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D Riccardi

Publications and source records attributed to D Riccardi.

At least 19 recordsLinked to original sources

Altered expression of iron transport proteins in streptozotocin-induced diabetic rat kidney.

Diabetes mellitus is associated with altered iron homeostasis in both human and animal diabetic models. Iron is a metal oxidant capable of generating reactive oxygen species (ROS) and has been postulated to contribute to diabetic nephropathy. Two proteins involved in iron metabolism that are expressed in the kidney are the divalent metal transporter, DMT1 (Slc11a2), and the Transferrin Receptor (TfR). Thus, we investigated whether renal DMT1 or TfR expression is altered in diabetes, as this could potentially affect ROS generation and contribute to diabetic nephropathy. Rats were rendered diabetic with streptozotocin (STZ-diabetes) and renal DMT1 and TfR expression studied using semi-quantitative immunoblotting and immunofluorescence. In STZ-diabetic Sprague-Dawley rats, renal DMT1 expression was significantly reduced and TfR expression increased after 2 weeks. DMT1 downregulation was observed in both proximal tubules and collecting ducts. Renal DMT1 expression was also decreased in Wistar rats following 12 weeks of STZ-diabetes, an effect that was fully corrected by insulin-replacement but not by cotreatment with the aldose reductase inhibitor, sorbinil. Increased renal TfR expression was also observed in STZ-diabetic Wistar rats together with elevated cellular iron accumulation. Together these data demonstrate renal DMT1 downregulation and TfR upregulation in STZ-diabetes. Whilst the consequence of altered DMT1 expression on renal iron handling and oxidant damage remains to be determined, the attenuation of the putative lysosomal iron exit pathway in proximal tubules could potentially explain lysosomal iron accumulation reported in human diabetes and STZ-diabetic animals.

Animals↗

The calcium-sensing receptor as a nutrient sensor.

Critical to cell fate in many cell types is the ability to sense and respond to acute changes in free ionized extracellular calcium concentration ([Ca(2+)](o)). Such tight control is mediated by the activation of a protein known as the extracellular-calcium-sensing receptor (CaR). CaR belongs to the 'family C' of G-protein-coupled receptors and was the first G-protein-coupled receptor to be identified to have an inorganic cation, calcium, as its ligand. While calcium is the physiological agonist of the receptor, several other polyvalent cations and polycations can also modulate CaR function as do certain L-aromatic amino acids, polyamines, salinity and pH. This feature renders the CaR uniquely capable of generating cell- and tissue-specific responses, and of integrating inputs deriving from changes in the Ca(2+)(o) concentration with signals deriving from the local metabolic environment. Here we address the role of the CaR in physiology and disease, the range of CaR modulators and the potential roles of the CaR as a metabolic sensor in a variety of physiological (and pathological) scenarios.

Amino Acids↗

Voltage- and Ca2+-dependent burst generation in neuroendocrine Dahlgren cells in the teleost Platichthys flesus.

The neuroendocrine Type 1 Dahlgren cells of the caudal neurosecretory system of the flounder display characteristic bursting activity, which may increase secretion efficiency. The firing activity pattern in these cells was voltage-dependent; when progressively depolarized, cells moved from silent (approximately -70 mV), through bursting and phasic to tonic firing (< -65 mV). Brief (10 s) evoked bursts of spikes were followed by a slow after-depolarization (ADP; amplitude up to 10 mV, duration 10-200 s), which was also voltage-dependent and could trigger a prolonged burst. The ADP was significantly reduced in the absence of external Ca(2+) ions or the presence of the L-type Ca(2+) channel blocker, nifedipine. BayK 8644 (which increases L-type channel open times) significantly increased ADP duration, whereas the Ca(2+)-activated nonselective cation channel blocker, flufenamic acid, had no effect. Pharmacological blockade of Ca(2+)-activated K(+) channels, using apamin and charybdotoxin, increased the duration of both ADP and evoked bursts. However, action potential waveform was unaffected by either apamin/charybdotoxin, nifedipine, BayK 8644 or removal of external Ca(2+). The short duration (approximately 100 ms), hyperpolarization-activated, postspike depolarizing afterpotentials (DAP), were significantly reduced by nifedipine. We propose that long duration ADPs underlie bursts and that short duration DAPs play a role in modulation of spike frequency.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗

Electrical activity of caudal neurosecretory neurons in seawater- and freshwater-adapted flounder: responses to cholinergic agonists.

The caudal neurosecretory system (CNSS) of the euryhaline flounder is involved in osmoregulatory responses underlying adaptation to seawater and freshwater. This study compared electrophysiological activity and responses to cholinergic agonists in the neuroendocrine Dahlgren cells in an in vitro preparation taken from fully seawater- (SWA) or freshwater-adapted (FWA) fish. Resting membrane and action potential parameters showed few differences between SWA and FWA cells. The hyperpolarisation-activated sag potential and depolarising afterpotential were present under both conditions; however, amplitude of the latter was significantly greater in SWA cells. The proportions of cells within the population exhibiting different firing patterns were similar in both adaptation states. However, bursting parameters were more variable in FWA cells, suggesting that bursting activity was less robust. The muscarinic agonist, oxotremorine, was largely inhibitory in Dahlgren cells, but increased activity in a non-Dahlgren cell population, alpha neurons. Nicotine promoted bursting activity in SWA Dahlgren cells, whereas it inhibited over half of FWA cells.

Acetylcholine↗

Extracellular calcium sensing receptor in human pancreatic cells.

BACKGROUND AND AIMS: The extracellular calcium sensing receptor (CaR) plays a key role in the calcium homeostatic system and is therefore widely expressed in tissues involved in calcium metabolism. However, the CaR has also been identified in other tissues where its role is less clear. We have investigated the presence of the CaR in the human pancreas. METHODS: Messenger RNA for the CaR was detected by reverse transcription-polymerase chain reaction and the protein was localised by immunostaining. CaR function was assayed in Capan-1 cells by measuring intracellular calcium and [(3)H] thymidine incorporation. RESULTS: The receptor was highly expressed in human pancreatic ducts. It was also expressed in exocrine acinar cells, in islets of Langerhans, and in intrapancreatic nerves and blood vessels. The CaR was expressed in both normal and neoplastic human tissue samples but was detected in only one of five ductal adenocarcinoma cells lines examined. Experiments on the CaR expressing adenocarcinoma cell line Capan-1 showed that the CaR was functional and was linked to mobilisation of intracellular calcium. Stimulation of the CaR reduced Capan-1 cell proliferation. CONCLUSIONS: We propose that the CaR may play multiple functional roles in the human pancreas. In particular, the CaR on the duct luminal membrane may monitor and regulate the Ca(2+) concentration in pancreatic juice by triggering ductal electrolyte and fluid secretion. This could help to prevent precipitation of calcium salts in the duct lumen. The CaR may also help to regulate the proliferation of pancreatic ductal cells.

Adenocarcinoma↗

Cellular localization of divalent metal transporter DMT-1 in rat kidney.

We have demonstrated that the kidney plays an important role in iron balance and that metabolically significant reabsorption of this ion occurs in the loop of Henle and the collecting ducts [Wareing M, Ferguson CJ, Green R, Riccardi D, and Smith CP. J Physiol (Lond) 524: 581-586, 2000]. To test the possibility that the divalent metal transporter DMT1 (Gunshin H, Mackenzie B, Berger UV, Gunshin Y, Romero MF, Boron WF, Nussberger S, Gollan JL, and Hediger MA. Nature 388: 482-488, 1997) could represent the apical route for iron entry in the kidney, we raised and affinity-purified an anti-DMT-1 polyclonal antibody and determined DMT-1 distribution in rat kidney by Western analysis, immunofluorescence, and confocal microscopy. The strongest DMT1-specific (i.e., peptide-protectable) immunoreactivity was found in the collecting ducts, in both principal and intercalated cells. Thick ascending limbs of Henle's loop and, more intensely, distal convoluted tubules exhibited apical immunostaining. Considerable intracellular DMT-1 immunoreactivity was seen throughout the nephron, particularly in S3 segments. The described distribution of DMT-1 protein is in agreement with our previous identification of nephron sites of iron reabsorption, suggesting that DMT-1 provides the molecular mechanism for apical iron entry in the distal nephron but not in the proximal tubule. Basolateral iron exit may be facilitated by a different system.

Animals↗

In vivo characterization of renal iron transport in the anaesthetized rat.

1. In vivo microinjections of 55FeCl3 were made to assess renal iron (Fe2+/3+) transport in the anaesthetized rat. 2. Following microinjection into proximal convoluted tubules (PCTs), 18.5 +/- 2.9 % (mean +/- s.e.m., n = 11) of the 55Fe was recovered in the urine. This recovery was not dependent on the injection site indicating that iron is not reabsorbed across the surface convolutions of the proximal tubule. 3. Following microinjection into distal convoluted tubules (DCTs) 46.1 +/- 6.1 % (n = 8) of the injected 55Fe was recovered. Taken together the recovery data from the PCT and DCT microinjection studies indicate that the transport of iron occurs in the loop of Henle (LH) and collecting duct system. 4. In vivo luminal microperfusion was used to examine iron transport by the LH in more detail. In tubules perfused with 7 micromol l-1 55FeCl3, 52.7 +/- 8. 3 % (n = 8) of the perfused 55Fe was recovered in the collected fluid, indicating significant iron reabsorption in the LH. Addition of copper (Cu2+ as 7 micromol l-1 CuSO4), manganese (Mn2+ as 7 micromol l-1 MnSO4) or zinc (Zn2+ as 7 micromol l-1 ZnSO4) to the perfusate did not affect reabsorption of water, Na+ or K+, but increased recovery of 55Fe to 83.5 +/- 6.8 % (n = 8, P < 0.04), 75.8 +/- 5.9 (n = 6, not significant, n.s.) and 67.9 +/- 3.8; (n = 9, n.s. ), respectively. 5. Thus, iron transport in the LH can be reduced by the addition of copper or manganese to the luminal perfusate suggesting that these ions may compete with iron for a common transport pathway. However, this pathway may not be shared by zinc.

Anesthesia↗

Calcium ions as extracellular, first messengers.

Ca2+ concentration in the extracellular fluids ([Ca2+]o) is essential for a number of vital processes from bone formation to blood clotting. For this reason, it is necessary that [Ca2+]o must be strictly controlled. Mammalian species have developed a complex homeostatic system that includes parathyroid glands, kidney and bone. The extracellular Ca(2+)-sensing receptor (CaR) is an essential component of this system, regulating parathyroid hormone secretion, calcium excretion by the kidney and bone remodeling. Initially identified from bovine parathyroid glands (1), within the five years following its identification CaR presence has rapidly been extended to organs where the link with mineral ion metabolism has not been elucidated (i.e., brain, stomach, eye, skin, and many other epithelial cells) (see 2 for review). This review will address the discovery of a novel class of ionsensing receptors, receptor-effector coupling, and the roles of the CaR inside and outside the Ca2+o homeostatic system.

Animals↗

Dietary phosphate and parathyroid hormone alter the expression of the calcium-sensing receptor (CaR) and the Na+-dependent Pi transporter (NaPi-2) in the rat proximal tubule.

Dietary phosphate (Pi) intake and parathyroid hormone (PTH) are essential regulators of proximal tubular (PT) Pi reabsorption; both factors are associated with adaptive changes in PT apical brush border membrane (BBM) Na/Pi-cotransport activity and specific transporter protein (NaPi-2) content. Urinary Pi excretion is also inversely correlated with luminal Ca2+ concentration ([Ca2+]) both in a PTH-dependent and -independent fashion. A cell-surface, Ca2+(/polyvalent cation)-sensing receptor (CaR) has been localized to the PT BBM with unknown function. To investigate whether PTH and/or dietary Pi intake could affect the distribution or the expression of the CaR, we evaluated their effects on rat kidney CaR and the NaPi-2 expression by Western blot analysis and immunofluorescence microscopy. A chronic high-Pi (1.2%) versus low-Pi (0.1%) diet and acute PTH (1-34) infusion significantly reduced the PT BBM expression of both NaPi-2 and CaR proteins. CaR-specific immunoreactivity in nephron segments other than the PT was not affected by PTH or Pi intake. These results suggest that reduced renal PT CaR expression by a high-Pi diet and by increased circulating PTH levels could contribute to the local control of PT handling of Ca2+ and Pi.

Animals↗

Molecular and functional identification of a Ca2+ (polyvalent cation)-sensing receptor in rat pancreas.

The balance between the concentrations of free ionized Ca2+ and bicarbonate in pancreatic juice is of critical importance in preventing the formation of calcium carbonate stones. How the pancreas regulates the ionic composition and the level of Ca2+ saturation in an alkaline environment such as the pancreatic juice is not known. Because of the tight cause-effect relationship between Ca2+ concentration and lithogenicity, and because hypercalcemia is proposed as an etiologic factor for several pancreatic diseases, we have investigated whether pancreatic tissues express a Ca2+-sensing receptor (CaR) similar to that recently identified in parathyroid tissue. Using reverse transcriptase-polymerase chain reaction and immunofluorescence microscopy, we demonstrate the presence of a CaR-like molecule in rat pancreatic acinar cells, pancreatic ducts, and islets of Langerhans. Functional studies, in which intracellular free Ca2+ concentration was measured in isolated acinar cells and interlobular ducts, show that both cell types are responsive to the CaR agonist gadolinium (Gd3+) and to changes in extracellular Ca2+ concentration. We also assessed the effects of CaR stimulation on physiological HCO3- secretion from ducts by making measurements of intracellular pH. Luminal Gd3+ is a potent stimulus for HCO3- secretion, being equally as effective as raising intracellular cAMP with forskolin. These results suggest that the CaR in the exocrine pancreas monitors the Ca2+ concentration in the pancreatic juice, and might therefore be involved in regulating the level of Ca2+ in the lumen, both under basal conditions and during hormonal stimulation. The failure of this mechanism might lead to pancreatic stone formation and even to pancreatitis.

Animals↗

Expression of cartilage-derived retinoic acid-sensitive protein during healing of the rat tooth-extraction socket.

Cartilage-derived retinoic acid sensitive protein (CD-RAP) is a recently described, cartilage-specific protein. During early healing of the tooth-extraction socket, cells express both chondrogenic and osteogenic cell markers, but no cartilage is formed. Cartilaginous collagen type II protein, a major constituent of hyaline cartilage, has not been detected in the healing socket, although type IX collagen, which coats these fibres, has been detected transiently in early socket healing. This study investigated the spatial and temporal expression of CD-RAP and various osteoblast cell markers, i.e., alkaline phosphatase, osteopontin, osteonectin and osteocalcin, during healing. Immunolocalization of these proteins was determined in the rat tooth socket at 3, 4, 5, 6, 7, 8, 10 and 14 days after extraction. CD-RAP was expressed by preosteoblast cells maximally at 6, 7, and 8 days after extraction. Fully differentiated osteoblasts expressed osteocalcin, a specific osteoblast marker. Preosteoblasts and fibroblasts did not express osteocalcin. On double immunofluorescent staining, some preosteoblasts coexpressed CD-RAP (indicative of chondrogenic differentiation), and either alkaline phosphatase or osteopontin (markers of osteogenic stem-cell maturation). There was no colocalization between osteopontin and osteonectin. CD-RAP was unique amongst the cell markers used in that it was expressed by preosteoblasts, but not by osteoblasts lining the newly formed trabeculae. CD-RAP may have an important role in osteoblast cell differentiation during bone healing.

Alkaline Phosphatase↗

Nutritional Management of Patients With Esophageal and Esophagogastric Junction Cancer.

BACKGROUND: Malnutrition is common in patients with esophageal and esophagogastric cancer. Compared to patients with other digestive and extradigestive neoplasia, the highest incidence (78.9%) was found in those with esophageal cancer. Malnutrition is associated with postoperative complications, increased morbidity, and prolonged hospital stays. METHODS: The authors review the impact and causes of malnutrition in esophageal cancer patients and present strategies that can be used to preserve or restore the nutritional status in this patient population throughout treatment. RESULTS: Patients usually are unable to sustain weight on oral intake alone and require additional means of nutritional support. Several methods can be used to provide nutritional care to the esophageal cancer patient, such as diet modification, oral supplementation, and enteral or parenteral nutrition. The enteral route is preferred due to preservation of gut integrity, reduced risk of complications, and less expense. In terminally ill patients, minimal nutritional intervention may be all that is needed to achieve patient comfort. CONCLUSIONS: In order to improve clinical outcomes and the quality of life for patients with esophageal and esophagogastric cancers, the extent of malnutrition must be identified and treated.

Journal Article↗

Effects of supplementation with unsaturated fatty acids on plasma and membrane lipid composition and platelet function in patients with cirrhosis and defective aggregation.

BACKGROUND/AIMS: Defective platelet aggregation and reduced platelet production of thromboxane A2, a metabolite of arachidonic acid, are common findings in patients with cirrhosis. We evaluated the effects of dietary supplementation with two combinations of unsaturated fatty acids on platelet function and plasma and membrane fatty acids in patients with liver cirrhosis. METHODS: In a double-blind study, 15 patients with cirrhosis and defective aggregation were randomized to receive a 6-week supplementation with gamma-linolenic and linoleic acid (1 g/day of each fatty acid) or with oleic acid and linoleic acid (groups GLA and OA, respectively). RESULTS: Under baseline conditions, patients showed elevated concentrations of monounsaturated fatty acids and a reduction in polyunsaturated fatty acids. The product/precursor ratios for delta6 and delta5 desaturases, two key enzymes in the pathway leading to arachidonic acid, were significantly reduced in the group of patients. In the GLA group, a significant increase in the levels of dihomo-gamma-linolenic acid (20:3omega6) was observed in plasma and membranes, together with a parallel decrease in the 20:4/20:3omega6 ratio after supplementation. No significant changes were observed in the OA group. The levels of arachidonic acid did not change significantly in either group of patients. Platelet aggregation to collagen was unchanged in the GLA group, but significantly improved in the OA group. CONCLUSIONS: These results show that supplementation with precursors of arachidonic acid is ineffective in elevating plasma or membrane arachidonate levels and does not improve platelet aggregation, suggesting that synthesis of arachidonic acid through the delta5 desaturase cannot be correspondingly activated or that incorporation/retention of the produced fatty acid into lipids is impaired. The increased platelet aggregation in the OA group is likely to be explained by the effect of oleic acid contained in the diet, the effects of which may have been counteracted by the elevation in 20:3omega6, a source of anti-aggregatory prostanoids, in the GLA group.

Aged↗

Identification and localization of extracellular Ca(2+)-sensing receptor in rat intestine.

The extracellular calcium (Ca2+o)-sensing receptor (CaR) plays vital roles in Ca2+o homeostasis, but no data are available on its expression in small and large intestine. Polymerase chain reaction products amplified from reverse-transcribed duodenal RNA using CaR-specific primers showed > 99% homology with the rat kidney CaR. Northern analysis with a CaR-specific cRNA probe demonstrated 4.1- and 7.5-kb transcripts in all intestinal segments. Immunohistochemistry with CaR-specific antisera showed clear basal staining of epithelial cells of small intestinal villi and crypts and modest apical staining of the former, whereas there was both basal and apical staining of colonic crypt epithelial cells. In situ hybridization and immunohistochemistry also demonstrated CaR expression in Auerbach's myenteric plexus of small and large intestines and in the submucosa in the region of Meissner's plexus. Our results reveal CaR expression in several cell types of small and large intestine, in which it may modulate absorptive and/or secretomotor functions.

Animals↗

Localization of the extracellular Ca2+/polyvalent cation-sensing protein in rat kidney.

We previously identified transcripts encoding a G protein-coupled, extracellular calcium/polyvalent cation-sensing receptor, RaKCaR, in rat kidney (D. Riccardi, J. Park, W.-S. Lee, G. Gamba, E. M. Brown, and S. C. Hebert. Proc. Natl. Acad. Sci. USA 92:131-135, 1994), which was proposed to provide the mechanism for modulating a variety of renal functions in response to changes in extracellular Ca2+ (E. M. Brown. In: Handbook of Physiology. Bethesda, MD: Am. Physiol. Soc., 1992, sect. 8, vol. 2, chapt. 39, p. 1841-1916; and S. C. Hebert. Kidney Int. 50: 2129-2139, 1996). Here, we examine the cellular and regional distribution of receptor protein by immunofluorescence microscopy using a polyclonal antibody raised against a 22 amino acid region of the NH2 terminus of the receptor. The most intense fluorescence was seen at the basolateral border of cortical thick ascending limb cells. Basolateral staining for the receptor was also detected in medullary thick ascending limbs, in macula densa cells identified by costaining with antibody to brain nitric oxide synthase, NOS-B1, and in distal convoluted tubule cells distinguished by costaining for the apical thiazide-sensitive Na(+)-Cl- cotransporter. Apical anti-RaKCaR staining was detected at the base of the brush border of proximal tubules with decreasing intensity from S1 to S3 segments. In cortical collecting ducts, anti-RaKCaR staining was detected in some, but not all, type A intercalated cells identified by costaining with anti-H(+)-ATPase and anti-AE1 Cl-/HCO3- exchanger antibodies. The present study demonstrates that RaKCaR protein is expressed in many different nephron segments and that the polarity of receptor expression varies with cell type along the nephron. These results suggest potential roles for the extracellular Ca2+/ polyvalent cation-sensing receptor in responding to both circulating and urinary concentrations of divalent minerals and potentially other polyvalent cations (e.g., aminoglycoside antibiotics) to modulate nephron function.

Animals↗

Altered cardiovascular responsiveness to active tilting in nonalcoholic cirrhosis.

BACKGROUND & AIMS: The hyperdynamic circulation of cirrhosis has been related either to plasma volume expansion (increased preload) or peripheral arterial vasodilation (reduced afterload). The aim of this study was to evaluate cardiovascular function in patients with nonalcoholic cirrhosis by echocardiography. METHODS: Nineteen patients with abnormal sodium handling (11 sodium excretors and 8 sodium retainers) and 15 healthy volunteers underwent echocardiographic evaluation of left ventricular end-diastolic volume index (LVEDVI) and left ventricular end-systolic volume index (LVESVI), left ventricular ejection fraction (LVEF), cardiac index (CI), mean arterial pressure, and systemic vascular resistance (SVR) during supine resting and after 5 minutes of standing. RESULTS: Supine patients had increased LVEF and CI and reduced LVESVI and SVR. LVEDVI was increased only in sodium excretors. Standing induced a decrease in LVEDVI in all subjects. Healthy volunteers maintained cardiovascular homeostasis by increasing LVEF and heart rate, whereas cirrhotic patients experienced a decrease in SVI and CI despite marked increments in heart rate, plasma renin activity, and plasma norepinephrine level. CONCLUSIONS: In patients with cirrhosis, the increased LVEF and reduced LVESVI while in a supine position point at reduced afterload as an important determinant of the hyperdynamic circulation. Evidence of an increased preload secondary to increased blood volume, indicated by a high LVEDVI and increased plasma atrial natriuretic peptide levels, was found only in sodium excretors. The altered response to active tilt in cirrhotic patients suggests an impaired myocardial contractility.

Adult↗

Use of SERVQUAL to assess clinicians' satisfaction with the blood transfusion service.

BACKGROUND AND OBJECTIVES: Limited information is available on the level of satisfaction of clinicians with services delivered by blood banks. The purpose of this study was to evaluate the satisfaction of clinicians with our blood transfusion service. MATERIALS AND METHODS: We prepared a questionnaire based on SERVQUAL, a method used to measure customers' appreciation of quality of service, by assessing the gap between perceived and expected quality. The questionnaire consisted of 14 items grouped according to five dimensions of quality of service: assurance, empathy, responsiveness, reliability, tangibles. Clinicians were asked to give two scores on a scale from 1 to 7 for each item, score (e) representing what they expected from an 'excellent' service, score (r) how they graded the service received. We considered wide differences in scores of service expectation and receipt for a question to be indicative of either service above expected levels (r > e) or service below expectation (r < e); similar scores for both expected and received service (within 1 point on the grading scale) were taken to indicate that the service received was that which was expected. RESULTS: A total of 184 questionnaires (49%) were returned. For the 14 items considered, the proportion of clinicians expressing levels of satisfaction similar to or above expectation ranged from 67 to 96%. Three critical areas, which clinicians considered important (expectation scores 6-7) were associated with satisfaction below expectation in more than 20% of responders. They were: clarity of procedures, clarity of blood request forms, and convenience of blood request and issuing times, which were rated as important by 77, 80 and 72% of clinicians, respectively. CONCLUSION: SERVQUAL was useful to gather information on the level of clinicians' satisfaction with our transfusion service.

Ancillary Services, Hospital↗