Biomedical subjects

C I Whiteside

Publications and source records attributed to C I Whiteside.

30 records · Page 2Linked to original sources

PubMed1993

Isolated rat glomerular cells demonstrate L-type Ca(2+)-channel activity.

The presence of L-type calcium (Ca2+)-channels and the effects of Ca(2+)-channel antagonists on cells of rat glomeruli were investigated. Glomeruli were isolated by graded sieving and after preincubation (10 min) in zero Ca2+, the uptake of 45Ca2+ by glomerular cells was measured. Depolarization with KCl (50 mM) or the dihydropyridine agonist Bay K 8644 (10 microM) stimulated 45Ca2+ uptake by 13% and 24%, respectively, above control (100%), which was inhibited by nifedipine (Nif, 10 microM), P < 0.05, and by both S and R isomers of verapamil (Ver, 10 microM), P < 0.001. In a separate experimental preparation, isolated glomeruli were preloaded (45 min) with 45Ca2+. Following a 45 min perifusion (37 degrees C, CaCl2 1.26 mM, in the absence of 45Ca2+), both KCl (50 mM) and Bay K 8644 (10 microM) induced cellular 45Ca2+ efflux with peak values above control of 11% and 15%, respectively, (P < 0.05). Exposure to Bay K 8644 preceded by depolarization with KCl resulted in enhanced 45Ca2+ efflux identifying the presence of voltage-dependent Ca(2+)-channel activity. Cultured rat mesangial cells grown to confluence on coverslips were preloaded with Fura-2 and cytosolic Ca2+ was measured by microfluorometry. KCl (50 mM), gramicidin (2 microM) and/or Bay K 8644 (6 microM) stimulated Ca2+ influx which was inhibited by Ver (10 microM). Ver did not alter endothelin-stimulated Ca2+ signalling. We conclude that L-type Ca2+ channels are present on both rat glomerular (endothelial and/or mesangial) cells in vivo and on cultured mesangial cells, and their activation may be hormone specific.

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

PubMed1993

Vascular exchange in the kidney. Regional characterization by multiple indicator tomography.

In previous work with the method of multiple indicator dilution (MID), we have established that a spatially distributed model of transcapillary exchange proposed by Goresky, Ziegler, and Bach (GZB) accurately describes, at the in vivo whole-organ level, the handling of extracellular indicators in the canine renal cortex. To date, however, it has not been possible to assess the key hypothesis that GZB corresponds to the actual local mechanism of exchange in vivo and is not just a compact summary of the kidney's average whole-organ behavior. By adapting the MID method to high speed computed tomography (CT), we are now able to report that the GZB mechanism is an accurate description of renal cortical transcapillary exchange down to volumes of cortical tissue comprising no more than a few per cent of the total cortical mass, i.e., containing no more than a few thousand nephrons. A small bolus of iohexol (radiopaque extracellular indicator) or iodipamide ethyl ester microparticles (radiopaque plasma indicator) injected into the renal artery was followed by CT as it passed through the kidney and into the renal vein. Time-attenuation value curves of the two contrast media obtained from the renal vein and from regions of interest in the cortex were then modeled with the GZB mechanism and with a more complex formulation that includes GZB as a limiting case. When applied to the data, the models converged to GZB as the best fit for each region examined. The GZB mechanism is found to provide excellent agreement with the regional data.

Animals↗

PubMed1993

Demonstration of renal tubular flow by selective angiographic computed tomography.

A high-speed computed tomography scanner was used to study the bulk flow of a small bolus of nonionic contrast medium through the renal tubules of five dogs. A 0.5-mL bolus of iohexol 300 (150 mg iodine) was injected rapidly into the renal artery, and transverse images of the kidney were obtained at 15-second intervals over 300 seconds. The mean attenuation values measured in regions of interest in the papilla and the cortex were displayed as a function of time. Curves from the papillary regions of interest showed two peaks, the first corresponding to the passage of the bolus through the loops of Henle that extend into the papilla and the second to the passage of the bolus through the terminal collecting tubules. The cortical regions of interest showed the cortical return peak, which corresponded to the passage of the bolus through the distal convoluted tubules. The peaks generated by this method can be used to measure the transit times of the bolus from the glomeruli to the loops of Henle in the papilla, from the loops of Henle to the distal convoluted tubules, and from the distal convoluted tubules to the distal collecting tubules. The mean total transit time in dehydrated dogs was 169 seconds. The method is compared with contrast-enhanced magnetic resonance imaging (with gadolinium diethylenetriaminepentaacetic acid), which has been used by other researchers for the same purpose.

Animals↗

PubMed1993

Podocytic cytoskeletal disaggregation and basement-membrane detachment in puromycin aminonucleoside nephrosis.

Puromycin aminonucleoside--(PAN) treated rats develop acute nephrotic syndrome, mimicking human minimal lesion disease. In PAN nephrosis, podocyte detachment from the glomerular basement membrane (GBM) is the most likely cause of massive proteinuria in this model. To elucidate further the mechanisms of PAN-induced cellular dysfunction, new methods were employed to visualize podocyte cytoskeletal aggregation and to measure fibrillar attachment to the GBM. Adult Sprague-Dawley rats (n = 4/group) received a single tail-vein injection of PAN (75 mg/kg). On days 1, 2, 3, and 5 following injection, 24-hour urine collections were obtained for creatinine clearance, albuminuria, and total proteinuria. Then kidneys from each group were fixed by perfusion. Podocytic cytoskeleton was visualized by scanning electron microscopy. Subepithelial GBM staining and attachment fiber number, observed on digitized images of transmission electron micrographs, were quantitated with computer-based density analysis. A significant reduction in attachment fiber number in the GBM lamina rara externa occurred by day 5. On scanning electron micrographs, the secondary and tertiary podocytic processes were observed to be formed by highly aggregated cytoskeleton, which became partially disaggregated by day 3, was totally absent by day 5, and normalized by day 20. Immunogold staining revealed that actin and vinculin localized to the tertiary podocytic processes in the normal state were dispersed into the cell body following PAN. Podocyte cytoskeletal disaggregation precedes, and detachment from the GBM occurs simultaneously with, the onset of massive proteinuria in the PAN model.

Actins↗

PubMed1992

Upregulation of D-myo-inositol transport in diabetic rat glomerular cells.

In the streptozotocin (STZ)-treated diabetic rat, reduced glomerular arteriolar resistance leads to raised intraglomerular pressure. Because vasoconstrictor hormones, such as angiotensin II, stimulate arteriolar smooth muscle and mesangial cell contraction via the D-myo-inositol (MI)-dependent transmembrane signaling pathway, in diabetes extracellular D-glucose may inhibit MI transport causing MI depletion, reduced signaling, and hypocontractility. Therefore we studied the regulation of Na-dependent MI transport in the intact cells (mesangial and endothelial) of isolated glomeruli from STZ rats after 2 wk of diabetes, with and without insulin, compared with controls. Specific [3H]MI uptake per milligram glomerular protein (10-150 min, 37 degrees C) was observed in the presence of 0, 5.5, and 30 mM D-glucose using L-[14C]glucose as a marker of nonspecific uptake. D-Glucose competitively inhibited Na-dependent MI transport (maximum velocity) into diabetic and normal glomerular cells. At 5.5 mM D-glucose, MI uptake by diabetic non-insulin-treated glomeruli was increased to 191 +/- 14% (SE) above normal glomeruli. Insulin treatment resulted in less upregulation (116 +/- 11%) of normal MI transport. High glucose concentration did not alter the rate of [3H]MI efflux from preloaded glomerular cells. To determine whether diabetes alters available substrate for transmembrane signaling, after incubation for 120 min, the incorporation of [3H]MI into cellular membrane phosphoinositides and soluble D-myo-inositol phosphates of isolated diabetic and control glomerular cells was compared. Diabetic glomerular cells displayed a significant increase (P less than 0.005) in [3H]MI incorporation into these fractions compared with controls.

Animals↗

PubMed1992

Diabetic rat glomerular mesangial cells display normal inositol trisphosphate and calcium release.

Since diabetes may cause cellular myo-inositol depletion, we investigated whether the observed in vitro hypocontractile response of streptozotocin (STZ)-treated rat glomeruli to angiotensin II (ANG II) is associated with an alteration in inositol trisphosphate (IP3) mobilization of intracellular Ca2+. Contraction of diabetic isolated glomeruli induced by ANG II (5 microM), measured in vitro by changes in the planar area, was reduced by 60%, compared with normal up to 60 min (P < 0.05). In cells of isolated glomeruli, preloaded with myo-[3H]inositol, production of [3H]inositol phosphates ([3H]IPs) and [3H]inositol trisphosphate ([3H]IP3) was analyzed by Dowex chromatography. ANG II (1 microM) evoked an immediate peak (5-10 s) in total [3H]IPs of 60.5 +/- 18.8% (mean +/- SE) above basal (nonstimulated state) in normal glomeruli, and 88.4 +/- 19.4% in diabetic condition [not significant (NS), n = 8]. At 60 s, the normal and diabetic total [3H]IPs responses were not significantly different from each other. The immediate (10 s) [3H]IP3 response from normal glomeruli, 8.1 +/- 7.9% above basal, was not significantly different from that of diabetic glomeruli, 15.7 +/- 7.4%. ANG II receptor-mediated rise in cytosolic Ca2+ in the cells of normal and diabetic isolated glomeruli was compared by measuring the efflux of 45Ca2+. Isolated glomeruli were preloaded with 45Ca2+. Following ANG II stimulation, peak 45Ca2+ efflux values at 1 min were 141.7 +/- 15.9% (normal) vs. 143.7 +/- 7.8% (diabetic) of baseline (100%), respectively (NS, n = 4). Thapsigargin, 2 microM, specifically prevented ANG II-stimulated and IP3-mediated 45Ca2+ efflux (73% inhibition, P < 0.001) from cells of whole glomeruli.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin II↗

PubMed1991

Myo-inositol and D-glucose transport in rat glomerular and cultured mesangial cells.

Myo-inositol (MI) is the precursor of membrane-bound phosphoinositides important for transmembrane signaling. This study examines whether freshly isolated whole glomeruli can be used to characterize intact cell transport kinetics for MI and D-glucose. Transport properties of cultured mesangial cells are compared. Glomeruli greater than 95% tubule free were isolated from Sprague-Dawley rat kidney cortex by means of selective sieving. Scanning electron microscopy revealed substantial damage of glomerular epithelial cells, whereas endothelial and mesangial cells remained intact. Specific [3H]MI uptake (7-180 min, 37 degrees C) was observed in presence of 5.5 mM D-glucose when L-[14C]glucose was used as a marker of nonspecific uptake. With ouabain (3 mM), or when Na was replaced with N-methyl-D-glucamine, choline, or Li, specific MI uptake was reduced by 95%. A single high-affinity, Na-dependent MI transport site on glomerular cells with Km of 16.5 +/- 1.4 (SE) microM and Vmax of 947 +/- 56 (SE) fmol.mg protein-1.min-1 was observed for 0.75-100 microM MI. D-glucose competitively inhibited MI transport. Specific D-[3H]-glucose transport was Na independent. Phlorizin inhibition of D-glucose and MI uptake was in keeping with Na-independent D-glucose transport. Km and Vmax for MI uptake in cultured mesangial cells were 42.7 +/- 7.1 microM and 1,474 +/- 192 fmol.mg protein-1.min-1, respectively. We conclude that freshly isolated glomeruli can be used to study cellular transport function that may be modified in disease states.

Animals↗

PubMed1989

Transglomerular cationic macromolecular flux is mediated by a convection-binding mechanism.

Glomerular polyanion function was explored using charged and neutral [3H]dextrans in the multiple indicator-dilution experiment. Anesthetized dogs received an intrarenal bolus of 125I-labeled albumin (plasma reference), [14C]inulin (glomerular reference) and [3H]dextran (test solute), followed by rapid serial sampling of the renal venous and urine outflows. Reduced urinary recovery of cationic diethylaminoethyl dextrans (DEAE) [3H]dextrans [19.0- to 31.5-A Stokes-Einstein radius (SER)], compared with neutral [3H]dextran indicated intrarenal binding reversed by excess unlabeled cationic dextran. Tubular microperfusion with cationic [3H]dextran confirmed a pretubular binding site (presumed glomerular). The application of a computer-assisted mathematical model of convective flux plus reversible binding revealed that binding affinity increased with molecular size. In vitro high-affinity binding of the same cationic [3H]dextrans to isolated rat glomeruli was also found to increase with molecular size and was inhibited by protamine sulfate. Intrarenal polycation perfusion with protamine sulfate (1.0-3.8 mg/g kidney) or lysozyme (1.1-2.2 mg/g body wt) resulted in intraglomerular binding of anionic [3H]dextran without increased proteinuria or altered glomerular permselectivity to neutral [3H]dextrans less than or equal to 33.0-A SER. Hence, transglomerular cationic solute flux is mediated by a convection-binding mechanism that creates an effective polyvalent barrier.

Animals↗

PubMed1989

The role of angiotensin-II in progressive diabetic glomerulopathy in the rat.

The potential pathogenic role of angiotensin-II (AII) in early progressive diabetic and renal ablation-induced glomerulosclerosis was explored and compared in the Sprague-Dawley (SD) rat and the mongrel dog. Male SD rats were divided into control and streptozotocin-treated (65 mg/kg, iv) groups. Unilateral surgical nephrectomy (Nx) was performed in half of each group. Enalapril (E; 50 mg/liter in the drinking water) was administered to half of each subgroup. Enalapril (high E; 250 mg/liter) was given to another 13 streptozotocin rats. All diabetic rats were treated with sc NPH insulin (4 U/day), and blood glucose was 520 +/- 124 mg/dl (mean +/- SD). Microalbuminuria was measured by RIA in 24-h urine collections; wet kidney weights were compared. [125I]AII binding assays were performed on isolated glomeruli. In control rats the high affinity binding dissociation constant (Kd) was 0.59 +/- 0.15 nM (n = 26; mean +/- SD) and receptor number (Ro) was 732 +/- 195 fmol/mg glomerular protein. At 3 weeks, the diabetic glomerular AII receptor Kd was 0.38 +/- 0.07 nM (n = 6; P less than 0.02 vs. control) and Ro was 784 +/- 97 fmol/mg protein (P = NS vs. control); diabetic high E Kd was 0.39 +/- 0.06 nM (n = 6; P less than 0.02 vs. control), and Ro was 873 +/- 105 fmol/mg protein (P = NS vs. diabetes without E). By 10 weeks, a Kd of 0.49 +/- 0.12 nM (n = 32; P less than 0.01 vs. control) and a Ro of 780 +/- 174 fmol/mg protein (P = NS vs. control) were observed when all of the diabetic group data were pooled. Neither Nx nor low or high dose E altered Ro. This is evidence that intraglomerular AII levels are normal or reduced after diabetes, Nx, or both. In the diabetic group, low dose E partially prevented, and high E abolished, Nx-enhanced microalbuminuria and renal hypertrophy. In nine pancreatectomized insulin-treated mongrel dogs over a 12- to 24-month period, despite moderately poor glucose control (300 +/- 75 mg/dl) and combined unilateral Nx in five dogs (12 months), elevated microalbuminuria was not observed. [125I]AII binding to isolated normal and diabetic dog glomeruli revealed the Kd to be of low affinity (1.86 +/- 0.28 to 13.80 +/- 1.88 nM), identifying the presence of type B receptors. Hence, the SD rat and mongrel dog differ in susceptibility to glomerular AII receptor type and progressive diabetic glomerulopathy.(ABSTRACT TRUNCATED AT 400 WORDS)

Albuminuria↗

PubMed1988

In vivo characterization of insulin uptake by dog renal cortical epithelium.

In vivo 125I-labeled insulin uptake by dog renal tubular epithelium was studied using the single-pass multiple indicator dilution (MID) method and analyzed by a computer-assisted model of transcapillary exchange and substrate-cell interaction. Anesthetized dogs received an intrarenal arterial bolus of multiple tracers: [3H]dextran greater than 70 kDa (plasma reference), [14C]inulin (extracellular reference), and 125I-insulin. Rapid serial sampling of the renal venous and urine outflows was performed. The renal venous outflow curves of 125I-insulin fell below [14C]inulin implying postglomerular extraction and antiluminal membrane (ALM) uptake. The fractional urine recovery of 125I-insulin was less than 0.03, indicating luminal tubular uptake of filtered hormone. After intravenous infusion of unlabeled insulin, repeat MID runs with tracer revealed saturable ALM uptake as evidenced by the 125I-insulin renal venous outflow curves approaching [14C]inulin. Luminal tubular uptake was unchanged and therefore unsaturable. The 125I-insulin renal venous data were studied using three mathematical models, incorporating postglomerular reversible binding, irreversible binding or transport. The best fit was obtained using the transport model. The modeling analysis is consistent with either uptake into a virtual epithelial membrane space (i.e., insulin never enters the cell but binds to or is distributed along the ALM) or insulin actually enters the intracellular compartment. In vivo uptake of 125I-insulin ALM is characterized by a Km of 15.44 nM.

Animals↗

PubMed1982

The role of percutaneous transluminal dilatation in the treatment of transplant renal artery stenosis.

The assessment of percutaneous transluminal dilatation (PTD) as a new therapeutic approach for transplant renal artery stenosis (TRAS) was prompted by allograft loss following surgical treatment. Seventeen (7.0%) of 243 allograft patients had TRAS greater than 80% diagnosed by angiography. The outcome of PTD in 4 TRAS patients was compared to antihypertensive drugs alone in 5 and attempted surgical repair in 8. Patients receiving antihypertensive drugs alone required 3.2 drugs at optimal doses to maintain diastolic BP less than or equal to 90 mm Hg. Malignant hypertension developed in 1 non-compliant patient. Three of the 8 surgical repairs resulted in loss of functioning grafts due to postoperative renal artery thrombosis; the remaining 5 had substantial reduction in diastolic BP (pre 112 +/- 8 mm Hg, post 93 +/- 8 mm Hg, P less than .05). Four patients with main renal artery stenosis had successful, uncomplicated PTD with no graft loss, a significant reduction in diastolic BP (pre 108 +/- 10 mm Hg, post 88 +/- 5 mm Hg, P less than .05) and less antihypertensive drug requirement (pre 3.0 +/- .8 drugs, post 1.0 +/- .8 drugs, P less than .05). Restenosis occurred in 1 patient during the 6 to 10 month follow-up period. PTD compared favourably with conventional management of TRAS as a new therapeutic approach.

Angioplasty, Balloon↗

PubMedDate not supplied

Transmembrane signalling of cholinergic-stimulated contraction in isolated rat glomeruli.

Exposure of isolated rat glomeruli to carbachol (Carb) 1 mM induces glomerular (mesangial cell) contraction which is inhibited by pirenzepine. To identify the cellular signalling mechanism, we analyzed Carb-activated phosphoinositide hydrolysis in myo-[2-3H] inositol preloaded cells of isolated rat glomeruli. Carb evoked a rapid (5 s, 30.4 +/- 8.3% of basal) and sustained (60 s, 157.2 +/- 1.2% of basal) inositol trisphosphate (IP3) response. Acetylcholine 100 microM (Ach) in the presence of eserine also evoked IP3 formation. Mobilization of Ca2+ was monitored by preloading glomerular cells with 45Ca2+ (200 microCi/ml) and analyzing the cellular efflux using a constant perifusion system. Both Carb and Ach induced transient 45Ca2+ efflux, with peak values above baseline of 69.0 +/- 19.9 and 71.5 +/- 7.9%, respectively. Incubation with pirenzepine or prior release of Ca2+ from an IP3-sensitive intracellular pool by Thapsigargin (2 microM) prevented Carb-evoked Ca2+ release (100 and 60%, respectively). Therefore, glomerular cells possess functional cholinergic receptors which stimulate contraction via IP3-mediated intracellular Ca2+ release.

Acetylcholine↗