leak in experimental Fanconi syndrome
Authors: Shvil Y. , Wald H. , Popovtzer M. M.
Published: December 2017

The role of acidosis in the renal phosphate leak in Fanconi syndrome (FS) was studied in maleate-induced FS in rats. Clearance studies were performed in the following groups: 1) intact rats served as control, 2) rats with maleate-induced FS, 3) rats with FS receiving intravenous bicarbonate (HCO3-), 4) intact rats receiving intravenous 0.03 N HCl (inducing acidosis similar to that of Group 2), 5) rats with FS receiving intravenous phosphate buffer and NaCl, and 6) rats with FS receiving intravenous phosphate buffer and bicarbonate similar to Group 3. In Group 2 serum pH and fractional excretion of phosphate (CP/GFR) averaged 7.31 +/- 0.08 (mean +/- SE) and 1.00 +/- 0.06, respectively, and differed significantly from Group 1, in which the corresponding values were 7.41 +/- 0.01 and 0.12 +/- 0.02, respectively. In Group 3, intravenous HCO3- corrected pH to 7.43 +/- 0.01 and reduced CP/GFR to 0.33 +/- 0.05, both results were different from the corresponding rates in Group 2 (P less than 0.0005). In Group 4, intravenous HCl reduced serum pH to 7.31 +/- 0.02 (P not significant as compared with Group 2) and increased CP/GFR to 0.186 +/- 0.030, the latter was higher than CP/GFR in control rats (P less than 0.01) but was lower than that in HCO3- -treated FS rats. In Group 5 serum pH was 7.31 +/- 0.021, similar to Group 2. CP/GFR was 0.84 +/- 0.031, significantly lower than in Group 2 (P less than 0.05). In Group 6 serum pH was 7.43 +/- 0.013 and CP/GFR was 0.86 +/- 0.044.(ABSTRACT TRUNCATED AT 250 WORDS)
Interactions between ADH and prostaglandins in isolated erythrocyte-perfused rat kidney
Authors: Lieberthal W. , Vasilevsky M. L. , Valeri C. R. , Levinsky N. G.
Published: December 2017

Interactions between antidiuretic hormone (ADH) and renal prostaglandins in the regulation of sodium reabsorption and urinary concentrating ability were studied in isolated erythrocyte-perfused rat kidneys (IEPK). In this model, hemodynamic characteristics are comparable to those found in vivo, and tubular morphology is preserved throughout the period of perfusion. [Deamino]-D-arginine vasopressin (dDAVP) markedly reduced fractional sodium excretion (FE Na) in the IEPK from 3.5 +/- 0.6 to 0.45 +/- 0.14%. After indomethacin, FE Na fell still further to 0.08 +/- 0.02%. In the absence of dDAVP indomethacin had no effect on sodium excretion; FE Na was 2.4 +/- 0.6% in control and 2.0 +/- 0.4% in indomethacin-treated groups. dDAVP increased urine osmolality in the IEPK to 741 +/- 26 mosmol/kg. When prostaglandin synthesis was blocked with indomethacin, urinary osmolality increased further to 1,180 +/- 94 mosmol/kg. In isolated kidneys perfused without erythrocytes (IPK), dDAVP decreased FENa from 14.5 +/- 1.8% to 9.6 +/- 1.2%; addition of indomethacin had no further effect. dDAVP increased urine osmolality only modestly to 350 +/- 12 mosmol/kg in the IPK and indomethacin did not increase concentrating ability further (342 +/- 7 mosmol/kg). Thus the IEPK (unlike the IPK) can excrete a markedly hypertonic urine in response to ADH. ADH also enhances tubular reabsorption of sodium in the IEPK. Prostaglandins inhibit both these actions of ADH but do not directly affect sodium excretion in the absence of the hormone.
Intracellular messenger for action of angiotensin II on fluid transport in rabbit proximal tubule
Authors: Dominguez J. H. , Snowdowne K. W. , Freudenrich C. C. , Brown T. , Borle A. B.
Published: December 2017

These studies were designed to examine the cellular messenger that mediates the action of angiotensin II on fluid transport (Jv) in the rabbit proximal tubule. We measured the effects of angiotensin II on Jv, activation of adenylate cyclase, and the concentration of cytosolic free calcium (Cai) in the rabbit proximal tubule. In nine rabbit proximal convoluted tubules (PCT), angiotensin II, 10(-8) M and 10(-6) M, decreased Jv by 18 and 25%, P less than 0.05. In eleven rabbit proximal straight tubules (PST), 10(-8) and 10(-6) M angiotensin II decreased Jv by 20 and 23%, P less than 0.02. Angiotensin II did not affect lumen-to-bath phosphate fluxes in PCT or PST, and it did not activate adenylate cyclase in PST. In a preparation of proximal tubules (PCT and PST) loaded with aequorin, angiotensin II, 10(-8) and 10(-6) M, transiently increased Cai by 13 and 32%, P less than 0.001. We propose that Cai surges, activated by angiotensin II, are part of a cellular message that inhibits Jv in the rabbit proximal tubule.
Total CO2 absorption in the distal tubule of the rat
Authors: Kunau R. T. , Walker K. A.
Published: December 2017

By use of in vivo microperfusion methodology, we assessed proton secretion (acidification) in the superficial distal tubule of the rat by determining the rate of total CO2 (tCO2) absorption (JtCO2). In these studies, we compared the JtCO2 in rats fed a diet that increased urine pH to the JtCO2 in rats fed a high-protein diet that reduced urine pH. The effect of amiloride added to the perfusate, used in rats fed the high-protein diet, was also examined. In rats, Group 1, fed a commercial diet, urine pH was 6.9; plasma tCO2 was 30.0 mM, and JtCO2 was 15.5 +/- 5.3 pmol X mm-1 X min-1. Following the ingestion of a high-protein diet the night before study, the urine pH fell to 5.6 and the plasma tCO2 to 28.2 mM. The JtCO2 in this group, Group 2, 41.1 +/- 4.8 was significantly greater than Group 1, P less than 0.05. The late distal transepithelial potential difference was comparable in both groups, -50.3 +/- 4.3 vs. -45.2 +/- 3.1 mV, P not significant. In a third group, Group 3, amiloride (10(-4) M) was added to the perfusate of rats prepared as in Group 2. JtCO2 was 23.4 +/- 0.4 pmol X mm-1 X min-1, significantly less than Group 2, P less than 0.05. The transepithelial potential difference was reduced to -4.0 +/- 2.3 mV, P less than 0.01 vs. Group 2. We conclude that the superficial distal tubule of the rat responds to subtle stimuli to increase proton secretion and contributes to urinary acidification. The rate of acidification can be influenced by alterations in the electrical profile across the acidifying epithelium.
Influence of salt on response to nitrendipine by Dahl rat kidney
Authors: Steele T. H. , Challoner-Hue L.
Published: December 2017

We examined the responses to the calcium channel blocker, nitrendipine, of isolated perfused kidneys from Dahl salt-sensitive (DS) and salt-resistant (DR) rats that had been stabilized on high- and low-NaCl diets. Blood pressures of high-salt DS rats exceeded those of the other three groups. After norepinephrine vasoconstriction sufficient to increase renal vascular resistance (RVR) by 50%, the superimposition of 10(-5) M nitrendipine increased the glomerular filtration rate (GFR) of high-salt DS rat kidneys by 125% over control values but returned the GFR of high-salt DR kidneys only to control. Nitrendipine superimposition increased the GFR of low-salt DS and DR rat kidneys by 124 and 40% over control values, respectively, and partially restored the RVR toward control. Nitrendipine alone, without norepinephrine, did not affect the GFR or RVR. The persistence within the DS kidney of an exaggerated glomerular circulatory “rebound” response to nitrendipine following the development of hypertension suggests the possibility of a maladaptation of DS kidney cell calcium regulation. The DR kidney manifests a similar response during salt restriction, but this disappears on a high-NaCl diet.
Cimetidine transport in rabbit renal cortical brush-border membrane vesicles
Authors: McKinney T. D. , Kunnemann M. E.
Published: December 2017

Cimetidine is an organic cation and commonly prescribed drug that is eliminated primarily by proximal renal tubular secretion. The present studies evaluated cimetidine transport in rabbit renal cortical brush-border membrane vesicles (BBMV). [3H]Cimetidine uptake varied inversely with media osmolarity and was stimulated with uphill transport above equilibrium values (overshoot) produced by an initial proton gradient directed from the vesicle interior outwardly. Uphill transport occurred earlier and was of greater magnitude at 25 degrees C than at 5 degrees C. pH-stimulated [3H]cimetidine uptake was inhibited by excess nonradiolabeled cimetidine, quinidine, and procainamide but was affected little by probenecid. Tetraethylammonium inhibited cimetidine uptake in the presence and absence of an initial proton gradient, indicating that nonionic diffusion and simple diffusion cannot totally account for cimetidine transport in BBMV. The protonophore carbonyl cyanide trifluoromethoxyphenylhydrazone (FCCP) inhibited pH-stimulated cimetidine uptake but had no effect on uptake occurring in the absence of an initial pH gradient. Preloading BBMV with an excess of procainamide enhanced cimetidine uptake. However, in the presence of FCCP, the combination of FCCP and valinomycin, or nigericin the effect of preloading with procainamide was diminished, suggesting that the apparent countertransport of cimetidine produced by procainamide was indirect and due to generation of a transvesicular proton gradient. These results are consistent with the hypothesis that cimetidine is transported across BBMV by organic cation-proton exchange.
The early proximal tubule: a high-capacity delivery-responsive reabsorptive site
Authors: Maddox D. A. , Gennari F. J.
Published: December 2017

The proximal convoluted tubule is responsible for reclaiming almost all of the filtered bicarbonate, glucose, and amino acids, as well as 40% or more of the filtered sodium, fluid, chloride, and phosphate. Walker and co-workers demonstrated the importance of this nephron segment as a high-capacity transport site in the first mammalian micropuncture studies, and they suggested that the first portion of the proximal tubule played a particularly important role in the ability of the nephron to adapt to variations in filtered load. Since then, many studies using micropuncture and in vivo and in vitro microperfusion techniques have confirmed that the early proximal tubule has a higher transport capacity than the late proximal tubule for a number of solutes. Moreover, at least for bicarbonate, fluid, and chloride, the transport capacity is not static, but is in a dynamic state, adapting in response to changes in filtration. In this review we have focused on the high capacity and load dependence of early proximal bicarbonate and fluid reabsorption. In addition, we summarize the evidence for axial heterogeneity along the proximal convoluted tubule for transport of a variety of other solutes.
Endocytosis by cultured mesangial cells and associated changes in prostaglandin E2 synthesis
Authors: Singhal P. C. , Ding G. H. , DeCandido S. , Franki N. , Hays R. M. , Schlondorff D.
Published: December 2017

The mechanism of macromolecule uptake by cultured mesangial cells was studied by use of transmission electron microscopy. In parallel, we investigated the effect of macromolecular uptake on prostaglandin E2 (PGE2) formation. Cultured rat mesangial cells were studied in their third passage. As model molecules, we used colloidal gold particles (10 nm diameter) coated either with polyethylene glycol (PEG) or fresh serum (SCG). Mesangial cells were incubated from 1 to 60 min and up to 12 h with either PEG or SCG particles. Endocytosis of SCG significantly exceeded that of PEG particles. The mechanism involved binding to coated pits, followed by formation of coated vesicles (endosomes), and eventually delivery of particles to lysosomes. Pretreatment with cytochalasin B virtually prevented endocytosis of SCG particles, indicating active participation of the cytoskeleton. Determination of PGE2 production in parallel showed that SCG significantly stimulated PGE2 synthesis within minutes, whereas PEG-coated gold had no effect. When gold particles were coated with decomplemented serum instead of fresh serum, the stimulation of PGE2 was partially, but not completely, prevented, indicating that complement may be one, but not the only ligand responsible for enhanced PGE2 production. Stimulation of PGE2 synthesis by SCG was not dependent on actual endocytosis, as it was not altered by cytochalasin B pretreatment. Thus, surface ligand-receptor interaction may be sufficient to trigger PGE2 synthesis. The interaction between mesangial endocytosis and PGE2 production may be important for glomerular pathophysiology.
Renal response to atrial peptides is reduced in experimental nephrosis
Authors: Perico N. , Delaini F. , Lupini C. , Remuzzi G.
Published: December 2017

The aim of this study was to evaluate the renal response to atrial extracts (AE) and synthetic atrial natriuretic factor (ANF) in control rats and in rats with experimental nephrotic syndrome (NS). NS was obtained by a single intravenous injection of adriamycin (7.5 mg/kg). Bolus injection of AE from normal or NS rats resulted in marked increase of diuresis and natriuresis in bioassay control rats (AE from normal rats, urine flow rate, 14.87 +/- 2.94 to 186.18 +/- 55.86 microliters/min; Na excretion, 0.68 +/- 0.26 to 21.80 +/- 5.45 mu eq/min; AE from NS, urine flow rate, 13.49 +/- 4.30 to 167.14 +/- 51.44 microliters/min; Na excretion, 0.98 +/- 0.57 to 20.71 +/- 9.76 mu eq/min). In contrast, blunted diuretic (from 11.26 +/- 3.05 to 65.20 +/- 27.30 microliters/min) and natriuretic (from 0.58 +/- 0.15 to 4.52 +/- 1.59 mu eq/min) effect was observed when AE were injected in rats with NS. Injection of the vehicle in which AE were dissolved or ventricular extracts did not increase urinary flow rate or Na excretion in both control and NS animals. Bolus injection of synthetic ANF (Arg-101-Tyr-126) induced marked diuretic and natriuretic response in control but not in NS rats. Similar results were obtained when AE were infused by constant infusion in control or in NS bioassay rats. AE given by constant infusion induced comparable increase in glomerular filtration rate (GFR) over basal values both in control and NS animals (controls, 39%; NS rats, 40%).(ABSTRACT TRUNCATED AT 250 WORDS)
Electroneutral H+ secretion in distal tubule of Amphiuma
Authors: Stanton B. , Omerovic A. , Koeppen B. , Giebisch G.
Published: December 2017

This study examines the cellular mechanisms of acid secretion by the in vitro perfused late distal tubule of Amphiuma kidney. Acidification of tubule fluid occurred against an electrochemical gradient of 16 mV; thus H+ secretion was active. Amiloride (1 mM) or a reduction of sodium in the perfusion fluid (from 83.7 to 7.7 mM) partially reduced acidification. Amiloride, in the presence of low sodium, completely inhibited acidification. Furthermore, acetazolamide and ouabain in the bath solution (0.1 mM) also inhibited acidification. Conductive properties of the epithelium and of individual cell membranes were determined by means of cable analysis of the tubule and intracellular voltage recordings. The transepithelial voltage and resistance averaged -0.4 +/- 0.4 mV, lumen negative, and 7,147 +/- 845 omega X cm, respectively. Two functionally different cell types were identified by intracellular microelectrodes. Type I cells had a basolateral membrane voltage (Vbl) of -67.7 mV. As determined by ion substitution experiments, the basolateral membrane was conductive to K+ and Cl-. This cell also had a 4-acetamido-4'-isothiocyanostilbene-2-2'-disulfonic acid (SITS)-sensitive Na+-dependent HCO3- exit pathway in the basolateral membrane. Type II cells had a Vbl of -76.1 mV (P less than 0.05 vs. type I) and the basolateral membrane was conductive to K+ and Cl- but not to HCO3-. HCO3- movement across the basolateral membrane in this cell may occur by electroneutral Cl- -HCO3- exchange. The apical cell membrane of both cell types did not contain measurable ionic conductances, as evidenced by a high value of apical membrane fractional resistance (0.98 +/- 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)
Biphasic effect of oxygen radicals on prostaglandin production by rat mesangial cells
Authors: Adler S. , Stahl R. A. , Baker P. J. , Chen Y. P. , Pritzl P. M. , Couser W. G.
Published: December 2017

Cultured rat mesangial cells were exposed to a reactive oxygen species (ROS) generating system (xanthine plus xanthine oxidase) to explore the effect of ROS on their metabolism of arachidonic acid (AA). Cell viability, as assessed by 51Cr release, was not affected by the concentrations of xanthine plus xanthine oxidase used. Prostaglandin E2 (PGE2) production following exposure to increasing quantities of xanthine plus xanthine oxidase was significantly decreased to 38.1 +/- 9.7 or 30.8 +/- 6.9% of control levels (P less than 0.05) when cells were stimulated with the calcium ionophore A23187 (1 microgram/ml) or AA (10(-6) M), respectively. Maximum suppression of production was seen within 10 min of ROS exposure. Thromboxane B2 production was similarly decreased to 83.1 +/- 7.6 (0.05 less than P less than 0.10) or 54.9 +/- 2.5% (P less than 0.05). This effect was reversed by addition of catalase to the ROS generating system but not by superoxide dismutase or mannitol, which suggested that H2O2 was the responsible metabolite. High levels of H2O2 (5 x 10(-4) M) suppressed PGE2 production to 44.0 +/- 4.1 or 17.4 +/- 6.2% of A23187- or AA-stimulated production (P less than 0.05). Lower levels of H2O2 resulted in significant stimulation of base-line PGE2 production. Analysis of release of [3H]AA-labeled metabolites from A23187-stimulated cells showed no effect of H2O2 on phospholipase activity. Thus ROS can stimulate or inhibit AA metabolism in the glomerular mesangium, which may have important effects on glomerular hemodynamics during glomerular injury.
Renal folate absorption and the kidney folate binding protein. I. Urinary clearance studies
Authors: Selhub J. , Emmanouel D. , Stavropoulos T. , Arnold R.
Published: December 2017

The kidney possesses a high concentration of a folate binding protein (FBP) that resides primarily in the brush-border membrane (BBM) of the proximal tubular cells. To assess the possible involvement of this protein in renal conservation of folate we determined the urinary clearance, in rats, of three forms of folates with sharply different affinities for FBP. After single intravenous injections of 0.1 to 1.0-nmol doses of radioactive folates the urinary clearance based on radioisotope determination was in the sequence: folic acid less than 5-methyltetrahydrofolate (5-CH3 THF) much less than methotrexate. At higher doses the urinary folate clearance was increased and the differences between the three injected forms were narrowed and were no longer noticeable at 100-nmol doses. Under conditions of continuous infusion to attain plasma folate levels of 2.3-5.7 pmol/ml, the urinary clearance based on chromatographic analyses of plasma and urine after correction for plasma folate binding was 0.20 ml/min for folic acid, 0.37 ml/min for 5-CH3 THF, and 1.76 ml/min for methotrexate. These chromatographic analyses have also shown the presence in both plasma and urine of metabolites formed from infused folates. Metabolites found after infusion of folic acid include 5-CH3 THF with a urinary clearance of 0.3 ml/min and an unknown with a urinary clearance of 0.8 ml/min. The latter metabolite appears also to occur in plasma and urine after infusion of 5-CH3 THF. Infusion of methotrexate was associated with the appearance of a metabolite with a urinary clearance of 2.5 ml/min. This sequence of urinary clearance is in inverse order to the affinities of these three forms of folate for the kidney BBM FBP.(ABSTRACT TRUNCATED AT 250 WORDS)
Prostaglandin independence of kinin-stimulated renin release
Authors: Beierwaltes W. H.
Published: December 2017

Bradykinin can increase prostaglandin synthesis and also stimulate renin release in vitro. Because prostaglandins also stimulate renin, studies were performed to determine whether bradykinin stimulation of renin is a function of prostaglandin synthesis. Isolated glomeruli with attendant arteriolar attachments were harvested from rat kidneys and superfused. The effluent was analyzed for renin, prostaglandins E2 and I2 (6-keto-PGF1 alpha). Bradykinin (10(-5) M) increased renin by 50% with a concomitant increase in prostacyclin (PGI2) but not in prostaglandin E2 (PGE2). The cyclooxygenase inhibitor meclofenamate (1.6 X 10(-5) M) inhibited bradykinin-induced PGI2 synthesis but not the concurrent increase in renin release. Additionally, neither the phospholipase inhibitor quinacrine (10(-2) M) nor the prostacyclin synthetase inhibitor 9,11-azoprosta-5,13-dienoic acid (Azo analogue-1) (5.67 X 10(-6) M) eliminated bradykinin-induced renin release. Superfusion with calcium-free media and EDTA increased basal renin release 2.5-fold, and bradykinin stimulated a twofold increase in renin release. Neither a high (10(-2) M) media calcium nor the calcium channel blocker nifedipine (10(-6) M) eliminated bradykinin stimulation of renin. These results suggest that bradykinin stimulation of renin is at least partially independent of prostaglandin synthesis and that bradykinin must act by some prostaglandin-independent pathway to induce renin release from isolated glomeruli.
Regulatory volume decrease in perfused proximal nephron: evidence for a dumping of cell K+
Authors: Kirk K. L. , DiBona D. R. , Schafer J. A.
Published: December 2017

We utilized the microscopic and morphometric procedures described in the preceding paper to examine the role of a swelling-activated dumping of K-salt in the reversal of hyposmotic cell swelling in the perfused proximal nephron. The rate of the regulatory volume decrease that follows cell swelling in dilute solutions was reduced by two maneuvers that attenuate the K+ chemical potential difference across the basolateral membrane; inhibiting the Na+-K+ pump (e.g., with ouabain) and raising the peritubular K+ concentration. The rate of the regulatory volume decrease was also inhibited by peritubular quinine, which blocks K channels and volume regulation for a number of mammalian cells. Additionally, exposure to hyposmotic solutions resulted in a sustained and quinine-sensitive increase in the apparent permeability of the basolateral membrane to K+ salt, which was monitored qualitatively as the rate of cell volume change that was induced by a perturbation in the peritubular K+ concentration. The simplest interpretation of these results is that the reversal of hyposmotic cell swelling in the proximal nephron is referable at least in part to a swelling-activated loss of K-salt and water from the cells.
Phorbol esters inhibit ammoniagenesis and gluconeogenesis in proximal tubular segments
Authors: Chobanian M. C. , Hammerman M. R.
Published: December 2017

To characterize the regulation of ammoniagenesis and gluconeogenesis in renal proximal tubule, ammonia and glucose productions were measured in suspensions of canine proximal tubular segments incubated with 10 mM L-glutamine. Productions were linear functions of time for 120 min and were decreased as extracellular pH was increased from 7.0 to 7.5 To ascertain whether activation of protein kinase c affects either process, we incubated segments with tumor-promoting phorbol esters, 12-O-tetradecanoylphorbol-13-acetate (TPA), or phorbol 12,13-dibutyrate, or with the inactive phorbol ester 4 alpha-phorbol. Ammoniagenesis and gluconeogenesis were inhibited by incubation with 10(-6) M of the two former compounds but not the latter compound. Inhibition of ammoniagenesis and gluconeogenesis occurred after incubation with as little as 10(-9) M phorbol 12,13-dibutyrate. Phorbol ester-induced inhibition was observed under conditions such that extracellular [Na+] was greater than intracellular [Na+], but not when extracellular [Na+] equaled intracellular [Na+], and was not observed in the presence of amiloride. Our findings are consistent with a role for protein kinase c in the control of ammoniagenesis and gluconeogenesis in proximal tubule. Such control could be mediated via stimulation of Na+-H+ exchange.
Mechanisms of lithium-vasopressin interaction in rabbit cortical collecting tubule
Authors: Cogan E. , Svoboda M. , Abramow M.
Published: December 2017

In single cortical collecting tubules (CCT) of the rabbit, guanosine 5'-triphosphate (GTP) increased the arginine vasopressin (AVP)-stimulated adenylate cyclase (AC) by 60% (P less than 0.05). In contrast, guanosine 5' O-(2-thio)-diphosphate (GDP-beta S), a competitive inhibitor of GTP action on the stimulatory guanine regulatory protein (Ns), reduced the AVP-stimulated AC activity by 72% (P less than 0.001), indicating the presence of endogenous GTP in the cells under study. That inhibitory effect was reversed by the addition of GTP to the incubation medium. In isolated perfused CCT, cholera toxin (CT) induced a significant increase in water permeability in the absence of AVP. In contrast, Bordetella pertussis toxin (BPT) did not modify the low AVP-independent water permeability. Lithium, an inhibitor of the hydrosmotic action of AVP, also inhibits the hydrosmotic action of CT by 70% (P less than 0.05) but not that of forskolin. The conclusions of the present study are Ns is required for AVP stimulation of AC in the CCT; Ns is functionally active in this system as evidenced by the hydrosmotic effect of CT; the lack of effect of BPT suggests that the low AVP-independent water permeability in the CCT is not the result of a tonic inhibition of the AC operating through the inhibitory guanine nucleotide regulatory protein; and the inhibition by lithium of the hydrosmotic action of AVP in the CCT appears to involve an interaction with the regulatory proteins (probably Ns) or with their binding to the catalytic unit of AC.
Isolated perfused Ambystoma proximal tubule: hydrodynamics modulates ultrastructure
Authors: Tripathi S. , Boulpaep E. L. , Maunsbach A. B.
Published: December 2017

A method using a pressure-sensing servo-pipette is described for measuring downstream transepithelial pressure within isolated renal tubules perfused at flow rates designed to keep luminal solution composition constant. The hydrodynamics of in vitro microperfusion of isolated proximal tubules of Ambystoma tigrinum was varied and different states of transepithelial hydrostatic pressure difference, axial tubule flow, and transepithelial transport were correlated with epithelial ultrastructure. Tubules analyzed by ultrastructural morphometry were as follows: unperfused with and without ouabain, perfused single-end cannulated with and without ouabain, and perfused double-end cannulated tubules incubated in substrate Ringer. The results indicate that proximal tubule fine structure is well preserved for more than 3 h in unperfused and perfused tubules. Small transepithelial hydrostatic pressure gradients (less than 162 Pa) increase tubule diameters and decrease cell height without changing volumes of the cells, lateral intercellular spaces (LIS), or the basal extracellular labyrinth (BEL). Pressure gradients of 271 Pa have no further effect on tubule diameters or cell height, but significantly reduce volumes of LIS and BEL. Transport inhibition and axial flow changes have minor structural effects. This study demonstrates a close dependence of tubule ultrastructure on hydrodynamic conditions and provides guidelines for optimizing the latter during perfusion of isolated renal tubules.