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S P Soltoff

Publications and source records attributed to S P Soltoff.

At least 55 records · Page 3Linked to original sources
PubMed1987

Extracellular ATP elevates intracellular free calcium in rat parotid acinar cells.

The effect of extracellular ATP on intracellular free Ca2+ was characterized in quin2-loaded parotid acinar cells. ATP specifically increased the intracellular Ca2+ concentration six-fold above a basal level of 180 nM. Of other purine nucleotides tested, only adenylylthiodiphosphate (ATP gamma S) had significant activity. ATP and the muscarinic agonist carbachol increased intracellular Ca2+ even in the absence of extracellular Ca2+. Both agonists stimulated K+ release, which was followed by reuptake of K+, even in the continued presence of agonist. In the absence of Mg2+, ATP was much more potent but no more efficacious in elevating intracellular Ca2+, suggesting that ATP4- is the active species. The effect of ATP was reversed by removal with hexokinase, arguing against a role for an active contaminant of ATP and against a non-specific permeabilizing effect of extracellular ATP. Lactate dehydrogenase release was unaffected by a maximally effective concentration of ATP. These observations are consistent with a possible neurotransmitter role for ATP in the rat parotid gland.

Adenosine Triphosphate↗
PubMed1987

Rapid desensitization of substance P- but not carbachol-induced increases in inositol trisphosphate and intracellular Ca++ in rat parotid acinar cells.

The effects of supramaximal concentrations of substance P and the cholinergic agonist carbachol on the accumulation of inositol trisphosphate and the elevation of the intracellular free calcium concentration were compared in rat parotid acinar cells. Substance P was fully as effective as carbachol at initial times, but there was a rapid loss of the substance P responses while the effects of carbachol were well maintained. The loss of the substance P responses represented desensitization rather than degradation of the peptide since further additions of substance P were without effect. Desensitization to substance P did not involve long-term loss of substance P receptors as it was fully reversible in less than twenty minutes, the minimum time to extensively wash previously desensitized cells.

Animals↗
PubMed1986

Potassium transport in the rabbit renal proximal tubule: effects of barium, ouabain, valinomycin, and other ionophores.

Potassium fluxes in a suspension of rabbit proximal tubules were monitored using a potassium-sensitive extracellular electrode. Ouabain (10(-4) M) and barium (5 mM) were used to selectively quantitate the potassium efflux pathway (105 +/- 5 nmol K+ X mg protein-1 X min-1) and the sodium pump-related potassium influx (108 +/- 7), respectively. These equal and opposite fluxes suggest that potassium accumulation in the cell occurs mainly through the sodium pump and that potassium efflux occurs mainly through barium-sensitive potassium channels. Thus the activity of the sodium pump (Na,K-ATPase) in the basolateral membrane of the proximal tubule is balanced by the efflux of potassium, presumably across the basolateral membrane, which has a high potassium permeability. In addition, the effect of valinomycin and other ionophores was examined on potassium fluxes and several metabolic parameters [oxygen consumption (QO2), ATP content]. The addition of valinomycin to the tubules produced a net efflux of potassium which was quantitatively equivalent to the efflux produced by the addition of ouabain. The valinomycin-induced efflux was mainly due to the activity of valinomycin as a mitochondrial uncoupler, which indirectly inhibited the sodium pump by allowing a rapid reduction of the intracellular ATP. Amphotericin, nystatin, and monensin all produced large net releases of intracellular potassium. The action of the ionophores could be localized to the plasma or mitochondrial membrane and classified into three groups, as follows: those which demonstrated full mitochondrial uncoupler activity (FCCP, valinomycin), those which had no uncoupler activity (amphotericin B, nystatin); and those which displayed partial uncoupler activity (monensin, nigericin).

Animals↗
PubMed1986

Amiloride analogues inhibit proximal tubule metabolism.

The effects of two amiloride analogues, ethylisopropylamiloride and methylisopropylamiloride, were tested on active Na+ transport and oxidative metabolism of a rabbit proximal renal tubule suspension. These two analogues have been recently reported to inhibit Na+-H+ antiport activity of various tissues with greater potency than amiloride. In proximal tubules, no effects were detected at concentrations less than 10(-4) M. At concentrations greater than 10(-4) M, both of these compounds inhibited the ouabain-sensitive O2 consumption (a direct measure of Na+ pump activity) with a greater potency than amiloride. Investigations into possible metabolic effects revealed that both amiloride analogues inhibited mitochondrial production of ATP at these concentrations, whereas amiloride did not directly affect metabolism. The amiloride analogues inhibited the nystatin-stimulated O2 consumption (which measures Na+-K+-ATPase activity in the intact cells) as well as the ATP content. These results suggest that the primary effects of these analogues on rabbit proximal tubules are to inhibit both the Na+-K+-ATPase and oxidative metabolism.

Adenine Nucleotides↗
PubMed1985

Intracellular respiratory dysfunction and cell injury in short-term anoxia of rabbit renal proximal tubules.

The effects of short-term anoxia and hypoxia were studied in a rabbit proximal renal tubule suspension in order to avoid the hemodynamic consequences of clamp-induced ischemia. The suspension was subjected to anoxia for 10-40 min and the effects on a number of cellular transport and respiratory parameters were monitored. Cellular respiration was measured upon addition of nystatin (Nys) to maximally stimulate Na pump activity. Mitochondrial respiration was measured in the tubules by addition of digitonin and ADP to obtain the state 3 respiratory rate. The release of lactate dehydrogenase (LDH) was measured as an index of plasma membrane damage. The cellular contents of K and Ca were also measured. Results show that 10 and 20 min of anoxia partially inhibited Nys-stimulated and mitochondrial respiration, and partially decreased the K contents, but all these effects were largely reversible after 20 min of reoxygenation. After 40 min of anoxia and 20 min of reoxygenation, all these variables remained irreversibly inhibited: Nys-stimulated respiration by 54%, mitochondrial respiration by 50%, K content by 42%, and LDH release was 40% of total. Ca content decreased slightly during anoxia, but increased up to fourfold during severe hypoxia; the excess Ca was released during the first 10 min of reoxygenation. The degree of respiratory impairment was identical during anoxia or hypoxia, suggesting that Ca accumulation was not associated with the impairment. Decreasing the extracellular Ca to 2.5 microM decreased LDH release significantly during anoxia, suggesting that plasma membrane damage during anoxia may be associated with increased intracellular free Ca. Addition of Mg-adenosine triphosphate during anoxia dramatically improved recovery of all the measured parameters after the anoxic period.

Adenosine Triphosphate↗
PubMed1984

Active ion transport in the renal proximal tubule. I. Transport and metabolic studies.

Various aspects of the interrelationship between ion transport and cellular metabolism were investigated using a suspension of rabbit cortical tubules that were mainly proximal in nature. Using the intact tubules, the compartmentation of K within the renal cell was studied by performing 42K uptake studies. The oxygen consumption (QO2) of the tubules was measured under similar conditions, as well as when the Na pump was stimulated by increasing Na+ entry with nystatin. In addition, the state 3 rate of respiration was measured when the mitochondria of digitonin-permeabilized tubules were stimulated by ADP. At 37 and 25 degrees C, a single-compartmental uptake of 42K was observed, which suggests that extracellular K+ communicates with a single compartment within the renal cell. Between 37 and 15 degrees C, the ouabain-sensitive QO2 and the initial 42K uptake rate were parallel in an Arrhenius-type plot, which indicated that active ion transport and oxidative phosphorylation remain tightly coupled within this temperature range. At all temperatures between 37 and 15 degrees C, nystatin stimulated the QO2, which demonstrates that the entry of Na+ into the renal cells was rate limiting for active Na+ transport throughout this temperature range. Between 37 and 20 degrees C, the nystatin-stimulated QO2 was nearly equal to the state 3 rate of respiration, which suggests that active ion transport may be limited by ATP availability under these conditions. At 15 degrees C, nystatin addition stimulated the QO2 well below the state 3 respiratory rate.

Animals↗
PubMed1984

Active ion transport in the renal proximal tubule. II. Ionic dependence of the Na pump.

The dependence of Na pump activity on intracellular and extracellular Na+ and K+ was investigated using a suspension of rabbit cortical tubules that contained mostly (86%) proximal tubules. The ouabain-sensitive rate of respiration (QO2) was used to measure the Na pump activity of intact tubules, and the Na,K-ATPase hydrolytic activity was measured using lysed proximal tubule membranes. The dependence (K0.5) of the Na pump on intracellular Na+ was affected by the relative intracellular concentration of K+, ranging from approximately 10 to 15 mM at low K+ and increasing to approximately 30 mM as the intracellular K+ was increased. The Na pump had a K0.5 for extracellular K+ of 1.3 mM in the presence of saturating concentrations of intracellular Na+. Measurements of the Na,K-ATPase activity under comparable conditions rendered similar values for the K0.5 of Na+ and K+. The Na pump activity in the intact tubules saturated as a function of extracellular Na at approximately 80 mM Na, with a K0.5 of 30 mM. Since Na pump activity under these conditions could be further stimulated by increasing Na+ entry with the cationophore nystatin, these values pertain to the Na+ entry step and not to the Na+ dependence of the intracellular Na+ site. When tubules were exposed to different extracellular K+ concentrations and the intracellular Na+ concentration was subsaturating, the Na pump had an apparent K0.5 of 0.4 mM for extracellular K. Under normal physiological conditions, the Na pump is unsaturated with respect to intracellular Na+, and indirect analysis suggests that the proximal cell may have an intracellular Na+ concentration of approximately 35 mM.

Animals↗
PubMed1984

Active ion transport in the renal proximal tubule. III. The ATP dependence of the Na pump.

The dependence of the Na pump activity of intact renal tubules on the ATP concentration was investigated using a suspension of rabbit cortical tubules. Rotenone (an inhibitor of mitochondrial oxidative phosphorylation) was used in graded fashion to alter the cellular ATP, and the Na pump activity was measured when the pump was stimulated by adding KCl to tubules suspended in a K+-free medium. The K+ uptake into the tubule was measured using an extracellular K+ electrode, and the oxygen consumption (QO2) was measured using a Clark-type oxygen electrode. The Na pump activity was found to have a linear, nonsaturating dependence on the ATP concentration. However, the Na,K-ATPase hydrolytic activity (assayed biochemically) of lysed proximal tubule membranes demonstrated saturation and had a K0.5 value of 0.4 mM ATP. Presumably, unknown cytosolic factors present in the intact renal cell but not normally present in the biochemical assay accounted for the differences between the two measurements. The data suggest that an alteration in the intracellular ATP will result in a proportional change in active ion transport activity. Moreover, additional findings also suggest that the basal (non-transport-related) QO2 may be redirected to support the proximal Na pump activity when transport activity is stressed. Thus, basal respiration is not invariant under all conditions, and ion transport activity appears to be maintained foremost among cellular ATP-dependent processes.

Adenosine Triphosphate↗
PubMed1984

Interactions between phosphate and oxidative metabolism in proximal renal tubules.

These studies examine the phosphate dependence of fluid absorption and oxidative metabolism in proximal tubules from rabbit kidney. Removal of inorganic phosphate from intraluminal fluid in isolated perfused tubules reduced fluid absorption (Jv) from 1.0 nl X mm-1 X min-1 to zero and removal of phosphate from the medium bathing tubules in suspension reduced O2 consumption rates (coupled, uncoupled, ouabain sensitive, and ouabain insensitive) and ATP contents by 30-40%. Inhibitions induced by removal of phosphate could be altered by addition of selected organic substrates to ambient fluids. Addition of succinate, citrate, or malate preserved uncoupled respiration and partially preserved Jv (0.4-0.9 nl X mm-1 X min-1), with succinate being most effective. Addition of short-chain fatty acids (butyrate or valerate) to phosphate-free media had little or no effect on Jv. n-Butylmalonate, an inhibitor of dicarboxylate anion transport into mitochondria, reduced oxidative metabolism, ATP content, and Jv when added to phosphate-containing media but had no further effect on these tubular functions when added to phosphate-free media. Together these results suggest that phosphate limitation reduces dicarboxylate anion availability to mitochondria and that this inhibition may contribute to the overall reduction in oxidative metabolism and Jv observed under these conditions.

Adenosine Triphosphate↗
PubMed1983

Amiloride directly inhibits the Na,K-ATPase activity of rabbit kidney proximal tubules.

Amiloride inhibited the ouabain-sensitive rate of oxygen consumption (QO2) of a suspension of rabbit intact proximal tubules in the presence of different concentrations of extracellular sodium. Measurements of the ouabain-sensitive QO2 in the presence of nystatin, the tissue sodium and potassium contents of the tubules in suspension, and the sodium- and potassium-dependent adenosinetriphosphatase (Na,K-ATPase) activity of lysed tubule membranes indicated that the effect of amiloride was due to a direct inhibition of the Na,K-ATPase activity of the proximal tubule.

Amiloride↗
PubMed1982

Metabolic inhibitors: effects on metabolism and transport in the proximal tubule.

This study examined the effects of the metabolic inhibitors rotenone and antimycin A on oxidative metabolism and transport in the proximal renal tubule of the rabbit. Measurements of oxygen consumption rate (QO2), cellular ATP content, and mitochondrial NAD redox state were made in suspensions of renal cortical tubules. Parallel experiments were conducted in isolated perfused proximal convoluted tubules to measure the absorption rates of fluid (Jv), phosphate (JlbPO4), and glucose (JlbGlc). The results indicate that rotenone and antimycin A, at doses (10(-6) M) that maximally inhibited mitochondrial oxidative phosphorylation, abolished net fluid and phosphate absorption and nearly eliminated net glucose transport. Partial inhibition of oxidative metabolism with 10(-7) M rotenone caused proportional reductions in QO2, ATP content, and Jv; however, JlbPO4 was reduced more markedly than either Jv or JlbGlc. We conclude that rotenone and antimycin A inhibit the sodium-dependent transport of fluid, phosphate, and glucose by blocking mitochondrial ATP production. Furthermore, the inhibition of mitochondrial oxidative metabolism and the inhibition of net sodium transport are closely correlated.

Adenosine Triphosphate↗
PubMed1980

Coupling of active ion transport and aerobic respiratory rate in isolated renal tubules.

We report the results of studies in which the cytoplasmic coupling between Na+,K+-ATPase activity (presumably a measure of active transport) and the mitochondrial respiratory rate was investigated in a tubule suspension from the rabbit kidney cortex. Simultaneous measurements of the redox state of mitochondrial nicotinamide adenine dinucleotide (NAD) (performed fluorometrically), the cellular ATP and ADP concentrations, and the oxygen consumption rate (QO2) were made under conditions known to alter the Na+,K+-ATPase turnover. Ouabain (25 microM) caused: (i) a 54% inhibition of QO2, (ii) a net reduction of NAD, and (iii) a 30% increase in the ATP/ADP ratio. The addition of K+ (5 ?M) to K+-depleted tubules caused: (i) an initial 127% stimulation of QO2 followed by a new steady-state QO2 50% above control, (ii) an initial large oxidation of NAD followed by a new steady state more oxidized than the control level, and (iii) a 47% decrease in the cellular ATP/ADP ratio. These data indicate that the cellular ATP and ADP concentrations or the ATP/ADP ratio may be part of the coupling mechanism linking Na+,K+-ATPase turnover and the aerobic metabolic rate in kidney.

Adenosine Diphosphate↗
PubMed1980

Improved renal cortical tubule suspension: spectrophotometric study of O2 delivery.

An improved cortical tubule suspension from the rabbit kidney is described that contains almost entirely proximal convoluted tubules with little contamination by cellular debris or glomeruli. These tubules appear to be capable of active transepithelial transport, since their tubular lumina are open and ouabain inhibits 70% of the QO2. In previous preparations with closed tubular lumina, ouabain inhibited QO2 only 40% and the base-line QO2 was one-half to one-quarter that of the present preparation. The delivery of oxygen to this tubule suspension was compared to that of slices by three different means: oxygen consumption kinetics, ATP content, and, more directly by spectrophotometric monitoring of the redox state of cytochrome oxidase. Results demonstrate that the cortical slice is evidently oxygen deficient even when the bath PO2 is in excess of 570 mmHg. In contrast, the tubule suspension is shown to be adequately oxygenated even at a bath PO2 of 10 mmHg. This tubule suspension will be highly applicable for the analysis of aerobic metabolism in a functionally intact renal preparation by optical, electrode, and biochemical assay technologies.

Adenosine Triphosphate↗