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Biomedical subjects

S Sabatini

Publications and source records attributed to S Sabatini.

At least 19 recordsLinked to original sources
PubMed1995

Effects of pH on calcium transport in turtle bladder.

This study was designed to examine the effect of apical and basolateral (ie, mucosal and serosal) pH on calcium (Ca) transport in turtle bladder, a nonmammalian analog of the distal nephron. Unidirectional Ca45 fluxes were measured when serosal pH was 6.4, 7.4, or 8.4 (mucosal pH, 7.4) in the presence and absence of ouabain. When serosal pH was 8.4, M-->S Ca45 flux increased significantly, and when it was 6.4, M-->S Ca45 flux decreased markedly. Changes in serosal pH did not affect the S-->M Ca45 flux. When 5 x 10(-4) mol/L ouabain was added to inhibit sodium transport, M-->S Ca45 flux, at pH 7.4, was 221.6 +/- 27.4 pmol/mg/h (n = 10), and low pH again inhibited this flux (approximately 50%). Lowering mucosal pH (with serosal pH 7.4) also decreased M-->S Ca45 flux. In stripped bladders, Ca45 uptake increased linearly as medium pH was increased from 4.4 to 8.4. Total tissue Ca concentration did not change when serosal pH was varied, except at the extreme of pH 4.4, where tissue Ca decreased. By contrast, when apical pH was 6.4, tissue Ca rose substantially (approximately 1.5-fold). these results demonstrate that extracellular pH directly affects Ca homeostasis in the turtle bladder. Lowering the pH of either the serosal or mucosal medium directly inhibits apical Ca permeability. This change in Ca permeability is seen in the presence of ouabain. By contrast, alkalization of the serosal medium enhances apical permeability, but this effect is, in some manner, related to sodium transport.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

The effect of pregnancy on renal function: physiology and pathophysiology.

Marked changes in renal function occur with pregnancy. We present a summary of these changes in this review and give insight into possible mechanisms if they are known. Controversies exist regarding the therapy of pregnancy-induced hypertension and asymptomatic and recurrent bacteriuria. The current views on these topics are given. Specific renal diseases are summarized, including transplantation, and optimum management strategies and maternal and fetal prognosis during pregnancy are given.

Antihypertensive Agents↗
PubMed1992

Vanadate causes hypokalemic distal renal tubular acidosis.

Considerable evidence supports the presence of an H(+)-K(+)-ATPase along the mammalian nephron. Inhibition of this enzyme might be expected to reduce acid excretion while increasing potassium excretion, thus causing hypokalemic distal renal tubular acidosis (RTA). In this study we administered vanadate at a dose of 5 mg/kg ip for 10 days to rats. These animals developed hypokalemic distal RTA with a blood pH of 7.22 +/- 0.01, a plasma bicarbonate of 15.2 +/- 0.6 meq/l, and a plasma potassium of 3.28 +/- 0.06 meq/l. The vanadate-treated animals had a urine pH of 6.70 +/- 0.09, a value significantly higher than NH4Cl-treated animals with the same degree of acidemia (urine pH = 5.25 +/- 0.04). When cortical collecting tubules (CCT) from these animals were microdissected and H(+)-K(+)-ATPase was measured, it was decreased by approximately 75% (P less than 0.001); but H(+)-ATPase was no different from control. In medullary collecting tubule, H(+)-K(+)-ATPase was also decreased but less than in CCT. Muscle potassium concentration in the vanadate-treated animals was significantly lower than in controls. These results demonstrate that vanadate causes hypokalemic distal RTA in association with inhibition of collecting tubule H(+)-K(+)-ATPase activity.

Acidosis↗
PubMed1992

Effect of lithium and amiloride on collecting tubule transport enzymes.

In humans and animals, the administration of Li or amiloride results in a defect in urinary acidification. Both agents are thought to cause this by a voltage-dependent mechanism in the distal nephron. This study was designed to determine the effects of chronic Li and amiloride administration on the two main transport enzymes in rat nephron collecting tubule, the Na-K-adenosine triphosphatase (ATPase) and the H(+)-ATPase. We also examined the effects of both agents on these enzymes in vitro. Amiloride administration resulted in a decrease in Na-K-ATPase and H(+)-ATPase activities in cortical collecting tubule and medullary collecting tubule. Therapeutic concentrations of amiloride in vitro inhibited Na-K-ATPase activity, but only in cortical collecting tubule. The effects of Li administration were different; it decreased Na-K-ATPase and H(+)-ATPase in both cortical collecting tubule and medullary collecting tubule. In cortical collecting tubule, the inhibitory effect on H(+)-ATPase activity was seen in vitro at a Li concentration similar to that found in urine. In contrast to the effect of Li on the H(+)-ATPase, in vitro Li stimulated Na-K-ATPase activity. These results suggest that the mechanism of action whereby these two agents result in distal renal tubular acidosis in humans and animals are different. In the collecting tubule, amiloride appears to act solely through a voltage-dependent mechanism by inhibiting cortical collecting tubule Na-K-ATPase. Li, by contrast, appears to have an additional effect in the cortical collecting tubule to inhibit the H(+)-ATPase. The biochemical differences seen with these drugs may explain the more severe acidemia universally found in animals after chronic Li administration.

Amiloride↗
PubMed1991

Calcium transport and extracellular pH in epithelial membranes.

Calcium plays a pivotal role in cell adhesion, ATPase function, and in membrane permeability. The molecular mechanism for these diverse actions include: hormonal factors, activation of intracellular mediators, and physical factors such as ionic mobility and pH. To further examine the effects of one physical factor, pH, we designed studies examining Ca transport in the isolated turtle bladder epithelium. This tissue is a high-resistance epithelium which reabsorbs Na and secretes H+. The turtle has only rudimentary parathyroid tissue, the gland does not respond to a lowered plasma Ca, and cyclic AMP is not a primary intracellular mediator. In a series of in vitro experiments, we examined Ca metabolism under conditions simulating metabolic acidosis and alkalosis. Acidosis markedly inhibited the mucosa-to-serosa Ca flux, while alkalosis stimulated it. The effect of acidosis on the mucosa-to-serosa Ca flux was independent of Na transport. Changing serosal pH had no effect on the serosa-to-mucosa Ca flux or on proton secretion. Total tissue Ca concentration, measured using atomic absorption spectrometry, was identical when the extracellular pH varied from 5.4 to 8.4. When epithelial cells were isolated and Ca uptake was measured over a wide pH range, a linear increase in uptake was seen as pH was increased from 4.4 to 8.4. In separated turtle bladder epithelial cells ATP-dependent Ca transport, in the mitochondrial-rich cells, was 4- to 5-fold higher than activity found in the granular cells. The mitochondrial-rich cells comprise approximately 20% of the total epithelial surface and are thought to be the cells primarily involved in proton secretion.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1991

Characterization of the N-ethylmaleimide-sensitive ATPase in rat cortical and medullary collecting tubule.

Hydrogen ion secretion in the kidney is thought to be mediated in part by an N-ethylmaleimide (NEM)-sensitive proton-translocating adenosine triphosphatase (ATPase). This enzyme has been found throughout the nephron, but it has not been completely characterized enzymatically in the rat collecting duct. In the present study we characterized the NEM-sensitive ATPase from microdissected cortical (CCT) and medullary (MCT) collecting tubules of the rat nephron. At optimum conditions, NEM-sensitive ATPase activity was the same in both tubule segments: activity was 275.6 +/- 18.6 pmol/mm/h in the CCT and 280.3 +/- 35.2 pmol/mm/h in the MCT (n = 23, NS). ATP sensitivity was greater in CCT than in MCT, and in the former guanosine triphosphate was able to partially support enzyme activity. Maximal enzyme inhibition with NEM occurred at a lower concentration in CCT as compared to MCT. At pH 7.0 in MCT enzyme activity was approximately one half that seen at pH 7.4; in MCT and CCT, the pH optimum was 7.4. The temperature optimum in both segments was between 37 and 42 degrees C. Enzyme activity in CCT and MCT was linear to 30 min and proportional to tubule length. These results demonstrate that there are important differences in the NEM-sensitive ATPase isolated from two segments of rat collecting duct, and raise the possibility that enzyme heterogeneity may exist.

Adenosine Triphosphatases↗
PubMed1990

Enzyme activity in obstructive uropathy: basis for salt wastage and the acidification defect.

Unilateral ureteral obstruction results in marked changes in renal function throughout the nephron, including impaired acid and potassium secretion and salt wastage. The nephron site believed responsible for the acidification defect is the collecting duct. It has been presumed, although not demonstrated, that the cellular mechanism for the acidification defect is both a decrease in transepithelial voltage and a decrease in activity of the proton pump located at the luminal membrane. The mechanism for the abnormalities in sodium handling are thought due to alterations in Na-K ATPase activity. Our laboratory has recently mapped the profile of the N-ethylmaleimide (NEM)-sensitive ATPase and Na-K ATPase in microdissected rat nephron, documenting their presence throughout much of the nephron. In animals with acute unilateral ureteral obstruction for 18 to 24 hours, we measured NEM-sensitive ATPase and Na-K ATPase activities in several nephron sites. In all nephron segments Na-K ATPase activity was markedly decreased. In the medullary collecting duct, NEM-sensitive ATPase activity was also markedly reduced in animals with acute ureteral obstruction; in the cortical collecting duct, activity fell significantly, but to a lesser degree than was observed in the medullary collecting duct. NEM-sensitive ATPase activity was unchanged from control in the proximal convoluted tubule and in the medullary thick ascending limb; in the cortical thick ascending limb enzyme activity increased. These results demonstrate a change in both Na-K ATPase and NEM-sensitive ATPase activities as a direct consequence of a defect known to result in salt wastage and an acidification defect in humans and animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphatases↗
PubMed1990

NEM-sensitive ATPase activity in rat nephron: effect of metabolic acidosis and alkalosis.

The present study was designed to quantitate the amount and to map the localization of N-ethylmaleimide (NEM)-sensitive adenosinetriphosphatase (ATPase) activity in microdissected segments of the rat nephron. After complete nephron mapping the effect of chronic metabolic acidosis and alkalosis on enzyme activity was determined. In control animals the highest enzyme activity was found in the early proximal convoluted tubule of juxtamedullary nephrons; superficial early proximal tubule as well as medullary and cortical thick ascending limbs and collecting ducts also contained substantial activity. Enzyme activity in the papillary collecting duct before entry into the ducts of Bellini was 329 +/- 93 pmol.mm-1.h-1 (n = 8); after entry, however, enzyme activity was approximately one-fourth that value (60 +/- 9 pmol.mm-1.h-1, n = 8, P less than 0.01). No NEM-sensitive ATPase activity was found in the thin limbs of the loop of Henle. Enzyme activity increased in both the medullary and cortical thick ascending limbs as well as in the cortical collecting tubule in response to NH4Cl-induced chronic metabolic acidosis; in the cortical collecting duct, metabolic acidosis increased maximum activity (Vmax) but did not change Michaelis-Menten constant (Km). In the proximal convoluted tubule, enzyme activity decreased with metabolic acidosis. Bicarbonate loading had no effect on enzyme activity except in the most distal portion of the collecting duct where it was stimulated. These results show that NEM-sensitive ATPase activity exists throughout much of the rat nephron. These data suggest that both the cortical collecting tubule and thick ascending limb are regulatory sites of distal urinary acidification during acid loading.

Acidosis↗
PubMed1989

Peculiar effects of temperature and polyvinylalcohol on the activity of bovine serum amine oxidase.

An inflexion point of enzyme activity at 38 - 42 degrees C of the bovine serum amineoxidase was found. This result, associated with non-strict Arrhenius curves and slightly different activation energies in various temperature intervals, suggests some conformational transitions at the mentioned temperatures. The high molecular weight polyvinylalcohol (100,000 Da) generated an activatory effect and a sigmoidal (non-Michaelis) curve of the dependence of the activity on the substrate concentrations, while the low molecular weight polyvinylalcohol (20,000 Da) does not produce this effect. The different ratio of the two types of polyvinylalcohol/enzyme monomer sizes is considered to be responsible for these different effects on the enzyme kinetics.

Amine Oxidase (Copper-Containing)↗
PubMed1989

Production of antibodies against the coenzyme pyrrolequinoline quinone.

Polyclonal antibodies against pyrrolequinoline quinone have been elicited in rabbits. These antibodies react with free and protein-bound pyrrolequinoline quinone. In particular they react with native and denatured lentil seedling amine oxidase as detected by dot-blot and ELISA assays. The presence of 1 mol pyrrolequinoline quinone per mol of enzyme was determined by the last method.

Amine Oxidase (Copper-Containing)↗
PubMed1989

Dimethyl sulfoxide affects water flow through a nonosmolar action.

Dimethyl sulfoxide (DMSO) is a dipolar organic compound commonly used as a solvent in studies of membrane transport. DMSO also has many effects on cell function and, although the precise mechanism of action is not known completely, it has been stated to exert its effect on transport solely through osmolality. The present study was designed to examine the effects of serosal DMSO at three osmolar concentrations on Basal Water Flow and vasopressin (AVP)- and cyclic AMP-stimulated water flow (Maximal Water Flow) in the toad bladder. The results obtained were compared to equi-osmolar concentrations of mannitol and NaCl. All three agents significantly enhanced Basal Water Flow after 60 min. The results obtained on Maximal Water Flow were different depending on the final osmolality. At 300 mOsm final concentration, all three agents increased AVP-stimulated water flow. When the serosal osmolality was 600 or 900 mOsm DMSO increased Maximal Water Flow, whereas mannitol and NaCl decreased it. When 300 mOsm DMSO plus 300 mOsm mannitol (600 mOsm total)-treated hemibladders were challenged with AVP, the water flow response was similar to that of 600 mOsm DMSO alone. In the presence of verapamil, AVP-stimulated water flow was decreased markedly; when DMSO was added to verapamil-pretreated hemibladders, and they were then challenged with AVP, water flow increased significantly. In similar experiments with mannitol, water flow remained inhibited. Dimethylsulfone did not enhance AVP-stimulated water flow as compared to the same concentration of DMSO. These results demonstrate that the effects of DMSO on water transport are not mediated solely by its osmolar action.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗