Identification and disruption of an Arabidopsis zinc finger gene controlling seed germination

We describe here the Arabidopsis gene DAG1, encoding a zinc finger transcription factor of the Dof family, and show that it is involved in the control of seed germination. By a reverse genetics approach, we isolated an Arabidopsis mutant line with one T-DNA insertion in DAG1. Seeds from homozygous knockoutdag1-1 plants do not develop dormancy and germinate also in the absence of light. Segregation analysis indicates that the effect of the mutation is maternal. Accordingly, in situ mRNA hybridizations reveal expression of DAG1 in the vascular tissue of the flower and maturing fruit but not in the seed.

Identification and disruption of an Arabidopsis zinc finger gene controlling seed germination

We describe here the Arabidopsis gene DAG1, encoding a zinc finger transcription factor of the Dof family, and show that it is involved in the control of seed germination. By a reverse genetics approach, we isolated an Arabidopsis mutant line with one T-DNA insertion in DAG1. Seeds from homozygous knockout dag1-1 plants do not develop dormancy and germinate also in the absence of light. Segregation analysis indicates that the effect of the mutation is maternal. Accordingly, in situ mRNA hybridizations reveal expression of DAG1 in the vascular tissue of the flower and maturing fruit but not in the seed.

An auxin-dependent distal organizer of pattern and polarity in the Arabidopsis root

Root formation in plants involves the continuous interpretation of positional cues. Physiological studies have linked root formation to auxins. An auxin response element displays a maximum in the Arabidopsis root and we investigate its developmental significance. Auxin response mutants reduce the maximum or its perception, and interfere with distal root patterning. Polar auxin transport mutants affect its localization and distal pattern. Polar auxin transport inhibitors cause dramatic relocalization of the maximum, and associated changes in pattern and polarity. Auxin application and laser ablations correlate root pattern with a maximum adjacent to the vascular bundle. Our data indicate that an auxin maximum at a vascular boundary establishes a distal organizer in the root.

Studies on 6-aminoquinolones: synthesis and antibacterial evaluation of 6-amino-8-ethyl- and 6-amino-8-methoxyquinolones

From our quantitative structure-activity relationship (QSAR) study on a large set of 6-aminoquinolones, which indicated that a group larger than methyl could be allocated at C-8 position, we have synthesized two new series of 6-aminoquinolones characterized by the presence of an ethyl or a methoxy group at C-8 position. The antibacterial evaluation shows that, while the 8-ethyl derivatives were devoid of any antibacterial activity, the introduction of methoxy group gave compounds with good antibacterial activity, especially against gram-positive bacteria. A tentative explanation of the different behaviours among the 8-substituted analogues is given taking into account both the length and electronic properties of the C-8 groups.

Age-related changes in renal function, membrane protein metabolism, and Na,K-ATPase activity and abundance in hypokalemic F344 x BNF(1) rats

BACKGROUND

Potassium depletion is a common electrolyte abnormality in elderly humans, usually as a consequence of diuretic use or poor oral intake. Hypokalemia is associated with a number of changes in renal function and an increase in some renal membrane transporters; its growth-promoting effect in young animals is well known. With aging, the renal adaptation to a number of challenges is often diminished. We hypothesized that aging is related to decreases in renal function, renal membrane protein metabolism, as well as Na, K-ATPase protein abundance and activity in both control animals as well as in those with potassium depletion.

OBJECTIVE

We examined the effects of dietary-induced hypokalemia in true-aged nonobese rats (30 months old) on renal function, cortical brush border membrane (BBM) and basolateral membrane (BLM) protein metabolism, and Na,K-ATPase protein abundance and activity. We compared the results obtained to those seen in their 4-month-old counterparts similarly treated.

METHODS

Young (4-month-old) and senescent (30-month-old) male Fisher 344 x Brown-Norway F(1) rats (F344 x BNF(1)) were fed either a normal or potassium-deficient diet for 7 days. At 24 h, the U-(14)C-leucine incorporation was measured for determination of protein metabolism in renal BBM and BLM. Cortical BLM vesicle and microdissected proximal convoluted tubule (PCT) Na, K-ATPase activities were determined along with Western blot analysis of the cortical BLM alpha(1) subunit of Na,K-ATPase. Metabolic and renal function parameters were also examined.

RESULTS

Hypokalemia caused hyperbicarbonatemia, hyperglycemia, and azotemia, but only in the senescent animals. The aged control rats had a higher basal level of urine volume, ammonium excretion, and fractional excretion of chloride. By contrast, aging in the F344 x BNF(1) rats was associated with a decrease in plasma aldosterone (by 35%) and phosphate (by 40%) levels as compared with their young controls. Hypokalemia resulted in a significant reduction of plasma aldosterone and a rise in muscle sodium concentration in both age groups; it significantly increased renal BBM and BLM protein concentrations in the young group, while these parameters remained unchanged in the senescent rats. The aged potassium-depleted animals showed a 14% decrease in BBM protein biosynthesis, but there were no changes in the young hypokalemic rats. Both potassium-depleted elderly and young rats had a significant reduction (by 33%) in BLM protein biosynthesis. Hypokalemia significantly increased the Na, K-ATPase activity in both cortical BLM vesicles and in microdissected PCT. The percentage increase in microdissected PCT segments (Na,K-ATPase activity) in elderly potassium-depleted animals was significantly less than that seen in hypokalemic young ones. Aging, per se, was associated with decreased basal microdissected PCT Na,K-ATPase activity in control animals. Hypokalemia had no effect on cortical BLM alpha(1) subunit Na, K-ATPase protein abundance in either age group.

CONCLUSIONS

The present study provides the first evidence in nonobese aged rats as to the metabolic parameters, renal function, renal cortical membrane protein metabolism, and transporter Na,K-ATPase activity and abundance during potassium depletion. The aged nonobese F344 x BNF(1) rats responded differently from their young nonobese counterparts following potassium depletion. These differences may contribute substantially to the effects often encountered in elderly humans receiving diuretics or having a poor dietary potassium intake.

Food restriction beneficially affects renal transport and cortical membrane lipid content in rats

Food restriction (FR) exerts a variety of beneficial effects and may prolong life in both humans and animals. However, studies of its effects on the cortical brush border membrane (BBM) and basolateral membrane (BLM) lipid concentration, which may be pertinent to renal function, have not been reported in detail. We hypothesized that FR would decrease renal work and lower renal membrane lipid concentration. The changes in lipid concentration would be most dramatic in BBM because this membrane is the entry site for the recovery of filtered ions and nutrients. Young male Fischer 344 x Brown-Norway F1 rats consumed food ad libitum (AL) or were food-restricted (FR, 60% of AL consumption) for 6 wk. AL rats had higher fractional excretions of Na(+), K(+), and Cl(-) than did the FR group (P < 0.001). Renal Na,K-ATPase activity in AL rats was 100% higher than in FR rats (P < 0.001), reflecting greater renal work. The work required for renal proton secretion was lower in FR than in the AL rats. In FR rats, all BBM phospholipid concentrations (phosphatidylserine, phosphatidylcholine, phosphatidylethanolamine, and sphingomyelin) were approximately 50% lower than in the AL rats (P < 0.001). In the BLM, food restriction resulted only in lower phosphatidylcholine concentration, while the other phospholipids were unaffected. Plasma and renal membrane (BBM and BLM) cholesterol concentrations were significantly lower in FR than in AL rats. These results show that a nutritionally complete, but energy restricted, diet improves renal function. It also prevents renal membrane lipid deposition and decreases plasma cholesterol. Prolonged food restriction might attenuate the renal injury that occurs in obese humans as a consequence of insulin resistance and atherosclerosis.

Potassium depletion: renal membrane lipid metabolism and Na/H exchanger abundance in aged F344 x BNF1 rats

Potassium depletion (-K) is a common electrolyte abnormality in elderly humans, occurring after diuretic use or poor oral intake. We hypothesized that aging would result in an increase in renal membrane lipid metabolism in both control and -K, and that the Na/H exchanger's protein abundance to -K would be blunted. Young and senescent non-obese male Fisher 344 x Brown-Norway F1 rats (F344 x BNF1) were fed either a normal or a K-deficient diet for 7 days. At 24-h, 32P incorporation was measured for renal cortical brush-border (BBM) and basolateral membrane (BLM) lipid metabolism. All -K animals showed a reduction in total body potassium stores, a fall in plasma aldosterone, a urinary concentrating defect, and an increase in plasma cholesterol and urine ammonium excretion (p < .001). In BBM of both age groups, -K increased phosphatidylserine, sphingomyelin, phosphatidylcholine, and phosphatidylethanolamine concentrations, but 32P incorporation fell. In BLM of young K-depleted rats, however, only phosphatidylcholine concentration increased. In the hypokalemic aged rats, the concentration of all BLM phospholipids rose, whereas 32P incorporation fell. In both membranes, cholesterol concentration and the molar ratio of cholesterol to total phospholipid increased with -K (p < .05). Potassium depletion caused brush-border membrane NHE-3 protein abundance to rise, but only in the young rats. Neither NHE-3 nor basolateral NHE-1 protein abundance was affected in aged animals with -K. These results provide the first evidence, in non-obese aged rats, that selective age-associated modifications occur in membrane lipid metabolism and membrane transporter protein abundance during -K. That aging causes a maladaptive response in brush-border NHE-3 protein expression may have important implications for elderly humans, particularly if they are given diuretics and become potassium depleted.

Role of calcium in the reaction between pyrroloquinoline quinone and pyridine nucleotides monomers and dimers

Redox reactions were carried out in aerobiosis and anaerobiosis between NAD(P) dimers or NAD(P)H and pyrroloquinoline quinone (PQQ) in different buffers. The buffer system and pH significantly affected the oxidation rates of nucleotides and the ESR signal intensity of the PQQ(*) radical formed in anaerobiosis by comproportion between the quinone and quinol forms. The relative reactivity of the four nucleotides toward PQQ was affected by pH and buffer nature. PQQ, which behaves as an electron shuttle from nucleotides to oxygen, was first converted to PQQH(2) and then rapidly reoxidized by oxygen, with formation of hydrogen peroxide. Both NAD(P) dimers and NAD(P)H consumed 1 mol of oxygen per mole of reacted molecule of pyridine nucleotide, yielding 1 or 2 mol of NAD(P)(+) from NAD(P)H or from NAD(P) dimers, respectively. Chelating agents such as EDTA and phytate strongly decreased the reaction rate and the PQQ(*) radical signal intensity. Kinetics carried out in the presence of metal ions showed instead an increased reaction rate in the order Ca(2+) >> Mg(2+) > Na(+) >> K(+). Spectrofluorimetric measurements of PQQ with increasing concentrations of Ca(2+) showed a fluorescence quenching and shift of the maximum emission toward lower wavelengths, while other metal ions showed minor effects, if any. Therefore, it is demonstrated that Ca(2+) binds to PQQ, probably forming a complex which is more reactive with both one-electron (NAD(P) dimers) or two-electron donors (NAD(P)H) in nonenzymic reactions. It is important to recall that Ca(2+) was already found to play active role in PQQ-containing enzymes.

Altered sodium pump alpha and gamma subunit gene expression in nephron segments from hypertensive rats

OBJECTIVE

To determine the qualitative and quantitative expression of alpha and gamma sodium pump subunits in whole kidney and nephron segment RNA from Sprague Dawley rats, spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats.

DESIGN

A novel reverse transcription polymerase chain reaction technique was devised which provides accurate and precise measurement of the number of molecules of specific transcript abundance, a measurement of gene expression. This allows the quantitative comparison of multiple samples across multiple subjects and, since the estimates are accurate rather than relative, can also be used to make quantitative comparisons across expressed genes, such as isoforms and subunits of the heterotrimeric renal sodium pump.

METHODS

We examined which catalytic isoforms were expressed and then quantified transcript abundance in whole kidney and convoluted and straight segments of the proximal tubule.

RESULTS

Alpha 1 and gamma transcripts, but not alpha 2, alpha 3 or alpha 4 isoforms, were consistently observed in nephron segments. Levels of alpha 1 were lower in kidney RNA from 15-16-week-old SHR than in WKY rats of the same age (P = 0.001), but were not different between SHR and WKY in 4-5-week-old animals. No significant difference was observed in gamma subunit abundance in kidney RNA from 4-5-week-old animals; however, at 15-16 weeks, the expression in SHR was one-third that in WKY rats (P = 0.003). In proximal convoluted tubules from 4-5-week-old animals, the level of alpha 1 RNA expression was lower (P = 0.03) in SHR than in WKY rats. In addition, levels of alpha 1 in proximal straight tubule from the 4-5-week-old SHR were also lower than in WKY rats (P = 0.02). This difference was even greater in 15-16-week-old animals: in SHR, alpha 1 expression was less than 20% of the level of expression in WKY rats (P = 0.0003). Expression of the gamma subunit exhibited a similar pattern of downregulation in SHR. In RNA from proximal convoluted tubules and proximal straight tubules from both 4-5- and 15-16-week-old animals, expression of the gamma subunit was demonstrated to be significantly lower in SHR than in WKY rats.

CONCLUSION

The results indicate a coordinate reduction in the abundance of sodium pump alpha and gamma subunits in the proximal tubules of SHR, which occurs early during the development of hypertension.

Design and synthesis of modified quinolones as antitumoral acridones

The bacterial topoisomerase II (DNA gyrase) and the mammalian topoisomerase II represent the cellular targets for quinolone antibacterials and a wide variety of anticancer drugs, respectively. In view of the mechanistic similarities and sequence homologies exhibited by the two enzymes, tentative efforts to selectively shift from an antibacterial to an antitumoral activity was made by synthesizing a series of modified tricyclic quinolones, in which the essential 3-carboxylic function is surrogated by phenolic OH and the classic C-6 fluorine atom is replaced by a NH2 group. The resulting 7-amino-9-acridone derivatives were assayed for their antibacterial as well as cytotoxic activities. No antibacterial activity was found. On the other hand, many derivatives showed significant cytotoxic activity against both HL-60 and P388 leukemias and a wide panel of human and rodent solid tumor cells, derivatives 25 and 26 displaying the best overall antiproliferative activity. Against the LoVo cell line, derivative 25 exhibited higher cytotoxic effects than etoposide.

Experimental studies in distal urinary acidification: bringing the bedside to the bench

The renal tubular acidosis syndromes are nonuremic defects of urinary acidification. They are characterized by a normal anion gap and hyperchloremic metabolic acidosis; plasma potassium may be normal, low, or high, depending on the syndrome present. As new technologies have been applied to biology, we now better understand the basic lesions of these important syndromes.

Drug substitution in transplantation: a National Kidney Foundation White Paper

Specific safeguards to guide the approval process and substitution practices for generic immunosuppressive agents are necessary for the effective delivery of patient care. Currently, the Food and Drug Administration (FDA) requires the demonstration of bioequivalence of generic drugs to innovator drugs in normal healthy subjects, a criterion that may be insufficient for critical-dose drugs. For generic equivalents of critical-dose drugs and for innovator critical-dose drugs, there should be a requirement for replicate studies measuring intrasubject variability and subject-treatment interactions to establish that bioequivalence holds true. Extensive testing of generic drugs in all target patient types is impractical and should not be required. However, when evidence suggests that the bioavailability of a critical-dose drug may vary substantially in certain subgroups, the FDA should require a demonstration of bioequivalence of generic versions to innovator products in these representative target populations. Changes in the approval process for generics should be accompanied by more consistent substitution practices. Pharmacists should notify the prescribing physician and patient whenever a critical-dose drug (generic or brand name) is dispensed in a different formulation from the one the patient has been taking. Therapeutic substitution for such drugs should not be made unless the prescribing physician has granted approval. The health care provider should consider instituting appropriate monitoring whenever patients are switched between generic formulations or between innovator drugs and generic formulations. Patients should be well informed about generic substitutes so that they can participate in treatment choices.

Anemia and cardiovascular complications: iron and EPO impact

Management of end-stage renal disease (ESRD) has been revolutionized by the advent of erythropoietin replacement. We briefly review its characteristics and clinical use. Also emphasized is the importance of iron deficiency in limiting the clinical response to erythropoietin therapy. Iron-replacement therapy in ESRD patients is briefly discussed.

Encephalopathy, hearing loss and retinal occlusions (Susac's syndrome): a new case

We describe a young woman with retinal arteriolar occlusions, encephalopathy, and hearing loss. At present this disorder is known as Susac's syndrome, a microangiopathy of the brain and retina whose pathogenesis is, however, unknown. The article reviews the clinical features of this rare, but not unusual, syndrome that can easily be misdiagnosed as multiple sclerosis.

Renal Na+, K+-ATPase in SHR: studies of activity and gene expression

The mechanism by which increased dietary intake of calcium reduces blood pressure in the spontaneously hypertensive rat is unknown. The present studies were designed to determine if there were alterations in the activity of the major membrane ion translocating pump, sodium, potassium-ATPase (NKA), in the kidneys of hypertensive rats and whether increased dietary calcium intake affected the activity of this enzyme. Fifteen-week old SHR's were found to have lower total ATPase activity in microsomal preparations from the kidney than age matched Wistar-Kyoto animals. Both the ouabain-sensitive component (NKA) and the ouabain-insensitive component were lower in SHR. Increasing dietary calcium intake from 1% to 3% elevated both components of the ATPase activity in SHR, but was without effect in WKY. Measurement of membrane phospholipid composition suggested that altered phospholipid composition did not account for the reduced ATPase activity observed, but indicated a reduced density of ATPase in SHR. A technique has been devised for qualitative and quantitative analysis of Na, K-ATPase alpha isoforms using RT-PCR. This technique reveals that the alpha 1 isoform is the sole catalytic isoform present in the nephron. Accurate and precise quantification of the amount of gene expression in individual nephron segments is reported and will be applied to determine whether dietary calcium influences blood pressure by a mechanism which alters nephron NKA gene expression.

Modeling and analysis of competitive RT-PCR

The present studies demonstrate a theoretical and practical framework for the accurate quantitation of gene expression in RNA extracted from microscopic tissue samples. The approaches are developed around competitive RT-PCR techniques. Assay performance has been examined and validated at both the RT and PCR steps. Our analysis of RT transcription efficiency for a number of native and competitor combinations shows that this property can differ, even for very similar templates. However, this difference is consistent and, once identified and measured, can be removed as an obstacle to accuracy. Using mathematical modeling, we have examined the simulated co-amplification of native and competitor templates in PCR. Useful insights have emerged from such modeling which indicate that differences in initial amplification efficiency and the rate of decay of amplification efficiency during the reaction can rapidly lead to inaccuracy, even while the slope and linearity of log plots of the competitor input and reaction product ratios are close to ideal. Finally, we show here that competitive RT-PCR reactions do not have to remain in the log-linear phase of PCR in order to accomplish accurate and precise quantification. Using appropriate competitors sharing primer binding sites and high internal sequence similarity, identical amplification efficiencies are preserved throughout the reaction. Reaction products, including heteroduplexes formed between native and competitor templates as reactions progress to plateau, can be identified and quantified accurately using the new technique of denaturing HPLC (dHPLC). This analytical technique allows the accuracy of competitive RT-PCR to be preserved beyond the linear phase. The technique has high sensitivity and precision and target abundances as low as 100 copies could be reliably estimated.

Effects of A-23187 and verapamil on the active transport enzymes in turtle bladder epithelial cells

These experiments were designed to examine the effects of A-23187 (5 x 10(-4) M) and verapamil (100 microM) on membrane transport, 45Ca fluxes, and adenosine-triphosphatase (ATPase) activities in turtle bladder. In the intact membrane, the calcium ionophore decreased proton secretion and sodium transport [short-circuit current (SCC)] to approximately the same degree (by approximately 55% at 30 min). During the same period of time, verapamil decreased SCC (by approximately 58%), but proton secretion was unaffected. The turtle bladder membrane is composed predominantly of two cell types: 1) the mitochondrial-rich cells (MR cells) thought to be involved in proton (and bicarbonate) secretion containing significant H(+)-ATPase and Ca(2+)-ATPase and 2) the granular cells (G cells), postulated important in sodium reabsorption, having abundant Na(+)-K(+)-ATPase. That Na(+)-K(+)-ATPase activity was unchanged by either a calcium ionophore or a calcium channel blocker suggests that the decrease in SCC noted in the intact membrane is not directly mediated by changes in the sodium "pump." The decrease of H(+)-ATPase in MR cells, which resulted after the A-23187, suggests that it probably exerts a direct action on the proton pump, which decreases hydrogen ion secretion. The increase in ATP-dependent 45Ca transport seen after the ionophore (or the decrease in ATP-independent 45Ca transport after verapamil) most likely reflects increased (or decreased) Ca2+ availability within the cytosol, and the high (or low) cell calcium could decrease the SCC. These results thus suggest that cytosolic Ca2+ reciprocally sets, by different mechanisms, the rate of proton secretion in MR cells and the sodium reabsorption in G cells.

A rolB regulatory factor belongs to a new class of single zinc finger plant proteins

A protein which binds to the regulatory domain B necessary for expression of the plant oncogene rolB in (root) meristems contains a single zinc finger of a novel type conserved in dicots and monocots. Band shift analysis revealed the presence in tobacco nuclei of a protein selectively binding to domain B, a tetramer of which was used to isolate a cDNA (NtBBF1, Nicotiana tabacum rolB domain B Factor 1) from a tobacco expression library. The corresponding genomic clone was also isolated. The protein encoded by NtBBF1 contains a single C2C2 zinc finger, and its target sequence in domain B was identified by means of mutagenized oligonucleotides. The DNA-binding capability of the zinc finger was assessed by means of a fusion of this latter with the glutathione-S-transferase protein, that was shown to bind the same target sequence as NtBBF1. A number of other tobacco cDNAs encoding different proteins with a domain (BBF domain) encompassing the zinc finger identical to NtBBF1 were also isolated. Furthermore, a cDNA encoding a protein with an almost identical single zinc finger was isolated from Arabidopsis. A very closely related zinc finger has very recently been identified in maize transcription factors and termed the Dof domain. It is proposed that the tobacco, Arabidopsis and maize BBF/Dof domain proteins are members of a new broad family of plant transcription factors acting through a single zinc finger widely utilized in the plant kingdom.

Pathophysiologic mechanisms in analgesic-induced papillary necrosis

The nonnarcotic analgesics have been implicated as a significant cause of chronic renal failure worldwide. Epidemiologic studies of habitual abuse and necropsy studies show a strong relationship between the two. Animal studies designed to elucidate underlying mechanisms have been hampered because the lesion occurs infrequently and only after very high doses are given for prolonged periods; however, the Fischer 344 and Wistar rats appear to be more sensitive, and substantial new information should be forthcoming. In this review, some of the evidence for the possible mechanisms of papillary necrosis are presented: prostaglandin inhibition, reduction or redistribution of renal blood flow, direct cellular injury, free radical formation, and immunologic injury. At present, most data support prostaglandin inhibition and reduction or redistribution of renal blood flow, but direct cellular injury also appears to be very important.

Studies on the mechanism of trimethoprim-induced hyperkalemia

We examined the effects of trimethoprim (TMP) on metabolic parameters and renal ATPases in rats after a 90 minute infusion (9.6 mg/hr/kg body wt, i.v.) and after 14 days (20 mg/kg body wt/day, i.p.). After one dose of TMP, plasma electrolytes, arterial pH and aldosterone levels were normal, but a natriuresis, bicarbonaturia, and decreased urinary potassium excretion occurred. Na-K-ATPase activity in microdissected segments from these animals was decreased by 36 +/- 0.9% in proximal convoluted tubule (PCT) (P < 0.005); decreases of 50 +/- 2.1% and 40 +/- 1.1% were seen in cortical and medullary collecting tubules (CCT and MCT), respectively (P < 0.005). Na-K-ATPase activity was unaffected in medullary thick ascending limb (MTAL). H-ATPase (in PCT and collecting duct) and H-K-ATPase (in CCT and MCT)-activities were not changed. Following chronic TMP administration, plasma potassium increased as compared to control (5.16 +/- 0.05 mEq/liter vs. 3.97 +/- 0.05 mEq/liter, P < 0.05), however, acid-base status and plasma aldosterone levels were normal. Na-K-ATPase activity was decreased by 45 +/- 2.6% in PCT (P < 0.005), 73 +/- 2.0% in CCT (P < 0.001), and 53 +/- 2.5% in MCT (P < 0.005). Na-K-ATPase, activity in MTAL and H-K-ATPase activity in CCT and MCT were unchanged. H-ATPase activity in PCT and MTAL was normal, but in the collecting tubule (CCT and MCT) it was decreased by approximately 25% (P < 0.05). TMP inhibited Na-K-ATPase activity in a dose-dependent fashion in PCT, CCT, and MCT when tubules from normal animals were incubated in vitro with the drug; TMP in vitro did not affect H-ATPase or H-K-ATPase activity. These results suggest that TMP-induced hyperkalemia may result from decreased urinary potassium excretion caused by inhibition of distal Na-K-ATPase, in the face of intact H-K-ATPase activity.

Accurate and absolute quantitative measurement of gene expression by single-tube RT-PCR and HPLC

We report a method that allows accurate, absolute quantification of gene expression in a single reverse transcriptase (RT)-PCR reaction. This method makes use of novel high-performance liquid chromatography (HPLC) technology to resolve and quantify the products of competitive, mutant RNA PCRs. The HPLC technique allows rapid, high resolution of reaction products. On-line UV detection eliminates the need for radiolabel or other tracers. The HPLC technique also demonstrates that these competition reactions readily generate heteroduplex products. The ability of HPLC to resolve and quantify heteroduplex products is fundamental to the accuracy of the technique. Accurate measurements of gene expression have been obtained over four orders of magnitude and experiments employing predetermined quantities of specific native RNA input have demonstrated the ability of the system to provide absolute estimates of gene expression. Large size differences between native and mutant RNA inputs affected reverse transcriptase (RT) efficiency, but not PCR amplification efficiency. However, the magnitude of the RT efficiency effect can be estimated, is reproducible, and can therefore be adjusted by a calculated correction factor. The RT efficiency difference can been eliminated by reduction in the magnitude of the sequence difference between native and mutant RNA so that no correction factor is required. The application of the technique to quantification of expression of the alpha 1 subunit of sodium, potassium-ATPase in microdissected nephron segments is demonstrated.

Effects of pH on calcium transport in turtle bladder

This study was designed to examine the effect of apical and basolateral (ie, mucosal and serosal) pH on calcium (Ca) transport in turtle bladder, a nonmammalian analog of the distal nephron. Unidirectional Ca45 fluxes were measured when serosal pH was 6.4, 7.4, or 8.4 (mucosal pH, 7.4) in the presence and absence of ouabain. When serosal pH was 8.4, M-->S Ca45 flux increased significantly, and when it was 6.4, M-->S Ca45 flux decreased markedly. Changes in serosal pH did not affect the S-->M Ca45 flux. When 5 x 10(-4) mol/L ouabain was added to inhibit sodium transport, M-->S Ca45 flux, at pH 7.4, was 221.6 +/- 27.4 pmol/mg/h (n = 10), and low pH again inhibited this flux (approximately 50%). Lowering mucosal pH (with serosal pH 7.4) also decreased M-->S Ca45 flux. In stripped bladders, Ca45 uptake increased linearly as medium pH was increased from 4.4 to 8.4. Total tissue Ca concentration did not change when serosal pH was varied, except at the extreme of pH 4.4, where tissue Ca decreased. By contrast, when apical pH was 6.4, tissue Ca rose substantially (approximately 1.5-fold). these results demonstrate that extracellular pH directly affects Ca homeostasis in the turtle bladder. Lowering the pH of either the serosal or mucosal medium directly inhibits apical Ca permeability. This change in Ca permeability is seen in the presence of ouabain. By contrast, alkalization of the serosal medium enhances apical permeability, but this effect is, in some manner, related to sodium transport.(ABSTRACT TRUNCATED AT 250 WORDS)