Replacement Of Sodium Ions Research Articles

Sodium spirulan as a potent inhibitor of arterial smooth muscle cell proliferation in vitro

Sodium spirulan (Na-SP) is a sulfated polysaccharide with M r ∼220,000 isolated from the blue-green alga Spirulina platensis. The polysaccharide consists of two types of disaccharide repeating units, O-hexuronosyl-rhamnose (aldobiuronic acid) and O-rhamnosyl-3- O-methylrhamnose (acofriose) with sulfate groups, other minor saccharides and sodium ion. Since vascular smooth muscle cell proliferation is a crucial event in the progression of atherosclerosis, we investigated the effect of Na-SP on the proliferation of bovine arterial smooth muscle cells in culture. It was found that Na-SP markedly inhibits the proliferation without nonspecific cell damage. Either replacement of sodium ion with calcium ion or depolymerization of the Na-SP molecule to M r ∼14,700 maintained the inhibitory activity, however, removal of sodium ion or desulfation markedly reduced the activity. Heparin and heparan sulfate also inhibited vascular smooth muscle cell growth but their effect was weaker than that of Na-SP; dextran sulfate, chondroitin sulfate, dermatan sulfate and hyaluronan failed to inhibit the cell growth. The present data suggest that Na-SP is a potent inhibitor of arterial smooth muscle cell proliferation, and the inhibitory effect requires a certain minimum sequence of polysaccharide structure whose molecular conformation is maintained by sodium ion bound to sulfate group.

Magnetism in organic ion radical salts and complexes based on nitronyl nitroxide

In order to study effects of magnetic and non-magnetic counter ions on the magnetism in organic radical crystals, alkali metal and transition metal salts of carboxylatofuryl nitronyl nitroxide were synthesized. Guanidinium sulfonatofuryl nitronyl nitroxide complex was also prepared and compared its magnetism with that of the sodium salt. Magnetization measurements reveal that ferromagnetic intermolecular interaction, which is coexistent with antiferromagnetic one, in 2-carboxyfuryl nitronyl nitroxide is disappeared by inserting alkali-metal ions. Insertion of manganese, cobalt and copper ions into 2-carboxyfuryl nitronyl nitroxide results in complex behavior, suggesting in part ferromagnetic interaction, in temperature dependence of magnetic susceptibility. Replacement of sodium ion with larger guanidinium ion in 2-sulfonatofuryl nitronyl nitroxide yields weaker interlayer antiferromagnetic interaction.

Ion-Exchange Chromatography/Electrospray Mass Spectrometry for the Identification of Organic and Inorganic Species in Topiramate Tablets

An ion-exchange chromatograph/electrospray ionization mass spectrometer (IC/ESI-MS) was used successfully to identify organic and inorganic species present in topiramate tablets. An ion suppressor is placed between the column and detectors to replace sodium ions in the mobile phase with hydrogen ions supplied by the suppressor. The ensuing combination of the hydrogen ions with the mobile phase hydroxide ions produces water and thus allows simultaneous ion detection by an ion conductivity detector and a mass spectrometer. Analytes, including lactate, glycolate, chloride, formate, sulfate, and oxalate, were unambiguously identified by matching the mass spectra and retention times with those of the authentic compounds. Due to its capability of detecting positive and negative as well as neutral species, ESI-MS provides valuable information which is not available with ion conductivity detection alone. Though the coupling of ion-exchange chromatography to mass spectrometry has been reported previously, this is the first demonstration of IC/ESI-MS for the identification of unknown species in real samples. Finally, with the use of deuterium/carbon-13 labeling and MS/MS techniques, we have confirmed that oxalic acid (HOOC-COOH) is formed from formic acid (HCOOH) at the electrospray interface in the presence of the electric field. This observation not only confirms the identity of an unknown peak, but it also provides new insight into chemistry that can take place during electrospray ionization.

Transport of dehydroepiandrosterone and dehydroepiandrosterone sulphate into rat hepatocytes

The purpose of the present study was to characterize the transport of dehydroepiandrosterone (DHEA) and dehydroepiandrosterone sulphate (DHEAS) into hepatocytes at physiological and pharmacological concentrations. Hepatocytes were isolated from female Sprague-Dawley rats by collagenase perfusion. Uptake of [ 3H]DHEA and [ 3H]DHEAS at increasing concentrations (3.5 nM-100 μM) was measured by the rapid filtration technique at 30 s intervals up to 120 s. The uptake of DHEAS by hepatocytes was saturable ( K m = 17.0 μM; V max = 3.7 nmol/min/mg cell protein). In contrast, a specific saturable transport system for DHEA could not be detected in rat hepatocytes. It is suggested that DHEA enters the cell by diffusion. The uptake of DHEAS could be inhibited by antimycin A, carbonylcyanide- m-chlorophenylhydrazone, and dinitrophenol (inhibitors of the mitochondrial respiratory chain), by dinitrofluorobenzene and p-hydroxymercuribenzoate (NH 2- and SH-blockers, respectively), and by monensin (Na +-specific ionophore). No inhibition was seen in the presence of ouabain (inhibitor of Na +-K +-ATPase) and phalloidin (inhibitor of cholate transport and actin-blocker). Interestingly, DHEAS uptake was inhibited by bile acids (cholate, taurocholate and glycocholate). Conversely, [ 3H]cholate uptake was strongly inhibited by DHEAS, which indicates a competition for the same carrier. Replacement of sodium ion with choline markedly decreased uptake velocity at pharmacological DHEAS concentrations. The results suggest that DHEAS uptake is a saturable, energy-dependent, carrier-mediated, partially Na +-dependent process, and that DHEAS may be taken up via the multispecific bile acid transport system.

Alteration of Smectite in a System Including Alanine at High Pressure and Temperature

AbstractTransformation of montmorillonite was experimentally investigated using a model system of montmorillonite-alanine at 100 MPa and up to 500°C. Sodium-montmorillonite changed to a mixed layer mineral of sodium- and ammoniumn-montmorillonites (Na/NH4-Mnt) in the temperature range from 150 to 400°C. Ammonium ions were the decomposition product of alanine above 150°C. The Na/NH4-Mnt transformed to regularly and randomly interstratified minerals of NH4-montmorillonite and NH4-mica (o. NH4-Mnt/NH4-Mic and d. NH4-Mnt/NH4-Mic) at 400°C. These mixed layered minerals transformed to ammonium-mica at 500°C. Ammonium-analcime appeared and coexisted with the smectites at temperatures over 200°C, and with albite for those over 400°C.In comparison with the results of previous experiments in which there was no organic component, the present results revealed that (1) some uncommon mineral phases appeared by replacement of sodium ions in montmorillonite with ammonium ions, i.e., NH4-Mic, o. and d. NH4-Mnts, o. and d. NH4-Mnt/NH4-Mics, and (2) ammonium-analcime appeared. The mineral assemblages and alteration sequences correspond better with those observed in the natural system than those known from experimental results in aluminosilicate-water system.

Cellular accumulation of antineoplaston AS21 in human hepatoma cells.

Antineoplaston AS2-1 is a mixture of sodium salts of phenylacetic acid (PAA) and phenylacetylglutamine (PAG) in the ratio 4:1. The uptake of both compounds has been examined in human hepatoma cell line, Hep G-2. The accumulation of PAA was characterized by temperature sensitivity, saturability and energy dependency. Organic anions (probenecid, p-aminonohippuric acid and stilbene) inhibited PAA uptake suggesting the involvement of organic anion system in PAA transport. PAG cellular uptake exhibited dependency on metabolic energy, since the accumulation was sensitive to lowered temperature as well as to replacement of sodium ions by choline in the incubation medium. In contrast, the process showed tolerance to lithium ions as a substitute to sodium ions. This finding, together with the strong inhibition of PAG accumulation by histidine and glutamine, indicates that system N, known to be specific for hepatic tissue and the glutamine-preferring amino acid transport system, mediates PAG uptake. We conclude that PAG, through competition with glutamine for the same membrane carrier, may reduce glutamine transport leading to intracellular glutamine depletion. The physiological consequence of this biochemical event could be critical to cancer cells and therefore might contribute to the mechanism of antineoplaston AS2-1 action.

Sodium-dependent receptor current in a new mechanoreceptor preparation

1. Intracellular microelectrodes recorded the receptor potential and receptor current in the neurons of spider slit sense organs during mechanical stimulation of the slits. 2. Mechanical stimulation produced two patterns of action potential discharge, corresponding to the two groups of neurons described previously by electrical stimulation. 3. Tetrodotoxin eliminated the action potentials and revealed a receptor potential with both static and adapting components. Voltage clamp gave an inward receptor current with a similar time course. 4. Replacement of sodium ions in the bath reversibly eliminated the receptor current, indicating that it is carried by sodium ions. However, this effect was comparatively slow, suggesting that the tips of the sensory dendrites lie in a chemically restricted environment.

Bradykinin excites tetrodotoxin-resistant primary afferent fibers

Bradykinin is a nonapeptide that plays a central role in the production of pain and inflammation. A horizontal spinal cord slice preparation with attached dorsal root and dorsal root ganglion was used to study the effect of bradykinin on afferent fibers. Intracellular recordings were made from dorsal root ganglion and dorsal horn neurons. Bath application of bradykinin (1 μM) to the dorsal root ganglion compartment produced a depolarization ( 5 ± 0.8mV) and firing of action potentials in eight out of eighteen dorsal root ganglion neurons tested. Simultaneous intracellular recordings from dorsal horn neurons revealed that the application of bradykinin to dorsal root ganglion, peripheral nerve trunk or dorsal root resulted in the synaptic activation of dorsal horn neurons. The depolarizing effect of bradykinin on the dorsal root ganglion neurons and its synaptic excitatory effect on dorsal horn neurons was abolished by pretreatment of the same segment of sensory neurons by a B2 bradykinin receptor antagonist ( d-Arg 0, Hyp 3,β-Thi 5,8, dPhe 7)-bradykinin (5 μM). Bath application of tetrodotoxin (TTX; 0.2–1 μM) to the sensory neurons blocked electrically-evoked action potentials in large dorsal root ganglion neurons and, consequently, excitatory postsynaptic potentials in dorsal horn neurons evoked by electrical activation of low threshold afferent fibers. However, the stimulatory effects, both depolarization and firing of action potentials, of bradykinin were resistant to TTX. Replacement of sodium ions with TRIS completely abolished the stimulatory effect of bradykinin on the sensory neurons. Bradykinin potentiated the postsynaptic potentials induced by electrical stimulation of TTX-resistant afferent fibers. The facilitation of transmission was measured as an increase of 232 ± 32% ( n = 7) in the size (area under the curve) of the TTX-resistant slow excitatory postsynaptic potential and about 180% increase in the number of action potentials fired. Our data suggest the presence of a population of primary afferent fibers that become responsive to electrical stimulation in the presence of bradykinin and these could be responsible for hyperalgesia.

Improved electrospray ionization of synthetic oligodeoxynucleotides

AbstractA method is described for rapid purification of synthetic oligodeoxynucleotides to remove sodium counter ions prior to electrospray ionization mass spectrometry. The oligomers, following purification by gel electrophoresis, are precipitated from ammonium acetate to replace sodium ions by ammonium ions, and dissolved in water. Negative‐ion electrospray spectra are presented for oligomers with up to 48 residues in which the most intense peaks correspond to the [MnH]n− ion. The spectrum of 77‐mer (Mr24039) shows the predominant peak as due to retention of only a single sodium ion. Changes in the spectra are reported for different instrument orifice voltages and different solution pH. The method should permit rapid, accurate analysis of most typical, synthetic oligodeoxynucleotides.

Sodium ion-dependent amino acid transport in membrane vesicles of Bacillus stearothermophilus.

Amino acid transport in membrane vesicles of Bacillus stearothermophilus was studied. A relatively high concentration of sodium ions is needed for uptake of L-alanine (Kt = 1.0 mM) and L-leucine (Kt = 0.4 mM). In contrast, the Na(+)-H(+)-L-glutamate transport system has a high affinity for sodium ions (Kt less than 5.5 microM). Lithium ions, but no other cations tested, can replace sodium ions in neutral amino acid transport. The stimulatory effect of monensin on the steady-state accumulation level of these amino acids and the absence of transport in the presence of nonactin indicate that these amino acids are translocated by a Na+ symport mechanism. This is confirmed by the observation that an artificial delta psi and delta mu Na+/F but not a delta pH can act as a driving force for uptake. The transport system for L-alanine is rather specific. L-Serine, but not L-glycine or other amino acids tested, was found to be a competitive inhibitor of L-alanine uptake. On the other hand, the transport carrier for L-leucine also translocates the amino acids L-isoleucine and L-valine. The initial rates of L-glutamate and L-alanine uptake are strongly dependent on the medium pH. The uptake rates of both amino acids are highest at low external pH (5.5 to 6.0) and decline with increasing pH. The pH allosterically affects the L-glutamate and L-alanine transport systems. The maximal rate of L-glutamate uptake (Vmax) is independent of the external pH between pH 5.5 and 8.5, whereas the affinity constant (Kt) increases with increasing pH. A specific transport system for the basic amino acids L-lysine and L-arginine in the membrane vesicles has also been observed. Transport of these amino acids occurs most likely by a uniport mechanism.

Characterization of amino acid transport in membrane vesicles from the thermophilic fermentative bacterium Clostridium fervidus

Amino acid transport was studied in membrane vesicles of the thermophilic anaerobic bacterium Clostridium fervidus. Neutral, acidic, and basic as well as aromatic amino acids were transported at 40 degrees C upon the imposition of an artificial membrane potential (delta psi) and a chemical gradient of sodium ions (delta microNa+). The presence of sodium ions was essential for the uptake of amino acids, and imposition of a chemical gradient of sodium ions alone was sufficient to drive amino acid uptake, indicating that amino acids are symported with sodium ions instead of with protons. Lithium ions, but no other cations tested, could replace sodium ions in serine transport. The transient character of artificial membrane potentials, especially at higher temperatures, severely limits their applicability for more detailed studies of a specific transport system. To obtain a constant proton motive force, the thermostable and thermoactive primary proton pump cytochrome c oxidase from Bacillus stearothermophilus was incorporated into membrane vesicles of C. fervidus. Serine transport could be driven by a membrane potential generated by the proton pump. Interconversion of the pH gradient into a sodium gradient by the ionophore monensin stimulated serine uptake. The serine carrier had a high affinity for serine (Kt = 10 microM) and a low affinity for sodium ions (apparent Kt = 2.5 mM). The mechanistic Na+-serine stoichiometry was determined to be 1:1 from the steady-state levels of the proton motive force, sodium gradient, and serine uptake. A 1:1 stoichiometry was also found for Na+-glutamate transport, and uptake of glutamate appeared to be an electroneutral process.

Replacement of sodium ions by cryptate (C222) complexed barium ions in sodium dodecyl sulfate micelles studied by electron spin resonance and electron spin-echo modulation of 5-doxylstearic acid and N,N,N',N'-tetramethylbenzidine photoionization and by viscosity measurements

Ultraviolet irradiation of solubilized N,N,N{prime},N{prime}-tetramethylbenzidine (TMB) and viscosity measurements have been carried out at room temperature in mixed micellar solutions of sodium dodecyl sulfate (SDS) and barium dodecyl sulfate (Ba(DS){sub 2}). The barium ions were complexed by the macrocyclic cryptate C222. The irradiations did not lead to constant photoionization yields in the barium/C222-containing solutions because of secondary reactions. The viscosity as a function of the Ba{sup 2+}/2 mole fraction (X) changed from 1.47 mPa s at X = 0 to 1.33 mPa s at X = 1, passing through a maximum at X = 0.2. At 77 K in frozen solutions the TMB photoionization yield as measured by electron spin resonance increased by a factor of 1.8 in the range X = 0-0.2 and leveled off at larger X. Deuterium modulation depths of electron spin-echo decay curves measured at 4.2 K for TMB{sup +} and 5-doxylstearic acid increase as a function of X in a similar way as the photoionization yields. The results indicate a higher local concentration of water molecules in the micellar surface region when the C222-complexed barium ions are present.

Osmotic regulation of prolactin secretion. Possible role of chloride.

The role of osmotic pressure in the exocytosis of prolactin from rat pituitary tumor (GH) cells in culture was investigated. Reducing the osmotic strength of the medium from 300 mosm to 150 mosm by removal of NaCl did not alter basal secretion of prolactin but inhibited secretion stimulated by thyrotropin-releasing hormone (TRH) and forskolin. Both basal and stimulated secretion of prolactin were inhibited by increasing the osmotic strength of the medium with NaCl (IC50 at approximately 500 mosm). The stimulated release of hormone from GH-cells was independent of sodium and unaffected by replacement of sodium ion with tetramethylammonium or choline, or by addition of 500 nM tetrodotoxin. Secretagogue-stimulated release was, however, dependent upon chloride. Exchange of medium chloride with benzoate or isethionate significantly inhibited the stimulated release of prolactin (IC50 at approximately 60 mM exchange) regardless of the secretagogue utilized (phorbol ester, forskolin, depolarization plus BAY K8644, or TRH). Exchange of medium chloride with either isethionate or benzoate reduced cell volume by 10% compared to 60% for sucrose and mannitol, suggesting that inhibition of secretion by isethionate exchange was not a result of increased intracellular osmotic pressure. Complete exchange of medium chloride with isethionate did not alter equilibrium [3H]methyl-TRH binding, resting internal [Ca2+], or the [Ca2+]i response to depolarization and TRH as measured with intracellularly trapped Fura 2. Chloride removal did not change resting internal pH and recovery from an acid load as measured by the intracellular pH-sensitive dye 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein. The stimulated secretion of prolactin was also inhibited by exchange of chloride with isethionate in normal pituitary cells in primary culture and the ability of normal cells to respond to the dopamine agonist bromocryptine was not affected by the exchange. These results suggest that exocytosis of prolactin from GH-cells and normal pituitary cells in culture is an osmotically driven process that is chloride-dependent. Stimulated release is more chloride-dependent than constitutive release. The inhibitory effect of isethionate substitution occurs after signal transduction and is distinct from the site of dopamine inhibition of prolactin release.

The absorption of free and “Peptide” amino acids in the small intestine of chicks

1. 1. The accumulation of free l-tryptophan and glycine in the small intestine of chicks, as well as of amino acids released at the hydrolysis of glycyl- l-tryptophan, glycyl- l-leucine and glycyl- l-valine, was studied under experiments in vitro with accumulating preparations of chicks intestinal mucosa. 2. 2. At the incubation of accumulating mucosal preparations (AMP) in a medium containing the investigated compounds in the presence of sodium ions (140 mM) or an equal amount of potassium ions, the existence of 2 ways of their transport was found: sodium-independent and sodium-dependent. The latter is decisive for the transport of free l-tryptophan. 3. 3. In the case of peptide l-tryptophan the power of both mechanisms is about the same, but in case of free glycine the sodium-independent mechanism is dominant. 4. 4. The transport of peptide glycine is realized only through the sodium-independent mechanism. 5. 5. The existence of amino acid transport against the gradient is noted by replacing sodium by potassium ions in the incubation medium. Its absence was observed at the incubation of AMP under anaerobic conditions. 6. 6. The study of kinetics of l-tryptophan accumulation showed that the replacement of sodium ions by potassium ones in the incubation medium is accompanied by a decrease of K t from 2.23 to 0.84 mM as well as of V from 4.54 to 0.84 mM/min per cm. 7. 7. Modifiers ( l-valine, l-threonine, l-α-alanine) in concentrations of 100 mM inhibit drastically the accumulation of free and peptide l-tryptophan in the mucosa of chick small intestine, and this effect is mainly related to the action of sodium-dependent transport mechanisms.

Interactions of guanidinium ions with sodium channels in frog myelinated nerve fibre.

1. The effects of external guanidinium ions on fast and slow inactivating currents flowing through sodium channels of the frog myelinated nerve fibre (Benoit, Corbier & Dubois, 1985) were analysed under voltage-clamp conditions. 2. When external sodium ions were partially replaced by guanidinium ions, the fast inactivating current was preferentially reduced and was absent in a solution containing guanidinium ions as the only external permeant cations. The inactivation time constants of both fast and slow currents were not significantly modified by the replacement of sodium ions by guanidinium ions. 3. Substitution of guanidinium ions for all sodium ions shifted the steady-state inactivation curve of the slow inactivating current towards positive voltages. 4. The voltage dependence of the activation of fast and slow inactivating currents was shifted towards positive voltages by guanidinium ions. Moreover, the activation-voltage curve of the slow inactivating current, which was biphasic under control conditions, was monophasic when guanidinium ions were substituted for all sodium ions. 5. Whereas the slow inactivating current could be carried by guanidinium ions, these cations were not only impermeant through the sodium channels which give rise to the fast inactivating current but also blocked this type of channel with an apparent dissociation constant of 49 mM. 6. It is concluded that guanidinium appears to be an efficient tool for further separating the two types of inactivating current and studying the properties of the slow inactivating current. These results are consistent with the suggestion that there are two types of sodium channels, fast and slow, with guanidinium ions being permeant only through the slow ones.

Carnitine transport in human intestinal biopsy specimens: Demonstration of an active transport system

Although carnitine is present in a variety of foods, the mechanism of its absorption has not been previously studied in humans. We investigated the absorption of carnitine by studying uptake into human intestinal mucosal biopsy specimens. We found evidence of active transport in the duodenum and ileum, but not in the colon. We demonstrated that intracellular concentrations exceeded concentrations in the incubation media at steady states and that uptake against a concentration gradient was abolished by anoxia and by replacement of sodium ion with potassium. Studies of initial rate of uptake over a range of concentrations revealed a curve consistent with a two-component system: a saturable system with a kt of 558 μM and a linear component probably representing passive diffusion. Addition of d-carnitine and l-acetylcarnitine resulted in diminished uptake of l-carnitine, suggesting that these substrates utilize the same transport mechanism. These studies demonstrate the presence of an active intestinal transport system for l-carnitine in human intestinal mucosa.

Studies on the interaction of cholesterol with soluble and insoluble elastins

The exchange of 3H-cholesterol in an aqueous solution of taurodeoxycholate with insoluble elastin and kappa-elastin peptides has been quantitatively studied. At higher cholesterol concentrations, and in similar experimental conditions, 0.3 μg and 0.2 μg of cholesterol could be adsorbed, respectively, on to 1 mg insoluble elastin and 1 mg kappa-elastin coacervate. Therefore, the above amounts of cholesterol fixed per mg elastin represent minimal estimates. The replacement of Na + ions by Ca 2+ ions increased the cholesterol binding both of fibrous and of soluble elastins. The binding curves tend towards a limiting value in the presence of Na +, but no saturation effect was observed in the presence of Ca 2+. The replacement of sodium ions by calcium ions in the taurodeoxycholate solutions also lowered the coacervation temperature of the kappa-elastin peptides. Fibrous elastin retained more cholesterol at 65°C than at 37°C, suggesting the importance of hydrophobic interactions in cholesterol elastin association. These results suggest that conformational changes could be induced in both soluble and insoluble forms of elastin by calcium ions increasing their affinity for cholesterol. This enhancement of cholesterol fixation by elastin in the presence of Ca 2+ ions may well have a physiopathological importance. So does also the fact that elastin-peptides exhibit a higher affinity in the presence of Ca 2+ for cholesterol than insoluble elastin, suggesting the possibility of increased cholsterol (and calcium) fixation as elastin is degraded in situ by elastases.

Carnitine transport in rat small intestine

Although L-carnitine has been given orally to patients with systemic carnitine deficiency with successful control of the disease and is present in a variety of dietary sources, there is little available information on the physiology of its absorption. We therefore studied intestinal carnitine absorption in the rat by measuring the uptake of radioactive L-carnitine by everted intestinal rings and sacs. Active transport was demonstrated in duodenum and jejunum, but not ileum, with intracellular concentrations higher than medium concentrations at steady state and by the prevention of concentration gradients with anoxia, metabolic inhibitors, and replacement of sodium ion. Studies of the relationship of uptake to carnitine concentration demonstrated the presence of two components of transport: a saturable component (with a Km of between 206 and 316 microM) that could be inhibited by the metabolically inactive D-isomer and by acetylcarnitine and a linear component that we presume represents diffusion.

Cation specificity of 3H-sulpiride binding involves alteration in the number of striatal binding sites

Specific 3H-sulpiride binding to rat striatal membranes shows an absolute requirement for the presence of sodium ions in the incubation buffer. Potassium, rubidium and caesium ions were unable to initiate specific 3H-sulpiride binding in a sodium free buffer, and lithium ionscould only partially replace sodium ions. Specific 3H-spiperone binding was unaffected by variation of the cation content of the incubation buffer. The alteration in 3H-sulpiride binding caused by sodium and lithium ions was due predominantly to an increase in the number of available binding sites, rather than to altered receptor affinity. Sodium ions may be essential for the accessability of 3H-sulpiride to a single site labelled also by 3H-spiperone. However, the Ki value for sulpiride displacement of 3H-spiperone in the presence of sodium ions was 20 times greater than the K D value for 3H-sulpiride binding. So, 3H-sulpiride may interact with a highly sodium dependent binding site distinct from that labelled by 3H-spiperone.

Ionic mechanisms of the fast (nicotinic) phase of the acetylcholine response of identified Planorbarius corneus neurons

Responses to electrophoretic application of acetylcholine and suberyldicholine were investigated in identified neurons (LPed-2 and LPed-3) isolated from the left pedal ganglion ofPlanorbarius corneus. When microelectrodes filled with potassium chloride were used the reversal potentials of responses to acetylcholine and suberyldicholine were less negative than when microelectrodes filled with potassium sulfate were used; these reversal potentials were shifted toward depolarization if chloride ions in the medium were replaced by sulfate. These facts indicate that the responses in both LPed-2 and LPed-3 depend on chloride ions. Reversal potentials for acetylcholine and suberyldicholine in LPed-3 were virtually identical (−51 and −50 mV respectively), but in LPed-2 they differed significantly (−46 and −62 mV respectively). Replacement of sodium ions by Tris ions shifted the reversal potential for acetylcholine in LPed-2 toward hyperpolarization but did not change the reversal potential for suberyldicholine. Benzohexonium had the same action. The reversal potential for acetylcholine in medium with a reduced sodium concentration or in the presence of benzohexonium was the same as for suberyldicholine. It is concluded that on neuron LPed-2 acetylcholine activates both acetylcholine receptors which control conductance for chloride ions and acetylcholine receptors which change conductance for sodium ions, whereas suberyldicholine acts only on acetylcholine receptors responsible for the chloride conductance of the membrane.