Biomedical subjects

V L Schuster

Publications and source records attributed to V L Schuster.

50 records · Page 3Linked to original sources

PubMed1987

Coexistent Wegener's granulomatosis and anti-glomerular basement membrane disease.

Wegener's granulomatosis and Goodpasture's syndrome represent two major causes of a pulmonary-renal syndrome. We describe the clinical course and morphologic features of a patient in whom pulmonary manifestations of Wegener's granulomatosis developed and were followed six months later by anti-glomerular basement membrane disease. Although we regard this as a unique and probably fortuitous association, a genetic predisposition or a secondary form of anti-GBM disease cannot be excluded.

Aged↗

PubMed1987

Chloride transport by the cortical and outer medullary collecting duct.

The processes by which chloride is transported by the cortical and outer medullary collecting tubule have been most extensively studied using in vitro microperfusion of rabbit tubules. Chloride appears to be transported by three major mechanisms. First, Cl can be actively reabsorbed by an electroneutral Cl-HCO3 exchanger localized to the apical membrane of the HCO3-secreting (beta-type) intercalated cell. Cl exits this cell via a basolateral Cl channel. This anion exchange process can also operate in a Cl self-exchange mode, is stimulated acutely by beta-adrenergic agonists and cAMP, and is regulated chronically by in vivo acid-base status. Second, Cl can diffuse passively down electrochemical gradients via the paracellular pathway. Although this pathway does not appear to be selectively permeable to Cl, it is large enough to allow for significant passive reabsorption. Third, Cl undergoes recycling across the basolateral membrane of the H+-secreting (alpha-type) intercalated cell. HCO3 exit from this cell brings Cl into the cell via electroneutral Cl-HCO3 exchange; Cl then exits the cell via a Cl channel. Cl transport is thus required for acidification and alkalinization of the urine. Both of these processes exist in the cortical collecting tubule. Their simultaneous operation allows fine tuning of acid-base excretion. In addition, these transport systems, when functioning at equal rates, effect apparent electrogenic net Cl absorption without changing net HCO3 transport. These systems may play an important role in regulating Cl balance.

Animals↗

PubMed1986

Two types of collecting duct mitochondria-rich (intercalated) cells: lectin and band 3 cytochemistry.

Anion exchange plays an important role in renal ion transport and acidification. To further understand the molecular nature of renal epithelial anion exchange, we used a monoclonal antibody to the membrane domain (52 kDa) of human erythrocyte band 3 protein to immunocytochemically search for this polypeptide in the rabbit kidney. In cryostat sections, a subpopulation of cells in the cortical and outer medullary collecting tubules showed immunoreactivity; labeling was restricted to the basolateral membrane. Proximal tubules and thick and thin limbs of Henle showed no immunoreactivity. Approximately 11% of cells in the cortical, but 43% of cells in the medullary, collecting tubule were positive for band 3. To determine the type of cells that were band 3 positive, mitochondria-rich (intercalated) cells were identified by their positive histochemical staining for succinic dehydrogenase activity and by their ability to bind peanut lectin at the apical membrane. In the cortical collecting tubule, the majority of mitochondria-rich cells bound peanut lectin but were band 3 negative; the remainder were band 3 positive but lectin negative. This distribution was reversed in the inner stripe of the outer medulla: all mitochondria-rich cells were band 3 positive and lectin negative. Thus mitochondria-rich cells are of at least two types, each of which has a distinct axial distribution pattern. Given available information about in vitro HCO3 transport properties of rabbit collecting tubules, it is likely that the lectin-positive, band 3-negative mitochondria-rich cells secrete HCO3, whereas the lectin-negative, band 3-positive cells reabsorb HCO3 (secrete H).

Animals↗

PubMed1986

Regulation of chloride self exchange by cAMP in cortical collecting tubule.

The hormonal control of Cl transport was examined in rabbit cortical collecting tubules using the lumen-to-bath 36Cl tracer rate coefficient (KCl, nm/s). Tracer movement via Cl-HCO3 exchange was minimized by using HCO3-CO2-free solutions. The electrical driving force was minimized by treating with amiloride. Under these conditions, net Cl transport was zero, yet there was a large KCl that fell 88% on removing bath (trans) Cl. These results are consistent with the mechanism of tracer flux being predominantly Cl self exchange. KCl fell spontaneously with time in vitro; after this decline KCl could be stimulated with 8-bromo-cAMP. cAMP present from the onset of perfusion prevented the time-dependent fall in KCl. When tracer movement was restricted to diffusion by eliminating Cl self exchange (0 Cl bath), cAMP had no effect on KCl. Although both isoproterenol and vasopressin are known to stimulate adenylate cyclase in this epithelium, only isoproterenol mimicked the cAMP effect on KCl. The isoproterenol effect was blocked by either propranolol or prostaglandin E2. Lumen addition of the disulfonic stilbene DIDS had no effect on KCl. Lumen addition of furosemide or trichloromethiazide had minimal or no effect. Taken together, these results indicate that Cl self exchange is regulated by beta-adrenergic agents acting via cAMP. The lack of an effect of vasopressin suggests cellular heterogeneity in this response to cAMP.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗

PubMed1986

Stimulation of chloride transport by HCO3-CO2 in rabbit cortical collecting tubule.

We examined both the role of HCO3-CO2 in Cl transport as well as the effect of in vivo acid-base status on Cl transport by the rabbit cortical collecting tubule. The lumen-to-bath 36Cl tracer flux, expressed as the rate coefficient KCl, was measured in either HEPES-buffered (CO2-free) or HCO3-CO2-containing solutions. Amiloride was added to the perfusate to minimize the transepithelial voltage and thus the electrical driving force for Cl diffusion. Because KCl fell spontaneously with time in HCO3-CO2 solutions in the absence but not the presence of cAMP, we used cAMP throughout to avoid time-dependent changes. Acute in vitro removal of bath HCO3-CO2 reduced KCl. Acetazolamide addition in HEPES-buffered solutions also lowered KCl; KCl could be restored to control values by adding exogenous HCO3-CO2 in the presence of acetazolamide. In vivo acid-base effects on Cl transport were determined by dissecting tubules from either NaHCO3-loaded or NH4Cl-loaded rabbits. Tubules from HCO3-loaded rabbits had higher rates of Cl self exchange. Acute in vitro addition of bath HCO3-CO2 increased KCl and did so to a greater degree in tubules from HCO3-loaded rabbits. Most of this effect of HCO3-CO2 addition on KCl could not be accounted for by Cl-HCO3 exchange; rather, it appeared due to stimulation of Cl self exchange. The data are consistent with 36Cl transport occurring via Cl-HCO3 exchange as well as Cl self exchange. Both processes are acutely stimulated by HCO3 and/or Co2, and both are chronically regulated by in vivo acid-base status.

8-Bromo Cyclic Adenosine Monophosphate↗

PubMed1986

Effects of inhibitors of Cl conductance on Cl self-exchange in rabbit cortical collecting tubule.

Electroneutral vs. conductive pathways of Cl transport were examined by measuring transepithelial conductance (GT) and the lumen-to-bath 36Cl rate coefficient (KCl). Experimental conditions minimized both Cl-HCO3 exchange [HCO3/CO2-free, N-2-hydroxyethylpiperazine-N'-2-ethane-sulfonic acid (HEPES)-buffered solutions] and the electrical driving force for paracellular Cl diffusion (amiloride in the perfusate, transepithelial voltage near zero). Two agents known to inhibit Cl conductances in other epithelia, anthracene-9-carboxylate (9AC, 1 mM) and diphenylamine carboxylate (DPC, 0.1-0.5 mM) reversibly reduced GT and KCl when added to the bath. Both reduced KCl to values consistent with paracellular diffusion. Bath DPC had no effect on GT in the presence of 4 mM lumen Ba2+, suggesting that the DPC-sensitive conductance is in series with an apical K conductance, i.e., resides on the basolateral membrane. Lumen DPC also reduced GT and KCl, but was less potent than bath DPC. Because the lumen DPC effect on GT was also blocked by lumen Ba2+, lumen DPC probably inhibits a basolateral Cl conductance. K removal and ouabain (0.5 mM) had no effect on KCl, suggesting that Cl tracer movement is not predominantly through the principal cell. We assume that these agents are inhibiting Cl conductive pathways and propose a model in which transcellular Cl movement through the intercalated cell occurs via an apical electroneutral entry step in series with a basolateral conductive pathway.

8-Bromo Cyclic Adenosine Monophosphate↗

PubMed1986

Cyclic adenosine monophosphate-stimulated anion transport in rabbit cortical collecting duct. Kinetics, stoichiometry, and conductive pathways.

Cyclic AMP stimulates HCO3 secretion and Cl self-exchange in rabbit cortical collecting tubule. We found that varying peritubular [Cl] changed the Cl self-exchange rate with saturation kinetics (Km, 3-4 mM). HCO3 secretion also showed saturation kinetics as a function of mean luminal [Cl] (Km, 4-11 mM). Both Cl self-exchange and Cl-HCO3 exchange thus appear to be carrier-mediated. Addition/removal of basolateral HCO3 qualitatively changed Cl and HCO3 transport as expected for Cl-HCO3 exchange, but quantitatively changed Cl absorption more than HCO3 secretion. The diffusive Cl permeability and the transepithelial conductance in the presence of HCO3/CO2 and cAMP were higher than in their absence suggesting that HCO3/CO2 and cAMP together increase a conductive Cl pathway parallel to a 1:1 Cl-HCO3 exchanger. Thus, cAMP not only stimulates the overall process of anion exchange (probably by increasing an electroneutral exchanger and/or a series Cl conductance), but also stimulates a Cl conductance parallel to the exchange process.

Absorption↗

PubMed1986

Effects of angiotensin on proximal tubular reabsorption.

Effects of angiotensin II on rat, rabbit, and bovine proximal tubular reabsorption have been demonstrated with a variety of techniques, including in vivo microperfusion, free-flow micropuncture of surface and juxtamedullary nephrons, perfusion of isolated tubules in vitro, and cell culture. Blockade of endogenous angiotensin production in vivo with converting-enzyme inhibition, or of receptors with saralasin, consistently inhibits proximal reabsorption of fluid in both superficial and juxtamedullary proximal tubules. Angiotensin effects on the proximal tubule are not neurally mediated, for they persist in denervated kidneys and are seen in nerve-free isolated tubules. Physiological concentrations of angiotensin (10(-11)-10(-9) M) stimulate electroneutral sodium transport from the basolateral membrane, whereas pharmacological doses (10(-7) M and above) inhibit reabsorption. The stimulatory effects appear to be receptor mediated. In addition to these direct effects of angiotensin on the proximal tubule epithelium, endogenous angiotensin may also alter peritubular physical forces to further enhance proximal reabsorption. These effects of angiotensin may represent an important homeostatic mechanism during states of extracellular fluid volume depletion.

Angiotensin II↗

PubMed1985

Mechanism of bradykinin, ADH, and cAMP interaction in rabbit cortical collecting duct.

Vasopressin (ADH) and bradykinin (BK) have been shown to stimulate prostaglandin synthesis in rabbit cortical collecting tubules. We studied ADH and BK effects on osmotic water flow (Lp), Na transport (JNa), and transepithelial voltage (VT). Bath BK but not lumen BK blunted subsequent ADH hydroosmotic responses. This BK effect was prevented by ibuprofen or pertussigen pretreatment and was overcome with exogenous cAMP, suggesting that BK, via prostaglandins, interferes with ADH action on Lp at the cAMP generation step. In contrast, bath BK had no effect on bath-to-lumen (Jb-1Na) or lumen-to-bath (Jl-bNa) Na flux or on VT. As reported by others, ADH lowered Jl-bNa and depolarized VT; however, prostaglandin synthesis inhibitors neither prevented nor reversed these ADH effects. Together, these BK and ADH data do not support regulation of JNa by peptide-stimulated prostaglandins. Moreover, cAMP alone depolarized VT but had no effect on Jl-bNa. Therefore, ADH-induced depolarization of VT may at least partly owe to cAMP effects on VT independent of accompanying changes in JNa. As with Lp, bath BK blunted subsequent ADH effects on VT and, to a lesser extent, Jl-bNa; these BK effects on ADH action were also prevented by ibuprofen or pertussigen pretreatment. The data are consistent with the following model: 1) ADH depolarizes VT and increases Lp via cAMP; 2) ADH decreases JNa via neither cAMP nor prostaglandins; and 3) BK, via prostaglandins, inhibits the actions of ADH on Lp and VT at the inhibitory guanyl-nucleotide regulatory subunit of adenylate cyclase.

Adenylate Cyclase Toxin↗

PubMed1985

Calcium balance in uremia: longitudinal study of long-term survivors.

Twelve male patients surviving uremia of 9-15 years duration were studied sequentially over a mean period of 9.2 years. Radiographs, bone biopsies, bone mineral mass (BMM) measured by photon absorptiometry, and total body calcium (TBC) determined by in vivo neutron activation analysis (NAA) were used. Pathologic fractures correlated with TBC corrected for height: 4 of 5 patients without fractures had TBC above 80% predicted, whereas 5 of 7 patients with fractures fell below this value. Unlike previous studies, negative calcium balance was seen in 3 patients with prolonged hyperparathyroidism. Though soft tissue calcification occurred in 6 patients, only 1 with massive shoulder calcification had an increase in TBC; this drawback of NAA has been previously overemphasized. Moreover, radial BMM also increased in 2 patients due to soft tissue calcification. When viewed at a single point in time, nearly all patients fell within the wide normal limits of BMM vs TBC. However, 6 patients with variable bone histology studied sequentially over a mean of 8.5 years showed significant preferential loss of radial bone mass compared to TBC. Aluminium retention did not influence calcium balance in these subjects.

Adult↗

PubMed1985

Cyclic adenosine monophosphate-stimulated bicarbonate secretion in rabbit cortical collecting tubules.

We studied the effects of cyclic AMP (cAMP) on HCO-3 transport by rabbit cortical collecting tubules perfused in vitro. Net HCO-3 secretion was observed in tubules from NaHCO3- loaded rabbits. 8-Bromo-cAMP-stimulated net HCO-3 secretion, whereas secretion fell with time in control tubules. Both isoproterenol and vasopressin (ADH) are known to stimulate adenylate cyclase in this epithelium; however, only isoproterenol stimulated net HCO-3 secretion. The mechanism of cAMP-stimulated HCO-3 secretion was examined. If both HCO-3 and H+ secretion were to occur simultaneously in tubules exhibiting net HCO-3 secretion, cAMP might increase the net HCO-3 secretory rate by inhibiting H+ secretion, by stimulating HCO-3 secretion, or both. These possibilities were examined using basolateral addition of the disulfonic stilbene (4,4'-diisothiocyanostilbene-2,2'-disulfonate (DIDS). In acidifying tubules from NH4Cl-loaded rabbits, DIDS eliminated HCO-3 reabsorption, a result consistent with known effects of DIDS as an inhibitor of H+ secretion. In contrast, cAMP left acidification (H+ secretion) intact. DIDS applied to HCO-3 secretory tubules failed to increase the HCO-3 secretory rate, indicating minimal H+ secretion in HCO-3 secreting tubules. Thus, inhibition of H+ secretion by cAMP could not account for the cAMP-induced stimulation of net HCO-3 secretion. cAMP-stimulated HCO-3 secretion was reversibly eliminated by 0 Cl perfusate, whereas luminal DIDS had no effect. Bath amiloride (1 mM) failed to eliminate cAMP-stimulated HCO-3 secretion when bath [Na+] was 145 mM or 5 mM. cAMP depolarized the transepithelial voltage. The collected fluid [HCO-3] after cAMP could be accounted for by electrical driving forces, suggesting that cAMP stimulates passive HCO-3 secretion. However, cAMP did not alter HCO-3 permeability measured under conditions expected to inhibit transcellular HCO-3 movement (0 Cl- solutions and bath DIDS). This measured HCO-3 permeability was not high enough to account, by passive diffusion, for the HCO-3 fluxes observed in Cl-containing solutions. We conclude the following: cAMP increased net HCO3- secretion by stimulating HCO3- secretion and not by inhibiting H+ secretion; this HCO3- secretion may have occurred by Cl-HCO3- exchange; Na+-H+ exchange appeared not to play a role in basolateral H+ extrusion under these conditions; and the stimulation of HCO3- secretion by isoproterenol, but not ADH, suggests the existence of separate cell cAMP pools or cellular heterogeneity in this cAMP response.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗

PubMed1984

Angiotensin II directly stimulates sodium transport in rabbit proximal convoluted tubules.

Numerous previous studies have proposed a role for angiotensin II (AII) in the renal regulation of salt balance. At least one nephron site, the proximal convoluted segment, has been implicated in this role. We used in vitro microperfusion of rabbit proximal convoluted tubules to further examine this question. To insure use of appropriate in vivo concentrations as well as potency of the hormone in vitro, we measured plasma AII levels by radioimmunoassay in normal, sodium-depleted, and adrenalectomized rabbits, and measured AII activity by bioassay after incubation in various microperfusion baths. Plasma levels ranged from approximately 2 X 10(-11) to 5 X 10(-11) M. AII activity was stable in Ringer's solution plus albumin, but not in rabbit serum or Ringer's solution plus fetal calf serum. In Ringer's solution plus albumin, physiologic concentrations of AII stimulated volume reabsorption (Jv). 10(-11) M AII increased Jv by 16% (P less than 0.01). 10(-10) M AII produced a lesser increase, 7.5% (P less than 0.05). At a frequently studied, but probably pharmacologic dose, 10(-7) M AII inhibited Jv by 24% (P less than 0.001). AII at 10(-11) M did not stimulate Jv in the presence of 10(-7) M saralasin. Though previous studies have suggested agonistic effects of saralasin alone in epithelia, we found no significant effect of 10(-7) M saralasin on Jv. None of the AII doses measurably changed transepithelial voltage. We conclude that AII in physiologic doses directly stimulates Jv in proximal convoluted tubules and this effect is probably receptor mediated and, within the limits of detection, electroneutral.

Absorption↗

PubMed1984

Interactions of lysyl-bradykinin and antidiuretic hormone in the rabbit cortical collecting tubule.

Although intrarenal infusions of kinins produce diuresis, it is not clear to what extent this response is due to hemodynamically mediated medullary washout and/or to direct epithelial effects of kinins. Recent evidence has shown that bradykinin binds to collecting tubules in vitro. We therefore examined the interactions of lysyl-bradykinin and antidiuretic hormone (ADH) with respect to hydraulic conductivity (Lp) in the rabbit cortical collecting tubule perfused in vitro. To ensure adequate substrate for prostaglandin synthesis, the bath contained 2.5 microM arachidonic acid. Arachidonic acid produced no change in base-line Lp and had no effect on the subsequent response to a supramaximal dose of ADH (100 microU/ml). Therefore, all subsequent experiments were done in the presence of arachidonic acid. Lysyl-bradykinin (10(-9)M) added to either the lumen or bath had no effect on base-line Lp. Collecting tubules which were exposed for 1 h to bath lysyl-bradykinin (10(-9)M) had a significantly diminished subsequent Lp in response to ADH (P less than 0.02). In tubules exposed to bath lysyl-bradykinin plus indomethacin (5 microM), the subsequent ADH response was normal. Lysyl-bradykinin (10(-9)M) added to the lumen had no effect on subsequent ADH response. We conclude that lysyl-bradykinin from the basolateral side inhibits the hydroosmotic response of the cortical collecting tubule to ADH, and that this inhibition is probably prostaglandin-mediated. Lysyl-bradykinin does not affect water flow from the luminal surface. These data indicate that the diuresis seen with kinin infusions may result, at least in part, from a direct epithelial effect. They also suggest a role of the renal kallikrein-kinin system in modulating water transport in vivo.

Animals↗

PubMed1976

The effects of temperature and thermal acclimation upon the osmotic properties and nonelectrolyte permeability of liver and gill mitochondria from rainbow trout (Salmo gairdneri).

Thermal acclimation of rainbow trout (Salmo gairdneri) taken from 20 degrees C to 7 degrees C resulted in adaptation of mitochondrial function, as evidenced by increases in the specific activities of NADH- and succinate-cytochrome c reductase of 1.93- and 2.7-fold respectively. Mitochondria from both gill and liver obeyed the Boyle-van't Hoff relationship in the range from 400 to 60 mosM. Thermal acclimation had no effect on the osmotic properties of liver mitochondria, whereas gill mitochondria from cold-acclimated trout were more sensitive to osmotic swelling than mitochondria from warm-acclimated individuals. The non-electrolyte permeability of liver mitochondria was assessed by optically monitoring mitochondrial swelling rates in isosmotic solutions of urea, glycerol, mannitol and glucose. Two parameters of mitochondrial swelling were determined: (a) initial swelling rates, d(1/A)dt, and (b) swelling constants, ks, derived from the time required to swell a fixed volume. Regardless of the assay temperature or the permeant employed, liver mitochondria from cold-acclimated trout exhibited greater initial swelling rates than mitochondria from warm-acclimated trout, indicating properties of temperature-compensated permeability. The apparent ranking of nonelectrolyte permeabilities was urea greater than glycerol greater than mannitol greater than glucose. ks values for urea and glycerol from cold-acclimated trout were greater than values typical of warm-acclimated populations; however ks values for glucose and mannitol were not influenced by thermal acclimation. Regardless of the permeant considered, activation energies for ks values were 3- to 5-fold greater than those for initial swelling rates. The time course of mitochondrial swelling consists of two components, an initial rapid swelling phase characterized by a half-life of 3-12 seconds, and a slower swelling phase characterized by a half life of 1-6 minutes. Initial swelling rates, which approximate the rapid swelling component, are considered to be the least ambiguous index of permeability, whereas ks values are more complex and strongly influenced by the slower swelling component.

Acclimatization↗