Phosphate excess and progressive renal failure: the precipitation-calcification hypothesis.
Explore the source record for details and available documents.
Adult↗
Biomedical subjects
K Lau
Publications and source records attributed to K Lau.
Template supercoiling during ATP-dependent DNA helix tracking: studies with simian virus 40 large tumor antigen.
Incubation of topologically relaxed plasmid DNA with simian virus 40 (SV40) large tumor antigen (T antigen), ATP, and eubacterial DNA topoisomerase I resulted in the formation of highly positively supercoiled DNA. Eukaryotic DNA topoisomerase I could not substitute for eubacterial DNA topoisomerase 1 in this reaction. Furthermore, the addition of eukaryotic topoisomerase I to a preincubated reaction mixture containing both T antigen and eubacterial topoisomerase I caused rapid relaxation of the positively supercoiled DNA. These results suggest that SV40 T antigen can introduce topoisomerase-relaxable supercoils into DNA in a reaction coupled to ATP hydrolysis. We interpret the observed T antigen supercoiling reaction in terms of a recently proposed twin-supercoiled-domain model that describes the mechanics of DNA helix-tracking processes. According to this model positive and negative supercoils are generated ahead of and behind the moving SV40 T antigen, respectively. The preferential relaxation of negative supercoils by eubacterial DNA topoisomerase I explains the accumulation of positive supercoils in the DNA template. The supercoiling assay using DNA conformation-specific eubacterial DNA topoisomerase I may be of general use for the detection of ATP-dependent DNA helix-tracking proteins.
Adenosine Triphosphate↗
Purification and characterization of a central cholinergic enhancing factor from rat brain: its identity as phosphoethanolamine.
A compound that can enhance the apparent synthesis of acetylcholine in cultured explants of the medial septal nucleus has been purified from rat brain and identified as phosphoethanolamine. Acetylcholine synthesis is stimulated two- to threefold in cultures grown for 5 days in the presence of phosphoethanolamine, ethanolamine, or cytidine 5'-diphosphoethanolamine at concentrations above 100 microM. This effect appears to result from an increase in the accumulation of choline via the high-affinity, sodium-dependent uptake mechanism. The development of choline acetyltransferase activity is not affected. Phosphoethanolamine and ethanolamine seem to enhance the ability of developing cholinergic neurons to utilize choline accumulated via the sodium-dependent high-affinity choline uptake mechanism for the preferential production of acetylcholine without increasing the general metabolism of the cultures. Choline itself and its related derivatives are not stimulatory for these effects.
Acetylcholine↗
Studies of the structure of lung surfactant protein SP-A.
SP-A, a glycoprotein of pulmonary surfactant, consists of an NH2-terminal domain containing a collagen-like sequence and a COOH-terminal domain with sequence homology to several Ca2(+)-dependent lectins. We have compared the size, thermal stability, and secondary structure of recombinant SP-A, the product of a fibroblast line transfected with a single human gene encoding SP-A, with natural SP-A isolated from canine and human lungs. Our results suggest both recombinant and natural SP-A are assembled as large oligomers. More variability in the degree of oligomerization was observed with recombinant human SP-A than with natural canine SP-A. As shown by collagenase digestion, the full assembly of protein subunits was dependent on an intact collagen-like domain. The cysteines in the noncollagen domain of SP-A form intrachain bonds between residues 135-226 and 204-218. The circular dichroism spectra of both recombinant and natural SP-A were consistent with the presence of a collagen-like triple helix. As determined by the change in ellipticity at 205 nm, the thermal transition temperatures of canine, natural human, and recombinant SP-A were 51.5, 52.3, and 42.0 degrees C, respectively. These results suggest differences in the assembly and stability of the natural and recombinant proteins.
Amino Acid Sequence↗
Effects of parathyroid hormone on cytosolic free calcium concentration in individual rabbit connecting tubules.
PTH stimulates active Ca reabsorption in isolated perfused rabbit kidney connecting tubules (CNTs). The existence of PTH-sensitive adenylate cyclase and the reproduction of increased epithelial Ca transport by dibutyryl-cAMP suggest that cAMP is the mediator. Accordingly, we studied the effects of PTH and 8-bromoadenosine 3',5'-cAMP (8-Br-cAMP) on cytosolic free calcium concentration [( Ca2+]i) in individual rabbit CNTs. [Ca2+]i was estimated by continuous epifluorescence microscopy of single fura-2-loaded tubules during dual wave-length excitation. In nonperfused controls at 37 degrees C, [Ca2+]i decreased with time. In contrast to vehicle controls, synthetic bovine (1-34) PTH (0.1 nM) increased [Ca2+]i within 4 min, produced a maximal effect in 7.2 min, and sustained its effect for at least 2 min after washout. 8-Br-cAMP (1 mM) mimicked the effect of PTH, but with an earlier onset of action. To test the hypothesis that lumen Ca is the predominant source of the rise in [Ca2+]i, we studied singly perfused CNTs. In the absence of bath and lumen Ca, PTH elicited no rise in [Ca2+]i, implying that intracellular Ca stores are not the major source. In contrast, there was a rise when Ca was replenished in both media. In the continuous presence of bath Ca, lumen Ca was estimated to contribute 65% of the total rise in [Ca2+]i in response to PTH when it was first deleted and then replenished. However, when the sequence of lumen Ca manipulation was reversed, the contributions by lumen and bath Ca were found to be essentially equal. We conclude (a) at a physiologic concentration, PTH increases [Ca2+]i in rabbit CNTs, (b) 8-Br-cAMP mimics this action, implicating cAMP as a second messenger, and (c) the PTH-stimulated rise in [Ca2+]i depends importantly on both bath and tubular luminal fluid Ca.
8-Bromo Cyclic Adenosine Monophosphate↗
Structural comparison of human apolipoproteins B-48 and B-100.
In this study we have investigated the structural relationship between human apolipoproteins B-48 and B-100 by comparing protein structure and by comparing nucleotide sequence from intestinal and hepatic cDNA clones. Sequences from intestinal and hepatic cDNA were identical over the entire distance analyzed (7194 bases), which is more than required to code for B-48. The amino-terminal amino acid sequences from intact B-48 and B-100 proteins were also identical over the entire distance analyzed (16 residues). Additional protein homology was evaluated by the combined techniques of peptide mapping and immunoblotting. Purified B-48 and B-100 were each digested with three different endoproteases, and the resulting peptides were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Peptide bands were then detected by silver stain and by Western blotting with antisera against specific regions of B-48 and B-100. The resulting patterns suggest that B-48 is extensively homologous with the amino-terminal portion of B-100. We have identified only four peptides from B-48 (at least one in each digest) that are absent from the parallel digests of B-100. These peptides appear to arise from the ultimate carboxyl terminus of B-48 and appear to be totally homologous with a region located near the center of B-100. Our observations suggest that mature, circulating B-48 is homologous over its entire length (estimated to be between 2130 and 2144 amino acid residues) with the amino-terminal portion of B-100 and contains no sequence from the carboxyl end of B-100.(ABSTRACT TRUNCATED AT 250 WORDS)
Amino Acid Sequence↗
Expression and characterization of human apolipoprotein A-I in Chinese hamster ovary cells.
We produced human apolipoprotein A-I (apoA-I) in Chinese hamster ovary (CHO) cells. The CHO cells were transfected with an expression plasmid which placed the human apoA-I gene under the direction of the human metallothionein II gene promoter. Isolation of a clonal cell line resulted in high level expression of apoA-I. Greater than 30% of total protein secreted by these CHO cells was apoA-I, which enabled us to purify apoA-I with a single step purification scheme. As a result, large quantities of apoA-I can be produced and isolated without having to rely on plasma sources. Structural characterization of the recombinant apoA-I showed it to be identical to authentic apoA-I from human serum high density lipoprotein. Furthermore, we demonstrated approximately equal to 90% of the apoA-I secreted by CHO cells is processed, mature protein. A portion of the secreted recombinant apoA-I was associated with lipid and floated at a density approximately equal to 1.10 g/ml. Additional analysis identified the presence of five isoforms of apoA-I in the CHO cell conditioned medium. Processing and post-translational modification of the recombinant apoA-I occurred in the CHO cell cultures in the absence of serum components. We conclude that the human apoA-I produced by CHO cells is identical to circulating, mature apoA-I in humans and that recombinant mammalian expression offers an opportunity to investigate apoA-I processing.
Amino Acid Sequence↗
Intraluminal calcium modulates lipid dynamics of rat intestinal brush-border membranes.
The present investigations were performed to evaluate whether calcium modulates the physical state and lipid composition of rat enterocyte plasma membranes in vivo. Ca2+ [CaCl2 (50 mM) in NaCl] or NaCl (vehicle control) was administered to rats by intraluminal (gavage) or intraperitoneal routes. Sixty minutes later, brush-border (BBM) and basolateral membranes (BLM) were prepared from the proximal small intestine. By use of the fluorophores, DL-2-(9-anthroyl)-stearic acid (2-AS), DL-12-(9-anthroyl)-stearic acid (12-AS), and 1,6-diphenyl-1,3,5-hexatriene (DPH), steady-state fluorescence polarization studies demonstrated that intraluminal calcium decreased the fluidity of BBM but not BLM compared with their respective vehicle controls. These alterations in fluidity could, at least in part, be attributed to the concomitant increase in sphingomyelin content and the sphingomyelin/lecithin ratio (mol/mol) observed in the BBM prepared from calcium-gavaged rats. To evaluate the mechanism for these lipid alterations, enzyme activities involved in sphingomyelin synthesis and degradation were measured and revealed an increase in sphingomyelin synthase and a decrease in sphingomyelinase in BBM prepared from calcium-gavaged rats. In contrast, intraperitoneal administration of calcium failed to influence membrane fluidity, lipid composition, or these enzymatic activities in either BBM or BLM.
Animals↗
Surgical thyroparathyroidectomy of the rabbit.
Previous studies in the rabbit suggest resistance to parathyroid hormone (PTH) despite the reported presence of PTH-sensitive adenylate cyclase activity in renal cortical slices and tubules. The lack of response may reflect difficulties with complete parathyroidectomy in this species, which has been reported to possess 32 accessory glands. Aided by systematic histology of tissues extirpated during exploration, we tested the hypothesis that the rabbit possesses only four functional parathyroid glands and that the rabbit kidney is sensitive to the expected physiological actions of endogenous PTH. In all rabbits studied, only four glands could be identified histologically, two within the thyroids and two located in the fascial plane between the sternohyoid and sternothyroid muscles and the carotid artery. Surgical thyroparathyroidectomy markedly reduced serum Ca (6.3 vs. 10.6 mg/dl in sham-operated controls), increased the clearance (C) (3.51 vs. 0.78 ml/min) and fractional excretion (FE) of Ca (44.5 vs. 8.3%) while decreasing CP (1.14 vs. 2.40 ml/min), FEP (14.8 vs. 29.9%) and adenosine 3',5'-cyclic monophosphate (cAMP) excretion (341 vs. 760 pmol/min). These findings demonstrate the feasibility of using the described techniques for complete parathyroidectomy in the rabbit. Furthermore, they document the presence of only four functioning parathyroid glands and the renal sensitivity to endogenous PTH in this species.
Animals↗
Renal excretion of divalent ions in response to chronic acidosis: evidence that systemic pH is not the controlling variable.
Although metabolic acidosis produces calciuric, phosphaturic, and magnesiuric effects, the consequences of chronic respiratory acidosis are unclear. To examine the role of systemic pH on renal divalent metabolism, 4-day balance studies were performed in rats with both metabolic acidosis induced by adding 1.5% NH4Cl to the drinking water, and respiratory acidosis produced by exposure to 10% atmospheric CO2 in an environmental chamber, and in controls pair-fed with each group. By the fourth day, blood pH had decreased to an identical degree with both chronic metabolic and respiratory acidosis and averaged 7.28. As anticipated, chronic metabolic acidosis resulted in significant calciuria, magnesiuria, and phosphaturia. However, despite the similar decrement in blood pH, calcium, phosphorus, and magnesium excretion was similar to that in the pair-fed controls with chronic respiratory acidosis. These findings indicate that a low systemic pH, per se, does not account for the modifications in urinary divalent ion handling that accompany chronic metabolic acidosis. However, additional observations suggest that differences in the intracellular pH of the proximal tubular epithelium may be an important regulatory variable.
Acidosis↗
Correction by 1-25-dihydroxycholecalciferol of the abnormal fluidity and lipid composition of enterocyte brush border membranes in vitamin D-deprived rats.
Weanling male Wistar rats were deprived of dietary and light sources of vitamin D for 11-18 weeks along with age-matched diet vitamin D-repleted controls to evaluate the role of lipid fluidity in the stimulatory effect of calcitriol on Ca transport. The "static" component of fluidity of proximal small intestine brush border membrane, as assessed by steady-state fluorescence techniques using the fluorophore 1,6-diphenyl-1,3,5-hexatriene, was similar between these two groups. In contrast, the "dynamic" component of fluidity, as assessed by DL-2-(9-anthroyl)-stearic acid and DL-12-(9-anthroyl)-stearic acid, was decreased in membranes of D-deprived animals. Lipid composition was analyzed to evaluate the potential mechanism mediating these fluidity changes. In vitamin D-deprived rats, linoleic (18:2) and arachidonic (20:4) acids of the phosphatidylcholine and phosphatidylethanolamine fractions of the membrane were decreased, whereas palmitic (16:0) and stearic (18:0) acids were increased in the phosphatidylethanolamine fraction of the membrane. These associated fatty acyl alterations could explain, at least in part, the differences in membrane fluidity between D-repleted and D-deprived rats. Membrane fluidity, lipid composition, and duodenal Ca transport were also analyzed 1, 2, and 5 h after the acute administration of 1-25-dihydroxycholecalciferol to D-deprived animals. In D-deprived rats, within 1-2 h, this hormone restored to levels of vitamin D-repleted controls the dynamic component of fluidity and concentrations of the same membrane phospholipid fatty acids. Since these changes temporally precede detectable increases in Ca absorption (demonstrable only during the 5th h), these data support the hypothesis that alterations in membrane fluidity and lipid composition may play an important role in the stimulation of intestinal calcium transport by calcitriol.
Animals↗
Acute renal failure and coma secondary to acyclovir therapy.
Explore the source record for details and available documents.
Acute Kidney Injury↗
The significance of white matter lucencies on CT scan in relation to cognitive impairment.
As part of a prospective clinicopathological study a cohort of "normal" elderly volunteers (n = 110) has been investigated with CT scans, psychometric testing (Extended Scale for Dementia) and neurological examination. CT scans were evaluated by a neuroradiologist for the presence or absence of white matter lucencies (WML). WML were defined as patchy or diffuse areas of decreased attenuation involving only white matter and with no change in adjacent ventricles or sulci. The 12 subjects with WML had lower scores on the ESD than the 98 subjects without WML (mean ESD with WML 229.5 +/- 14; without WML 236.7 +/- 8.6, t-test p less than .01) and the difference remains significant even after adjusting for the possible confounding effects of age (ANCOVA, P less than .043).
Aged↗
The EEG in Alzheimer type dementia: lack of progression with sequential studies.
Our findings dispel the commonly held belief that the EEG always worsens progressively in dementia of the Alzheimer's type. In a continuing cohort analytical study of dementia, 139 patients with Alzheimer's disease and 148 controls were studied for EEG abnormalities and progression. EEGs were read without knowledge of the previous EEGs or clinical condition, and classified according to the presence of diffuse delta or theta, bisynchronous spikes, projected activity, and focal activity. EEGs were significantly different in the two groups. EEG scores generally worsened over 1-4 years, but most of the subjects showed no alteration in their EEG scores. A few patients with Alzheimer's disease showed improvement of EEG findings.
Alzheimer Disease↗
Response of spontaneously hypertensive rats to 1,25(OH)2D3 in vivo.
Calcium absorption in spontaneously hypertensive rats (SHR) has been reported to be increased, decreased or not different from their normotensive Wistar Kyoto (WKy) control. One postulated reason for these conflicting results is an abnormal sensitivity to the intestinal effects of 1,25(OH)2D3 (1,25D3). Previous studies in everted duodenal sacs and perfused duodenum examined the acute response to 1,25D3 only in 12-week-old SHR, which however already had higher basal rates of calcium absorption. Inability to stimulate Ca absorption further was an unexcluded possibility. To test this hypothesis more vigorously, balance and in situ duodenal 45Ca uptake studies were performed in SHR and WKy using four separate protocols yielding the following results. First, in response to pharmacological doses of 1,25D3 (25 ng/100 g body wt/day X 3), four-week-old normotensive female SHR had higher net calcium absorption (41.4 vs. 31.1 mg/day; 61.6 vs. 48.1%), similar to the increases seen in the untreated state. These results suggest intrinsic epithelial differences independent of 1,25D3. Ca absorption was similarly higher in 1,25D3 treated male SHR (42.9 vs. 36.7 mg/day; 60.1 vs. 53.7%). Second, at 12 to 14 weeks of age, low doses of 1,25D3 (8 ng/100 g body wt/day X 6) stimulated net Ca absorption in the female SHR (33.0 to 39.1 mg/day), but not in WKy (26.8 to 29.3 mg/day). In the male, positive effects were again seen only in the SHR (25 to 45 mg/day). Third, in response to three weeks of dietary Ca deprivation, in situ duodenal 45Ca uptake, measured in the conscious awake state, was higher in 35-week-old SHR (70.9 vs. 53.0%).(ABSTRACT TRUNCATED AT 250 WORDS)
Aging↗
Chronic DOCA treatment increases Ca absorption: role of hypercalciuria and vitamin D.
To examine the effects of mineralocorticoidism on calcium (Ca) absorption and to define the mechanism, rats received a high-salt diet and injections of vehicle or deoxycorticosterone acetate (DOCA). Net (44.2 vs. 31.4 mg/day) and percent Ca absorption (28.1 vs. 20.1%) was increased after 5 days of DOCA. This was associated with increased duodenal 45Ca uptake. Thus despite the hypercalciuria, Ca balance was similar. Although the hypercalciuria persisted chronically, the gut effects were sustained, which maintained normal ionized Ca, bone Ca, and Ca balance. Urinary cyclic adenosine monophosphate was elevated by DOCA. Compared with appropriate controls, neither DOCA alone nor polydipsia (elicited by dextrose) produced similar magnitudes of hypercalciuria as DOCA plus high-salt diet. These maneuvers also failed to increase Ca absorption. Neutralization of the metabolic alkalosis neither attenuated the DOCA-induced hypercalciuria nor abolished the Ca hyperabsorption. In vitamin D-deprived rats, the hypercalciuria but not the intestinal effects of DOCA were reproduced. Serum 1,25-dihydroxyvitamin D3 levels were increased during chronic DOCA treatment (224 vs. 139 pg/ml). These data best fit the hypothesis that increased Ca absorption is secondary to the calciuric effects of DOCA and high-salt diet and is mediated via the increased parathyroid hormone and 1,25-dihydroxyvitamin D3 activities.
Alkalosis↗
Inhibition of Ca absorptive flux by chlorthalidone in the rat duodenum and colon.
To evaluate the mode and intestinal sites of action of chlorthalidone on Ca transport, balance and flux studies by the Ussing technique were performed in rats fed a low Ca diet throughout the experiment to stimulate Ca absorption. Half of the rats received chlorthalidone (5 mg X kg-1 X day-1) orally for 18 wk, a duration of administration previously shown to yield consistent changes. Net Ca absorption was decreased by chlorthalidone (0.91 +/- 0.07 vs. 1.08 +/- 0.3 mg/day, P less than 0.05), which is similar to prior observations in rats fed a normal Ca diet. Ca balance was unchanged by chlorthalidone (0.34 +/- 0.08 vs. 0.36 +/- 0.05 mg/day) because of concomitant hypocalciuria of similar magnitudes. In the duodenum, chlorthalidone decreased mucosal-to-serosal flux (Jm----s) (96.7 vs. 111.5 nmol X cm-2 X h-1, P less than 0.05). Since serosal-to-mucosal flux (Js----m) was unchanged, net Ca flux (Jnet) was reduced (74.0 vs. 89.6 nmol X cm-2 X h-1, P less than 0.05). Similarly, chlorthalidone selectively inhibited Jm----s in the descending colon (27.0 vs. 36.2 nmol X cm-2 X h-1, P less than 0.01), reducing Jnet (14.3 vs. 23.2 nmol X cm-2 X h-1, P less than 0.005). Short-circuit current and tissue conductance were unaffected. These data suggest that chronic chlorthalidone treatment reduces Ca absorption by inhibiting active calcium transport in the small and large intestine.
Absorption↗
Ca fluxes across duodenum and colon of spontaneously hypertensive rats: effect of 1,25(OH)2D3.
Calcium absorption by spontaneously hypertensive rats (SHR) was variably reported to be different from normotensive Wistar-Kyoto (WKY) controls. Furthermore, blunted responsiveness to the intestinal effects of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] has also been postulated. To evaluate this hypothesis, calcium fluxes were measured by the Ussing technique across duodenum and descending colon with or without prior 1,25(OH)2D3 treatment. Duodenal mucosal-to-serosal calcium flux (Jm----s) (44.9 vs. 52.4 nmol X cm-2 X h-1), serosal-to-mucosal flux (Js----m) (25.6 vs. 28.4 nmol X cm-2 X h-1), and net flux (Jnet) were comparable. 1,25(OH)2D3 increased duodenal Jm----s in both SHR and WKY groups (95.2 and 86.8 nmol X cm-2 X h-1). Js----m was lower in SHR (26.1 vs. 35.6 nmol X cm-2 X h-1, P less than 0.01), although the tendency for a higher Jnet in SHR (68.6 vs. 51.2 nmoles X cm-2 X h-1) was statistically insignificant. Short-circuit current was higher in the colon of SHR, both before and after 1,25(OH)2D3, suggesting increased sodium transport. Basal colonic Jnet was virtually zero in both groups but comparably increased by 1,25(OH)2D3 because of stimulation in only Jm----s. Prevention of hypertension by hydralazine since the 4th wk of age did not alter the findings compared with the hypertensive SHR, suggesting calcium transport rates were unaffected by hypertension. These data indicate that in vitro, duodenal, and colonic active calcium transport by the SHR is similar to WKY. Their normal responses to 1,25(OH)2D3 do not support the hypothesis of intestinal resistance.
Animals↗