Omission Of Sodium Research Articles

Management of Recipients With Hyponatremia During and After Liver Transplantation; Ten Year Experience of Single Center.

A.Hyponatemia is frequently found in recipients of liver transplantation (LT) and a known risk factor for specific neurologic complication, central pontine myelinolysis (CPM). Although usually recommended rate of sodium increase is ≤ 10mEq/L/d, there was no proven method of safe correction. Since there were few reports about the management of hyponatremia in LT, we report our results of ten year period. B. With IRB approval, consecutive 1000 LT recipients from December 2004 to July 2013 were retrospectively reviewed. We tried to maintain preoperative sodium level during LT with half saline, and after LT with omission of sodium in main fluid and drug mix fluid until recipients started oral intake. C.Fifty-three adult LT recipients had preoperative hyponatremia (≤ 125 mEq/L). Characteristics of recipients with hyponatremia were age 50.6 ± 9.8 years, gender ratio (male 81.1%), body weight 63.7 ± 11.9 kg, MELD score 27.7 ± 10.9, graft type (living 38 vs deceased 15 patients) and indication of LT (HBV 33, HCV 10, Alcoholic 6, Others 4 patients). Although large amounts of isotonic saline-based solutions and blood products (10,326 ± 3,872 ml) were administered intraoperatively, sodium change during LT was 6.1 ± 3.3 mEq/L, and intraoperative sodium increase > 10mEq/L was observed in 3 recipients. Oral intake was started at postoperative day (POD) 6.1 ± 2.5, and sodium change until oral intake was 9.7 ± 6.3 mEq/L. Three recipients with sodium increase > 10mEq/L within 24 h period including LT operation time did not develop neurological manifestations suggesting CPM. In contrast, magnetic resonance imaging (MRI) findings suggestive of CPM were detected in 3 other recipients. But, daily sodium increase was less than 10mEq/L and the reason for MRI examination was nonspecific (headache, tremor, and rigidity). D. In spite of our effort, we couldn't completely maintain preoperative sodium level. Vigilant monitoring of sodium level is strongly recommended to decrease the risk of CPM in LT recipients with hyponatremia.

Non-invasive single cell pH measurements in the isolated perfused pancreas.

1. A new method was developed for non-invasive investigations of intracellular pH (pHi) regulation in different cell types of the isolated perfused pancreas using a confocal laser scanning technique. 2. After removal of the rat pancreas the coeliac artery was cannulated and the splenic segment of the pancreas was perfused with dextran (5%)-Ringer solution at a constant flow rate of 2 mL/min. In a temperature-controlled (37 degrees C) chamber, pH regulation was studied using the pH-sensitive fluorescent dye 2',7'-bis-(2-carboxyethyl)-5-(-6)-carboxyfluorescein (BCECF) with a confocal microscope (MRC-600; Bio-Rad, Hercules, CA, USA). 3. Image analysis permitted the identification and comparison of different cell types with a pHi of 7.26+/-0.1 in acinar cells and of 7.02+/-0.1 in endothelial cells. Increasing PCO2 from 5 to 20% resulted in a rapid decrease in pHi. Omission of sodium from the perfusate resulted in a smooth decline in pHi. Both decreases were found to be fully reversible. Increasing PCO2 under sodium-free conditions also resulted in a drop of pHi that was, however, not fully reversible, suggesting involvement of the Na+/H+ exchanger in the regulation of pHi in the intact organ. 4. The above method completely preserves tissue integrity and, therefore, allows the study of pH regulation in different cell types of the pancreas simultaneously and without interference with their functional arrangement. The technique should be of specific value to investigate experimental disease states of the pancreas.

The mechanism underlying the laxative properties of parsley extract.

Parsley has been claimed in folk medicine to possess laxative properties attributed to the presence therein of some volatile oils that are more concentrated in seeds than in stems or leaves. The advocated physiological effect of parsley, does not have, however, any proven scientific background and relies mainly on simple observations and empirical information. This work aims at providing the scientific evidence that would confirm or reject the claimed laxative role of parsley, and at determining its mechanism of action if present. A perfusion technique was used to measure the net fluid absorption from the rat colon. The addition of an aqueous extract of parsley seeds to the perfusion buffer, and the omission of sodium, both reduced significantly net water absorption from the colon, as compared to the control. Parsley, added to a sodium-free buffer did not lead to any further significant change in water absorption as compared to parsley alone inferring that with parsley sodium absorption was already inhibited. Since K+ and Cl- secretion depends on the activity of the NaKCl2 transporter, the latter was inhibited with furosemide which increased significantly net water absorption. When parsley and furosemide were added together, net water absorption was significantly higher than with parsley alone and significantly lower than with furosemide alone. In addition, parsley extract was shown to inhibit the in vitro activity of the Na+-K+ATPase in a colon homogenate and the activity of a partially purified dog kidney ATPase. The results suggest that parsley acts by, inhibiting sodium and consequently water absorption through an inhibition of the Na+-K+ pump, and by stimulating the NaKCl, transporter and increasing electrolyte and water secretion.

3H]TYRAMINE UPTAKE BY RAT LIVER SLICES

Rat liver slices were employed as experimental model to characterise the system involved in the transport process which participates in liver tyramine uptake. The uptake of 0.4 μmol l−1of [3H]tyramine by rat liver slices was linear from 5 min up to the end of incubation. At 15 min the uptake was 4.58±0.18 pmol mg−1protein. The accumulation of [3H]tyramine was sensitive to temperature (69.3±4.0% inhibition at 0°C, P<0.001), to sodium omission replaced by 150 mmol l−1Tris or 110 mmol l−1Tris+40 mmol l−1choline (27.6±6.0%,P <0.01, and 24.6±3.8% inhibition, P<0.01, respectively), and the inhibition of Na+–K+-adenosine triphosphatase by 150 μmol l−1ouabain (20.4±2.6% decrease, P<0.01). Uptake of [3H]tyramine was cocaine- (10 μmol l−1) and desipramine- (1 μmol l−1) dependent (32.2±6.4%, P<0.05, and 31.6±4.0% inhibition,P <0.05, respectively). Uptake of [3H]tyramine in rat liver slices was not modified by 30 μmol l−1isoprenaline, 30 μmol l−1corticosterone, 30 μmol l−1normetanephrine and noradrenaline up to 4 μm ; at higher noradrenaline concentrations tyramine transport was diminished (P<0.05). Results achieved by incubation with increasing tyramine concentrations indicate that at the micromolar level hepatic uptake occurs by a combined passive diffusion and transport-mediated mechanism, whereas at greater tyramine concentrations passive transport predominates. These results suggest that both simple diffusion and a transport-mediated mechanism are involved in this uptake from hepatocytes, which presents features similar to those described for type 1 non-neuronal uptake systems. 1999 Academic Press@p$hr

Efficient hepatic uptake and concentrative biliary excretion of a mercapturic acid.

The role of the liver in the disposition of circulating mercapturic acids was examined in anesthetized rats and in the isolated perfused rat liver using S-2,4-dinitrophenyl-N-acetylcysteine (DNP-NAC) as the model compound. When DNP-NAC was infused into the jugular vein (150 or 600 nmol over 60 min) it was rapidly and nearly quantitatively excreted as DNP-NAC into bile (42-36% of the dose) and urine (48-62% of dose). Some minor metabolites were detected in bile (<4%), with the major metabolite coeluting on HPLC with the DNP conjugate of glutathione (DNP-SG). Isolated rat livers perfused single pass with 3 microM DNP-NAC removed 72 +/- 9% of this mercapturic acid from perfusate. This rapid DNP-NAC uptake was unaffected by sodium omission, or by L-cysteine, L-glutamate, L-cystine, or N-acetylated amino acids, but was decreased by inhibitors of hepatic sinusoidal organic anion transporters (oatp), indicating that DNP-NAC is a substrate for these transporters. The DNP-NAC removed from perfusate was promptly excreted into bile, eliciting a dose-dependent choleresis. DNP-NAC itself constituted approximately 75% of the total dose recovered in bile, reaching a concentration of 9 mM when livers were perfused in a recirculating mode with an initial DNP-NAC concentration of 250 microM. Other biliary metabolites included DNP-SG, DNP-cysteinylglycine, and DNP-cysteine. DNP-SG was likely formed by a spontaneous retro-Michael reaction between glutathione and DNP-NAC. Subsequent degradation of DNP-SG by biliary gamma-glutamyltranspeptidase and dipeptidase activities accounts for the cysteinylglycine and cysteine conjugates, respectively. These findings indicate the presence of efficient hepatic mechanisms for sinusoidal uptake and biliary excretion of circulating mercapturic acids in rat liver and demonstrate that the liver plays a role in their whole body elimination.

Effect of hypoxia on force, intracellular pH and Ca2+ concentration in rat cerebral and mesenteric small arteries.

1. The effect of severe hypoxia on force, intracellular Ca2+ concentration ([Ca2+]i) and pHi was studied in isolated small arteries from rat brain and rat mesenterium. The arteries were mounted for isometric force recording while [Ca2+]i was measured with fura-2 or pHi was measured with bis-carboxyethylcarboxyfluorescein (BCECF). 2. Hypoxia reduced the force development in response to arginine vasopressin (AVP) while [Ca2+]i was unchanged or only slightly reduced. Inhibition of acid extrusion by omission of sodium caused no force development in mesenteric arteries, but the fall in pHi was enhanced during hypoxia. In cerebral arteries, hypoxia reduced the force development associated with omission of sodium, and the fall in pHi was less than during normoxic conditions. When acid extrusion was intact, pHi was not affected by hypoxia and the changes in pHi during activation with AVP were similar during hypoxia and in the control situation. 3. Although a decrease in smooth muscle [Ca2+]i may be partly responsible for the reduced force development during hypoxia, [Ca2+]i-independent mechanism(s) may play an even more important role. Furthermore, although hypoxia and force development are associated with enhanced acid production, acid extrusion maintains pHi near the control level and it is unlikely that a decrease in smooth muscle pHi plays any role in the reduced force development during hypoxia.

Atrial natriuretic factor modifies noradrenaline release in a sodium-free medium.

1. The effects of atrial natriuretic factor (ANF) on 3H-noradrenaline (3H-NA) release evoked by a sodium-free medium (SFM) were studied. The experiments were carried out in rat hypothalamic slices incubated in vitro. 2. ANF (1, 10 and 100 nM) decreased NA release evoked by the omission of sodium in a concentration-dependent way. When calcium was omitted from a SFM, NA output was partially diminished. However, if ANF was added to the SFM/calcium free medium NA secretion showed no modifications. 3. Present results suggest that, in rat hypothalamus, NA release evoked by Na+ omission is divided into two fractions: one independent of and the other dependent on extracellular calcium. In addition, ANF modifies NA release evoked by SFM dependent on extracellular calcium.

Sodium inhibits hormone release and stimulates calcium efflux from isolated nerve endings of the rat neurohypophysis.

1. We studied the effects of extracellular sodium on the secretion of vasopressin (VP) and oxytocin (OT) and the efflux of 45Ca from isolated, perfused nerve endings of the rat neurohypophysis (neurosecretosomes). 2. Upon removal of sodium from the perfusing medium, basal release of VP and OT increased by 3.95 +/- 0.23- and 3.71 +/- 0.22-fold, respectively, followed by a decline to about double the levels in normal (150 mM) sodium (P less than or equal to 0.1). 3. Compared to neurosecretosomes perfused in normal (150 mM) sodium, omission of sodium from the medium augmented ionomycin-induced VP and OT secretion by 66 +/- 5- and 20 +/- 3-fold, respectively, and A23187-induced secretion was increased 1.3 +/- 0.4- and 1.3 +/- 0.1-fold (P less than or equal to 0.01 for both ionophores). 4. The inhibition of ionomycin-induced secretion by sodium was concentration dependent (P less than or equal to 0.01 for sodium greater than or equal to 5 mM); the IC50 was about 10 mM sodium for both hormones, and the Hill slope was close to -1. 5. The rate of 45Ca efflux from neurosecretosomes showed 2.7 +/- 0.1-fold stimulation upon increasing sodium from 4.5 to 150 mM (P less than or equal to 0.01). 6. Our results suggest that sodium inhibits basal and stimulated secretion at the nerve terminal, possibly by reducing intraterminal calcium through sodium/calcium exchange.

Neuronal Glutamine Utilization: Glutamine/Glutamate Homeostasis in Synaptosomes

The synaptosomal metabolism of glutamine was studied under in vitro conditions that simulate depolarization in vivo. With [2-15N]glutamine as precursor, the [glutamine]i was diminished in the presence of veratridine or 50 mM KCl, but the total amounts of [15N]glutamate and [15N]aspartate formed were either equal to those of control incubations (veratridine) or higher (50 mM [KCl]). This suggests that depolarization decreases glutamine uptake and independently augments glutaminase activity. Omission of sodium from the medium was associated with low internal levels of glutamine which indicates that influx occurs as a charged Na(+)-amino acid complex. It is postulated that a reduction in membrane potential and a collapse of the Na+ gradient decrease the driving forces for glutamine accumulation and thus inhibit its uptake and enhance its release under depolarizing conditions. Inorganic phosphate stimulated glutaminase activity, particularly in the presence of calcium. At 2 mM or lower [phosphate] in the medium, calcium inhibited glutamine utilization and the production of glutamate, aspartate, and ammonia from glutamine. At a high (10 mM) medium [phosphate], calcium stimulated glutamine catabolism. It is suggested that a veratridine-induced increase in intrasynaptosomal inorganic phosphate is responsible for the enhancement of flux through glutaminase; calcium affects glutaminase indirectly by modulating the level of free intramitochondrial [phosphate]. Because phosphate also lowers the Km of glutaminase for glutamine, augmentation of the amino acid breakdown may occur even when depolarization lowers [glutamine]i. Reducing the intrasynaptosomal glutamate to 26 nmol/mg of protein had little effect on glutamine catabolism, but raising the pH to 7.9 markedly increased formation of glutamate and aspartate. It is concluded that phosphate and H+ are the major physiologic regulators of glutaminase activity.

Sodium entry routes in principal and intercalated cells of the isolated perfused cortical collecting duct

Transmembrane sodium transport pathways were studied in principal and intercalated cells of the isolated perfused rabbit cortical collecting duct. Intracellular electrolyte concentrations in individual collecting duct cells were measured by electron microprobe analysis during blockage of basolateral Na-K-ATPase by ouabain and simultaneous inhibition of sodium entry across the apical and/or basolateral cell membrane. In principal cells the ouabain-induced rise in cell sodium concentration could only partially be blocked by amiloride (10(-4) mol/l) in the perfusion fluid. Amiloride (10(-3) mol/l) added to the bathing solution produced a further, significant reduction of sodium influx. In principal cells the ouabain-induced increase in sodium concentration was completely prevented by amiloride in the perfusion solution in combination with omission of sodium from the peritubular bathing solution. In intercalated cells ouabain caused a less pronounced increase in sodium concentration than in principal cells. Neither amiloride in the perfusate, nor amiloride in both bathing and perfusion solution, significantly reduced the ouabain-induced rise in intercalated cell sodium concentration. These results indicate that in principal cells amiloride-sensitive sodium channels constitute the predominant pathway for sodium entry across the apical cell membrane. In addition, substantial amounts of sodium enter principal cells across the basolateral cell membrane, probably via Na-H exchange. Finally, the data suggest that in intercalated cells sodium channels and the Na-H exchange are sparse or even absent.

The influence of sodium omission on α2-adrenergic inhibition of insulin release by mouse islets

The mechanisms by which activation of α 2-adrenoceptors inhibits insulin release are still incompletely understood. This study, performed with isolated mouse islets, identifies a possible role of Na + in this inhibition. Regardless of the stimulus used to induce insulin release, the inhibitory effect of low concentrations of clonidine (0.02–0.1 μM) was markedly smaller in the absence of Na + (with choline or lithium as substitute) than in its presence. The effectiveness of a high concentration of clonidine (1 μM) was, however, not affected by Na + omission. The results indicate either that Na + omission indirectly counteracts an effect of clonidine (e.g. on a membrane permeability or on Ca 2+ handling), or that Na + is directly involved in or on Ca 2+ handling), or that Na + is directly involved in a cellular process (e.g. a Na + current or the Na +/H + exchange) controlled by α 2-adrenoceptors.

Effects of acute sodium omission on insulin release, ionic flux and membrane potential in mouse pancreatic B-cells

The effects of acute omission of extracellular Na + on pancreatic B-cell function were studied in mouse islets, using choline and lithium salts as impermeant and permeant substitutes, respectively. In the absence of glucose, choline substitution for Na + hyperpolarized the B-cell membrane, inhibited 86Rb + and 45Ca 2+ efflux, but did not affect insulin release. In contrast, Li + substitution for Na + depolarized the B-cell membrane and caused a Ca 2+-independent, transient acceleration of 45Ca 2+ efflux and insulin release. Na + replacement by choline in the presence of 10 mM glucose and 2.5 mM Ca 2+ again rapidly hyperpolarized the B-cell membrane. This hyperpolarization was then followed by a phase of depolarization with continuous spike activity, before long slow waves of the membrane potential resumed. Under these conditions, 86Rb + efflux first decreased before accelerating, concomitantly with marked and parallel increases in 45Ca 2+ efflux and insulin release. In the absence of Ca 2+, 45Ca 2+ and 86Rb + efflux were inhibited and insulin release was unaffected by choline substitution for Na +. Na + replacement by Li + in the presence of 10 mM glucose rapidly depolarized the B-cell membrane, caused an intense continuous spike activity, and accelerated 45Ca 2+ efflux, 86Rb + efflux and insulin release. In the absence of extracellular Ca 2+, Li + still caused a rapid but transient increase in 45Ca 2+ and 86Rb + efflux and in insulin release. Although not indispensable for insulin release, Na + plays an important regulatory role in stimulus-secretion coupling by modulating, among others, membrane potential and ionic fluxes in B-cells.

Na +/H + exchange and aggregation of human platelets activated by ADP: the exchange is not required for aggregation

Isolated human blood platelets, loaded with the pH-sensitive fluorescence dye 2′,7′-bis(carboxyethyl)-5,6-carboxyfluorescein show cytoplasmic alkalinization upon stimulation with thrombin but acidification with ADP stimulation. In both cases a Na +/H + exchange is activated. This can be revealed by sensitivity of the induced pH changes to amiloride and to 5-N-(3- aminophenyl)amiloride (APA), known inhibitors of the Na +/H + exchanger, and by a dependence on sodium in the external medium. ADP-induced platelet aggregation is not affected by omission of sodium from the external medium. Furthermore, aggregation is barely inhibited (less than 10%) by amiloride or APA at concentrations up to 50 μM while the K i values in affecting the Na +/H + exchange are 5.9 and 1.6 μM for amiloride and APA, respectively. Platelet apparently due to a secondary effect of the agents. It is concluded that platelet aggregation induced by ADP is not dependent on activation of Na +/H + exchange.

Ionic mechanisms implicated in the stimulation of cerebellar cyclic GMP levels by N-methyl-D-aspartate.

N-Methyl-D-aspartate (NMDA) increases cyclic GMP levels in immature rat cerebellar slices incubated in magnesium-containing Krebs buffer in vitro. This effect is blocked by 2-amino-5-phosphonovalerate and by D-alpha-aminoadipate, but not by glutamic acid diethyl ester or gamma-D-glutamylaminomethylsulfonic acid, indicating specific involvement of the NMDA receptor. The response produced by NMDA is abolished by removal of calcium from the medium, proportional to the concentration of extracellular calcium, and blocked by a number of inorganic (Ni2+, Co2+, Cd2+, La3+, Mn2+) calcium antagonists. The responses to NMDA are not blocked by barium or strontium and persist when these ions are substituted for calcium in the incubation medium. The effects of NMDA are blocked by, but are not particularly sensitive to, the organic voltage-dependent calcium channel antagonists. Nifedipine (10 microM) produces partial inhibition of the effects of NMDA, which are also antagonized by high (greater than 200 microM) concentrations of diltiazem and verapamil. The effects of NMDA are tetrodotoxin insensitive but are abolished by omission of sodium from the medium and inhibited by a tetrodotoxin-insensitive sodium channel blocker, Zn2+. The results suggest that calcium channel opening is a consequence of NMDA receptor activation in this model. However, the sodium dependence of the response argues against the use of receptor-operated calcium channels, whereas the weak activity of the organic voltage-sensitive calcium channel antagonists argues either against the use of voltage-dependent calcium channels, or that those implicated in the effects of NMDA are insensitive to these agents.(ABSTRACT TRUNCATED AT 250 WORDS)

Origin of transport inhibition after omission of serosal sodium.

The omission of sodium from the serosal incubation fluid in isolated frog skins inhibits transcellular Na transport. By the use of intracellular recording with microelectrodes, it has been demonstrated that this inhibition is associated with an increase of the basolateral membrane resistance, resulting in a depolarization of the short-circuited cells. This depolarization in turn accounts for the reduction of Na entry across the apical border. The resistance changes across the outer (apical) border are small in magnitude and unrelated to the inhibition of transcellular transport. The origin of the increase in basolateral membrane resistance, presumably due to decrease of K permeability, is unclear. These data do not support the hypothesis that intracellular Ca regulates the resistance of the apical and basolateral membranes.

Taurocholate uptake by isolated skate hepatocytes: effect of albumin.

Taurocholate transport was analyzed in a well characterized, polarized hepatocyte preparation from the small skate (Raja erinacea), an analbuminemic species that does not synthesize bile acids. In addition, the effect of sodium omission, bovine albumin, ovalbumin, and bovine gamma-globulin on the uptake of taurocholate was studied. Uptake could be divided into nonsaturable (0.48 pmol X min-1 X mg protein-1. microM-1) and saturable components (Km, 32.5 microM and Vmax 110 pmol X min-1 X mg protein-1). No evidence for sodium dependence could be obtained. Glycocholate competitively inhibited taurocholate uptake. The initial rate of taurocholate uptake was also inhibited by sulfobromophthalein, N-(4-azido-2-nitrophenyl)-2-aminoethyl sulfonate, and 4,4'-diisothiocyanostylbene-2,2'-disulfonic acid but not lactate or alanine. Hepatic uptake of taurocholate in albumin solutions (2.5%) was twice as great as expected from estimates of the free taurocholate concentration. In contrast, equimolar concentrations of ovalbumin or bovine gamma-globulin had no effect on measured rates of taurocholate uptake and no evidence for a specific albumin receptor could be found on these hepatocytes by 125I-albumin binding. These studies indicate that a carrier-mediated, sodium-independent transport system for taurocholate uptake is present in skate hepatocytes that is not driven solely by the free concentration of taurocholate.

Na-H exchange regulates intracellular pH in isolated rat hepatocyte couplets.

Intracellular pH (pHi) was measured directly in isolated rat hepatocyte couplets using pH sensitive microelectrodes. The hepatocytes were maintained in a minimal salt buffer without added hormones or serum. Values of pHi (6.99 +/- 0.12, mean +/- SE) were close to their Nernst equilibria. After intracellular acidification with ammonium chloride, pH regulation was inhibited with 1 mM amiloride or by omission of external sodium, consistent with a Na-H exchange mechanism. Mean intracellular buffering power, in the nominal absence of carbon dioxide, was 34.1 +/- 11.4 mM. In the presence of external bicarbonate, amiloride or omission of sodium slowed, but did not completely inhibit recovery from acidification, indicating that additional pHi regulation mechanisms may operate in this preparation. These studies provide a direct measurement of pHi in hepatocyte couplets and indicate that Na-H exchange, together with a bicarbonate dependent system are important mechanisms for pHi regulation in this preparation.

Inhibition of water-sodium intestinal absorption by an atrial extract.

The rat atrium contains a diuretic and natriuretic factor which appears to inhibit the sodium reabsorption in the kidney tubules. We observed, in rats, that our atrial extract possesses a potent diuretic and natriuretic effect that was accompanied by an increased dextrose excretion. Similarly, extracts of rat atria, but not of ventricles, reduced intestinal absorption of water, sodium, and dextrose. The omission of sodium or dextrose in the perfusion fluid annulled this effect. These data suggest that the substance inhibiting the intestinal absorption of water and solutes is probably atrial natriuretic factor and that it acts on the sodium-dextrose cotransport mechanism.

Catecholamines in the coelenterate Renilla k�llikeri

The characteristics of uptake of 3H-noradrenaline (3H-NA) and 3H-adrenaline (3H-A) in the tissues of the sea pansy, Renilla kollikeri, were studied by in vivo incubations. Lineweaver-Burk plots indicated two components of catecholamine accumulation, one representing a high-affinity uptake with an apparent Km of 4.91×10-7 M (3H-NA) or 4.39×10-7 M (3H-A), and the other a low affinity process with an apparent Km of 5.52×10-5 M (3H-NA) or 1.49×10-5 M (3H-A). The high-affinity uptake of both tracers was strongly inhibited at low temperature and in a calcium-free medium, thus suggesting the involvement of a carrier-mediated transport mechanism, but was largely insensitive to sodium omission and ouabain. Accumulations of 3H-NA, but not 3H-A, were highly desipramine-sensitive.

The transport of (+)-amphetamine by the neuronal noradrenaline carrier.

PC-12 cells (a clonal line of rat phaeochromocytoma cells) take up noradrenaline by a transport system which is identical with the neuronal amine transport system ("uptake1"). The uptake of 3H-noradrenaline into reserpine-pretreated PC-12 cells (monoamine oxidase inhibited) was saturable (Km = 0.6 +/- 0.1 mumol/l), dependent on sodium and chloride, and competitively inhibited by (+)-amphetamine (Ki = 0.18 +/- 0.04 mumol/l), cocaine (Ki = 0.55 +/- 0.15 mumol/l) and desipramine (Ki = 4.3 +/- 0.6 nmol/l). The uptake and accumulation of 3H (+)-amphetamine showed characteristics comparable to those of 3H-noradrenaline, since the uptake of 3H (+)-amphetamine (0.1 mumol/l) was reduced by omission of sodium or chloride from the incubation medium. The sodium-sensitive component of uptake and accumulation of 3H (+)-amphetamine was fully inhibited by cocaine and desipramine. The IC50 of desipramine for inhibition of the sodium-sensitive component of the 1-min uptake of 3H (+)-amphetamine (20 nmol/l) was about 2 nmol/l, i.e., identical with the Ki for inhibition of uptake of 3H-noradrenaline. At concentrations above 1 mumol/l, desipramine additionally caused an inhibition of the sodium-independent permeation of 3H (+)-amphetamine into PC-12 cells. Hence, by using a homogeneous population of cells endowed with "uptake1", it is possible to demonstrate - besides a pronounced lipophilic entry - a carrier-mediated uptake of 3H (+)-amphetamine.