Carlos Schreck - Academia.edu (original) (raw)

Papers by Carlos Schreck

American Journal of Physiology-renal Physiology, Dec 15, 2015

This study describes a highthroughput fluorescence dilution technique to measure the albumin refl... more This study describes a highthroughput fluorescence dilution technique to measure the albumin reflection coefficient (Alb) of isolated glomeruli. Rats were injected with FITC-dextran 250 (75 mg/kg), and the glomeruli were isolated in a 6% BSA solution. Changes in the fluorescence of the glomerulus due to water influx in response to an imposed oncotic gradient was used to determine Alb. Adjustment of the albumin concentration of the bath from 6 to 5, 4, 3, and 2% produced a 10, 25, 35, and 50% decrease in the fluorescence of the glomeruli. Pretreatment of glomeruli with protamine sulfate (2 mg/ml) or TGF-␤1 (10 ng/ml) decreased Alb from 1 to 0.54 and 0.48, respectively. Water and solute movement were modeled using Kedem-Katchalsky equations, and the measured responses closely fit the predicted behavior, indicating that loss of albumin by solvent drag or diffusion is negligible compared with the movement of water. We also found that Alb was reduced by 17% in fawn hooded hypertensive rats, 33% in hypertensive Dahl salt-sensitive (SS) rats, 26% in streptozotocin-treated diabetic Dahl SS rats, and 21% in 6-mo old type II diabetic nephropathy rats relative to control Sprague-Dawley rats. The changes in glomerular permeability to albumin were correlated with the degree of proteinuria in these strains. These findings indicate that the fluorescence dilution technique can be used to measure Alb in populations of isolated glomeruli and provides a means to assess the development of glomerular injury in hypertensive and diabetic models. kidney; glomerulus; proteinuria; renal hemodynamics; renal disease PROTEINURIA AND MICROALBUMINURIA have long been used as markers for early detection of chronic kidney disease (CKD) (2, 3, 5, 11, 14, 52). Elevated excretion of protein may be a consequence of injury to the glomerular protein permeability barrier, defects in tubular reabsorption of filtered protein, or a combination of both (11, 49, 52). However, the relative contributions of changes in renal hemodynamics vs. alterations in the glomerular permeability barrier to protein in the development of proteinuria are difficult to determine in vivo. Thus it is desirable to develop an in vitro model to study the barrier function of glomerulus in the absence of variation in perfusion pressure.

American Journal of Physiology-renal Physiology, 2012

Epithelial Na ϩ channel (ENaC)-mediated Na ϩ absorption and BK channel-mediated K ϩ secretion in ... more Epithelial Na ϩ channel (ENaC)-mediated Na ϩ absorption and BK channel-mediated K ϩ secretion in the cortical collecting duct (CCD) are modulated by flow, the latter requiring an increase in intracellular Ca 2ϩ concentration ([Ca 2ϩ ]i), microtubule integrity, and exocytic insertion of preformed channels into the apical membrane. As axial flow modulates HCO 3 Ϫ reabsorption in the proximal tubule due to changes in both luminal Na ϩ /H ϩ exchanger 3 and H ϩ-ATPase activity (Du Z, Yan Q, Duan Y, Weinbaum S, Weinstein AM, Wang T. Am J Physiol Renal Physiol 290: F289-F296, 2006), we sought to test the hypothesis that flow also regulates H ϩ-ATPase activity in the CCD. H ϩ-ATPase activity was assayed in individually identified cells in microperfused CCDs isolated from New Zealand White rabbits, loaded with the pHsensitive dye BCECF, and then subjected to an acute intracellular acid load (NH4Cl prepulse technique). H ϩ-ATPase activity was defined as the initial rate of bafilomycin-inhibitable cell pH (pHi) recovery in the absence of luminal K ϩ , bilateral Na ϩ , and CO2/HCO 3 Ϫ , from a nadir pH of ϳ6.2. We found that 1) an increase in luminal flow rate from ϳ1 to 5 nl•min Ϫ1 •mm Ϫ1 stimulated H ϩ-ATPase activity, 2) flowstimulated H ϩ pumping was Ca 2ϩ dependent and required microtubule integrity, and 3) basal and flow-stimulated pHi recovery was detected in cells that labeled with the apical principal cell marker rhodamine Dolichos biflorus agglutinin as well as cells that did not. We conclude that luminal flow modulates H ϩ-ATPase activity in the rabbit CCD and that H ϩ-ATPases therein are present in both principal and intercalated cells.

American Journal of Physiology-renal Physiology, Nov 1, 2011

Apical SK/ROMK and BK channels mediate baseline and flow-induced K secretion (FIKS), respectively... more Apical SK/ROMK and BK channels mediate baseline and flow-induced K secretion (FIKS), respectively, in the cortical collecting duct (CCD). BK channels are detected in acid-base transporting intercalated (IC) and Na-absorbing principal (PC) cells. Although the density of BK channels is greater in IC than PC, Na-K-ATPase activity in IC is considered inadequate to sustain high rates of urinary K secretion. To test the hypothesis that basolateral NKCC in the CCD contributes to BK channel-mediated FIKS, we measured net K secretion (JK) and Na absorption (JNa) at slow (∼1) and fast (∼5 nl·min−1·mm−1) flow rates in rabbit CCDs microperfused in vitro in the absence and presence of bumetanide, an inhibitor of NKCC, added to the bath. Bumetanide inhibited FIKS but not basal JK, JNa, or the flow-induced [Ca2+]i transient necessary for BK channel activation. Addition of luminal iberiotoxin, a BK channel inhibitor, to bumetanide-treated CCDs did not further reduce JK. Basolateral Cl removal reversibly inhibited FIKS but not basal JK or JNa. Quantitative PCR performed on single CCD samples using NKCC1- and 18S-specific primers and probes and the TaqMan assay confirmed the presence of the transcript in this nephron segment. To identify the specific cell type to which basolateral NKCC is localized, we exploited the ability of NKCC to accept NH4+ at its K-binding site to monitor the rate of bumetanide-sensitive cytosolic acidification after NH4+ addition to the bath in CCDs loaded with the pH indicator dye BCECF. Both IC and PC were found to have a basolateral bumetanide-sensitive NH4+ entry step and NKCC1-specific antibodies labeled the basolateral surfaces of both cell types in CCDs. These results suggest that BK channel-mediated FIKS is dependent on a basolateral bumetanide-sensitive, Cl-dependent transport pathway, proposed to be NKCC1, in both IC and PC in the CCD.

Transplantation, Jul 1, 2014

Transplantation Proceedings, Mar 1, 2018

Introduction. Living kidney donor (LKD) transplantation is increasing due to organ shortage. Clin... more Introduction. Living kidney donor (LKD) transplantation is increasing due to organ shortage. Clinical studies have shown that the risk of developing end-stage renal disease (ESRD) in donors is similar to that in the general population. Our goal was to evaluate postdonation renal outcomes assessed by glomerular filtration rate (GFR), proteinuria, and blood pressure. Methods. A total of 210 LKD transplants were performed at Hospital Italiano de Buenos Aires between 2000 and 2014. Postdonation outcomes were analyzed in 109 donors. GFR was assessed by 24-hour creatinine clearance (as 24-hour ClCr) and estimated using the Modification of Diet in Renal Disease (MDRD) and Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations. Additionally, we correlated the predonation renal functional reserve (RFR) with postdonation GFR. Donor results were compared to the expected GFR (adjusted to age and single kidney). Other renal outcome indicators measured were albuminuria and blood pressure, and they were compared (predonation and postdonation) using univariate analysis. Results. A total of 109 patients were followed up for 47 AE 34 months (range, 12e168): 70% were female, age at donation was 48.58 years (range, 25e70), and predonation serum creatinine was 0.85 AE 0.17 mg/dL. Postnephrectomy GFR (24-hour ClCr) was significantly lower compared to predonation GFR (105.38 AE 21.78 mL/min/1.73 m 2 vs 90.14 AE 17.78 mL/min/1.73 m 2). However, postdonation GFR was not significantly different compared to the expected GFR. No differences were found for blood pressure or albuminuria. Age >50 and an RFR (<20%) was associated with a lower GFR. Conclusions. In this population of LKD, renal outcome (24-hour CrCl, albuminuria, and blood pressure) was within the expected outcome for healthy individuals after uninephrectomy.

Transplantation Proceedings, 2020

Background. Pneumonia caused by opportunistic fungi is a serious complication in immunocompromise... more Background. Pneumonia caused by opportunistic fungi is a serious complication in immunocompromised patients. Hypercalcemia has been described in renal transplantation associated with Pneumocystis jirovecii (PJP) or Histoplasma capsulatum (HCP) pneumonia. Methods. We describe 5 patients who underwent kidney transplant between 2014 and 2019 and developed hypercalcemia before the diagnosis of pulmonary fungal infection: 4 patients with PJP and 1 with HCP. We assessed calcium metabolism and kidney function by total and ionized calcium, phosphorus, intact parathormone (iPTH), 25-OH vitamin D, 1,25(OH)2 vitamin D, and serum creatinine levels. Results. Mean albumin-corrected calcium and ionized calcium were 12.56 mg/dL (range, 10.8-13.8 mg/dL) and 1.57 mmol/L (range, 1.43-1.69 mmol/L). Patients were normocalcemic, at 10.12 mg/dL (range, 9.6-10.5 mg/dL), before diagnosis and resolved hypercalcemia after antifungal treatment, at 8.86 mg/dL (range, 8.0-9.5 mg/dL). All patients had low or normal iPTH values, at 29.1 pg/mL (range, <3-44 pg/mL), with higher PTH levels 3 months before diagnosis and after treatment, at 147.3 pg/mL (range, 28.1-479 pg/mL) and 117.5 pg/mL (range, 18.2-245 pg/mL), respectively. The mean value for 25-OH vitamin D was 30.8 ng/mL (range, 14.6-62.8 ng/mL). This supports a PTH-independent mechanism, and we postulated an extrarenal production of 1,25(OH)2 vitamin D. Conclusion. In kidney transplant patients, hypercalcemia independent of PTH and refractory to treatment should alert for the possibility of opportunistic fungal pneumonia.

Transplantation Proceedings, 2016

Background. The Modification of Diet in Renal Disease (MDRD) equation is widely used to estimate ... more Background. The Modification of Diet in Renal Disease (MDRD) equation is widely used to estimate glomerular filtration rate (eGFR) in kidney transplant (KT) patients. The novel Chronic Kidney DiseaseeEpidemiology Collaboration equation (CKD-EPI) could improve accuracy of GFR estimation. Our aim was to compare both equations for staging of CKD in KT patients. Methods. In a cohort of KT patients, correlation of eGFR according to MDRD and CKD-EPI with 24-hour creatinine clearance (24h-CrCl) was evaluated. Concordance between both equations for CKD staging was performed. MDRD was used for initial CKD staging. The mean difference of GFR between 24h-CrCl and each equation was calculated and Bland-Altman analysis applied. Results. A cohort of 463 KT patients were studied: 67% female, overall average age 46 AE 14 years, 41% living donor, mean time of transplantation 71 months (3e95), and mean serum creatinine 1.68 AE 1.03 mg/dL. For the whole cohort (all CKD stages), eGFR by CKD-EPI was 5.33 mL/min/1.73 m 2 higher than by MDRD (P < .01). For CKD stages 1, 2, and 3A, the mean eGFR differences (CKD-EPI À MDRD) were 13.98 AE 3.27, 8.2 AE 1.98, and 5.34 AE 1.32 mL/min/1,73 m 2 , respectively. The percentage of patients with eGFR <60 mL/min/1.73 m 2 decreased from 63.8% according to MDRD to 53.9% with the use of CKD-EPI. In women and patients 65 years old, eGFR by CKD-EPI was 5.98 and 5.81 mL/min/1.73 m 2 higher, respectively, than by MDRD (P < .01). Conclusions. The novel CKD-EPI reduces the number of patients with eGFR <60 mL/ min/1.73 m 2 and consequently assigns lower CKD stages to our KT population.

AJP: Renal Physiology, 2008

The aims of the present study were to determine whether superoxide (O2−) production is enhanced i... more The aims of the present study were to determine whether superoxide (O2−) production is enhanced in medullary thick ascending limb (mTAL) of Dahl salt-sensitive (SS) rats compared with a salt-resistant consomic control strain (SS.13BN) and to elucidate the cellular pathways responsible for augmented O2− production. Studies were carried out in 7- to 10-wk-old male SS and SS.13BN rats fed either a 0.4% NaCl diet or a 4.0% NaCl diet for 3 days before tissue harvest. Tissue strips containing mTAL were isolated from the left kidney, loaded with the O2−-sensitive fluorescent dye dihydroethidium, superfused with modified Hanks’ solution, and imaged at ×60 magnification on a heated microscope stage. O2− production was stimulated in mTAL by incrementing superfusate NaCl concentration from 154 to 254 to 500 mM. O2− production was enhanced in mTAL of SS rats compared with SS.13BN rats in response to incrementing bath NaCl. Addition of N-methyl-amiloride (100 μM) or inhibition of NAD(P)H oxidase...

$Research paper thumbnail of Assessment of fractional excretion of urea for early diagnosis of cardiac surgery associated acute kidney injury$

Renal failure, Jan 23, 2015

Acute kidney injury (AKI) is a common complication after cardiac surgery (CS). Recently, neutroph... more Acute kidney injury (AKI) is a common complication after cardiac surgery (CS). Recently, neutrophil gelatinase-associated lipocalin (NGAL) was shown to predict AKI development earlier than serum creatinine, but it is not widely used in clinical practice. Fractional excretion of urea (FeU) has been referred to as a useful tool to discriminate between prerenal and established AKI. The aim of our study is to evaluate the sensitivity and specificity of FeU, in the early diagnosis of AKI in patients undergoing CS. We performed a prospective study on adults undergoing CS. AKI was defined by AKIN criteria. Individuals suffering from CKD, were excluded. Sensitivity and specificity of FeU, fractional excretion of sodium (FeNa) and urine NGAL, measured at 1, 6 and 24 h following CS, were assessed. We included 66 patients (26% female) aging 68 ± 11 years. AKI prevalence was 24% and mortality was 3.28%. Patients with AKI had a significantly lower FeU compared to those without AKI (23.89 ± 0.67%...

American journal of physiology. Renal physiology, 2017

Within the CCD of the distal nephron of the rabbit, the BK (maxi K) channel mediates Ca2+- and/or... more Within the CCD of the distal nephron of the rabbit, the BK (maxi K) channel mediates Ca2+- and/or stretch-dependent flow-induced K+ secretion (FIKS) and contributes to K+ adaptation in response to dietary K+ loading. An unresolved question is whether BK channels in intercalated cells (ICs) and/or principal cells (PCs) in the CCD mediate these K+ secretory processes. In support of a role for ICs in FIKS is the higher density of immunoreactive apical BKα (pore-forming subunit) and functional BK channel activity than detected in PCs, and an increase in IC BKα expression in response to a high-K+ diet. PCs possess a single apical cilium which has been proposed to serve as a mechanosensor; direct manipulation of cilia leads to increases in cell Ca2+ concentration, albeit of nonciliary origin. Immunoperfusion of isolated and fixed CCDs isolated from control K+-fed rabbits with channel subunit-specific antibodies revealed colocalization of immunodetectable BKα- and β1-subunits in cilia as w...

American Journal of Physiology Regulatory Integrative and Comparative Physiology, Mar 21, 2012

This study examined whether substitution of chromosome 5 containing the CYP4A genes from Brown No... more This study examined whether substitution of chromosome 5 containing the CYP4A genes from Brown Norway rat onto the Dahl S salt-sensitive (SS) genetic background upregulates the renal production of 20-HETE and attenuates the development of hypertension. The expression of CYP4A protein and the production of 20-HETE were significantly higher in the renal cortex and outer medulla of SS.5 BN (chromosome 5-substituted Brown Norway rat) consomic rats fed either a low-salt (LS) or high-salt (HS) diet than that seen in SS rats. The increase in the renal production of 20-HETE in SS.5 BN rats was associated with elevated expression of CYP4A2 mRNA. MAP measured by telemetry rose from 117 Ϯ 1 to 183 Ϯ 5 mmHg in SS rats fed a HS diet for 21 days, but only increased to 151 Ϯ 5 mmHg in SS.5 BN rats. The pressure-natriuretic and diuretic responses were twofold higher in SS.5 BN rats compared with SS rats. Protein excretion rose to 354 Ϯ 17 mg/day in SS rats fed a HS diet for 21 days compared with 205 Ϯ 13 mg/day in the SS.5 BN rats, and the degree of glomerular injury was reduced. Baseline glomerular capillary pressure (Pgc) was similar in SS.5 BN rats (43 Ϯ 1 mmHg) and Dahl S (44 Ϯ 2 mmHg) rats. However, Pgc increased to 59 Ϯ 3 mmHg in SS rats fed a HS diet for 7 days, while it remained unaltered in SS.5 BN rats (43 Ϯ 2 mmHg). Chronic administration of an inhibitor of the synthesis of 20-HETE (HET0016, 10 mg•kg Ϫ1 •day Ϫ1 iv) reversed the antihypertensive phenotype seen in the SS.5 BN rats. These findings indicate that the transfer of chromosome 5 from the BN rat onto the SS genetic background increases the renal expression of CYP4A protein and the production of 20-HETE and that 20-HETE contributes to the antihypertensive and renoprotective effects seen in the SS.5 BN consomic strain. hypertension; glomerulosclerosis; chromosome 5; Dahl S rats; pressure natriuresis; renal hemodynamics; kidney THE DAHL SALT-SENSITIVE (SS) rat is an inbred genetic model that rapidly develops severe hypertension, proteinuria, glomerulosclerosis, and renal interstitial fibrosis when fed a high salt (HS) diet (4, 7-8, 23, 25, 27, 30, 38, 43). However, the genes and pathways that contribute to the development of hypertension and renal disease have yet to be identified. Previous studies from our laboratory have demonstrated that the pressure natriuretic relationship is impaired in SS rats and that this is associated with increased Cl Ϫ transport in the

International Urology and Nephrology, 2007

Hyperkalemia is an unusual complication in peritoneal dialysis patients, having a prevalence of a... more Hyperkalemia is an unusual complication in peritoneal dialysis patients, having a prevalence of around 0.8% among the continuous ambulatory peritoneal dialysis (CAPD) population. The main cause of hyperkalemia in this group is the release of potassium from sources such as gross haematomas and rhabdomyolysis. However, there is no previous report regarding hyperkalemia induced by intracellular potassium shift into the intravascular compartment secondary to druginduced acute hepatitis in peritoneal dialysis. We present the following case report of a peritoneal dialysis patient, well dialyzed and on a lowpotassium diet, who was admitted in our hospital with paralysis secondary to hyperkalemia (serum potassium: 7 mmol/l). Both disorders disappeared using continuous automated peritoneal dialysis (APD) until liver enzymes normalized. We concluded that acute hepatitis can be a cause of hyperkalemia in a properly nourished and welldialyzed peritoneal dialysis patient.

AJP: Regulatory, Integrative and Comparative Physiology, 2011

A fundamental requirement for cellular vitality is the maintenance of plasma ion concentration wi... more A fundamental requirement for cellular vitality is the maintenance of plasma ion concentration within strict ranges. It is the function of the kidney to match urinary excretion of ions with daily ion intake and nonrenal losses to maintain a stable ionic milieu. NADPH oxidase is a source of reactive oxygen species (ROS) within many cell types, including the transporting renal epithelia. The focus of this review is to describe the role of NADPH oxidase-derived ROS toward local renal tubular ion transport in each nephron segment and to discuss how NADPH oxidase-derived ROS signaling within the nephron may mediate ion homeostasis. In each case, we will attempt to identify the various subunits of NADPH oxidase and reactive oxygen species involved and the ion transporters, which these affect. We will first review the role of NADPH oxidase on renal Na+ and K+ transport. Finally, we will review the relationship between tubular H+ efflux and NADPH oxidase activity.

$Research paper thumbnail of Refractory hyperkalemia in peritoneal dialysis$