Mixed micelles of the anionic surfactant sodium dodecyl sulfate and the nonionic pentaethylene glycol mono-n-dodecyl ether in solution

Dynamic light scattering, surface tension, and clouding temperature have been monitored to elucidate the solution properties of mixed micelles formed between the anionic surfactant sodium dodecyl sulfate (SDS) and the nonionic surfactant pentaethylene glycol mono-n-dodecyl ether (C12E5) over a wide range of surfactant concentration and temperature. Addition of 0.1 M NaCl shifts the relaxational modes to higher frequency and lowers the clouding temperature (T-c) of the nonionic surfactant solution by about 1 degrees C compared to the salt-free system. T-c for the mixed surfactant solutions is higher than that of the binary C12E5 solutions and depends sensitively on the concentration of the two surfactants but increases only slightly when the total surfactant concentration is increased at a given molar C12E5/SDS concentration ratio. With C12E5/SDS = 5.7, for example, T-c is 46.0 and 47.5 degrees C, respectively, at 5 and 70 mM of C12E5 the mixed solutions are homogeneous and stable and contain nonspherical micelles, which are close to monodisperse over a range of surfactant concentrations and temperature. The mixed system has a lower Krafft point than binary SDS solutions and shows an approximately ideal behavior in contrast to the binary C12E5 solution. The hydrodynamic radius (RH) of the mixed micelle increases with temperature as do C12E5 micelles in the binary solutions and also with increasing C12E5/SDS ratio. At 25 degrees C, the critical micelle concentration of the mixed solution lies between those of the individual surfactants and decreases as the C12E5/SDS ratio is increased.

A new class of neurotoxin from wasp venom slows inactivation of sodium current

The effects of alpha-pompilidotoxin (alpha-PMTX), a new neurotoxin isolated from the venom of a solitary wasp, were studied on the neuromuscular synapses in lobster walking leg and the rat trigeminal ganglion (TG) neurons. Paired intracellular recordings from the presynaptic axon terminals and the innervating lobster leg muscles revealed that alpha-PMTX induced long bursts of action potentials in the presynaptic axon, which resulted in facilitated excitatory and inhibitory synaptic transmission. The action or alpha-PMTX was distinct from that of other known facilitatory presynaptic toxins, including sea anemone toxins and alpha-scorpion toxins, which modify the fast inactivation of Na+ current. We further characterized the action of alpha-PMTX on Na+ channels by whole-cell recordings from rat trigeminal neurons. We found that alpha-PMTX stowed the Na+ channels inactivation process without changing the peak current-voltage relationship or the activation time course of tetrodotoxin (TTX)-sensitive Na+ currents, and that alpha-PMTX had voltage-dependent effects on the rate of recovery from Na+ current inactivation and deactivating tail currents. The results suggest that alpha-PMTX slows or blocks conformational changes required for fast inactivation of the Na+ channels on the extracellular surface. The simple structure of alpha-PMTX, consisting of 13 amino acids, would be advantageous for understanding the functional architecture of Na+ channel protein.

EFFECT OF LATERAL HYPOTHALAMUS LESIONS ON THE WATER AND SALT INTAKE, AND SODIUM AND URINE EXCRETION INDUCED BY ACTIVATION OF THE MEDIAN PREOPTIC NUCLEUS IN CONSCIOUS RATS

In this-study we investigated the influence of electrolytic lesion of the lateral hypothalamus (LH) on the water and salt appetite, and the natriuretic, diuretic and cardiovascular effects induced by angiotensinergic, cholinergic and noradrenergic stimulation of the median preoptic nucleus (MnPO) in rats. Male Holtzman rats were implanted with a cannula into the MnPO. Other groups of sham- and LH-lesioned rats received a stainless steel cannula implanted into the MnPO. ANGII injection into the MnPO induced water and sodium intake, and natriuretic, diuretic, presser and tachycardic responses. Carbachol induced water intake, and natriuretic, presser and bradycardic responses, whereas noradrenaline increased urine, sodium excretion and blood pressure, and induced bradycardia. In rats submitted to LH-lesion only, water and sodium intake was reduced compared with sham rats. LH lesion also reduced the sodium ingestion induced by ANGII (12 ng) into the MnPO. In LH-lesioned rats, the dipsogenic, diuretic and presser responses induced by ANGII (12 ng), carbachol (2 nmol) and noradrenaline (20 nmol) injection into the MnPO were reduced. The same occurred with sodium excretion when carbachol (2 nmol) and noradrenaline (20 nmol) were injected into the MnPO of LH-lesioned rats, whereas ANGII(12 ng) induced an increase in sodium excretion. These data show that electrolytic lesion of the LH reduces fluid and sodium intake, and presser responses to angiotensinergic, cholinergic and noradrenergic activation of the MnPO. LH involvement with MnPO excitatory and inhibitory mechanisms related to water and sodium intake, sodium excretion and cardiovascular control is suggested.

Central interaction between atrial natriuretic peptide and angiotensin II in the control of sodium intake and excretion in female rats

We investigated the effects of estrogen on sodium intake and excretion induced by angiotensin II (ANG II), atrial natriuretic peptide (ANP) or ANG II plus ANP injected into the median preoptic nucleus (MnPO). Female Holtzman rats weighing 250-300 g were used. Sodium ingestion and excretion 120 min after the injection of 0.5 mu l of 0.15 M NaCl into the MnPO were 0.3 +/- 0.1 ml (N = 12) and 29 +/- 7 mu Eq in intact rats, 0.5 +/- 0.2 ml (N = 10) and 27 +/- 6 mu Eq in ovariectomized rats, and 0.2 +/- 0.08 (N = 11) and 38 +/- 8 mu Eq in estrogen-treated ovariectomized (50 mu g/day for 21 days) rats, respectively. ANG II (21 mu M) injection in intact, ovariectomized, and estrogen-treated ovariectomized rats increased sodium intake (3.8 +/- 0.4, 1.8 +/- 0.3 and 1.2 +/- 0.2 ml/120 min, respectively) (N = 11) and increased sodium excretion (166 +/- 18, 82 +/- 22 and 86 +/- 12 mu Eq/120 min, respectively) (N = 11). ANP (65 mu M) injection in intact (N = 11), ovariectomized(N = 10)and estrogen-treated ovariectomized (N = 10) rats increased sodium intake (1.4 +/- 0.2, 1.8 +/- 0.3, and 1.7 +/- 0.3 ml/120 min, respectively) and sodium excretion (178 +/- 19, 187 +/- 9, and 232 +/- 29 mu Eq/120 min, respectively). Concomitant injection of ANG II and ANP into the MnPO of intact (N = 12), ovariectomized (N = 10) and estrogentreated ovariectomized (N = 10) rats caused smaller effects than those produced by each peptide given alone: 1.3 +/- 0.2, 0.9 +/- 0.2 and 0.3 +/- 0.1 ml/120 min for sodium intake, respectively, and 86 +/- 9, 58 +/- 7, and 22 +/- 4 mu Eq/120 min for sodium excretion, respectively. Taken together, these results demonstrate that there is an antagonistic interaction of ANP and ANG II on sodium intake and excretion, and that reproductive hormones affect this interaction.

pH at the micellar interface: Synthesis of pH probes derived from salicylic acid, acid-base dissociation in sodium dodecyl sulfate micelles, and Poisson-Boltzmann simulation

The study of the H+ concentration at the micellar interface is a convenient system for modeling the distribution of H+ at interfaces. We have synthesized salicylic acid derivatives to analyze the proton dissociation of both the carboxylic and phenol groups of' the probes, determining spectrophotometrically the apparent pK(a)'s (pK(ap)) in sodium dodecyl Sulfate, SDS, micelles with and without added salt. The synthesized probes were 2-hydroxy-5-(2-trimethylammoniumacetyl)benzoate; 2-hydroxy-5-(2-dimethylhexadecylammoniumacetyl)benzoate- 2-hydroxy-5-(2-dimethylhexadecylammoniumhexanoyl)benzoate-, 2-hydroxy-5-(2-diniethylhexadecylammoniumundecanoyl)betizoate; 2-hydroxy-5-acetylbenzoic acids and 2-hydroxy-5-dodecanoylbenzoic acid. Upon incorporation into SDS micelles the pK(ap)'s of both carboxylic and phenol groups increased by ca. 3 pH units and NaCl addition caused a decrease in the probe-incorporated pKap. The experimental results were fitted with a cell model Poisson-Boltzmann (P-B) equation taking in consideration the effect of salt on the aggregation number of SDS and using the distance of' the dissociating group as a parameter. The conformations of the probes were analyzed theoretically using two dielectric constants, e.g., 2 and 78. Both the P-B analysis and conformation calculations can be interpreted by assuming that the acid groups dissociate very close to, or at, the interface. Our results are consistent with the assumption that the intrinsic pK(a)'s of both carboxylic and phenol groups of the salicylic acid probes used here can be taken as those in water. Using this assumption the micellar and salt effects on the pKap's of the (trialkylammonium)benzoate probes were described accurately using a cell model P-B analysis. (c) 2005 Elsevier B.V. All rights reserved.

Influence of ionic interactions on the photoinduced Birefringence of poly[1-[4-(3-carboxy-4 hydroxyphenylazo) benzene sulfonamido]-1 2-ethanediyl, sodium salt] films

Electrostatic interactions govern most properties of polyelectrolyte films, as in the photoinduced bire-fringence of azo-containing polymers. In this paper we report a systematic investigation of optical storage characteristics of cast and layer-by-layer (LbL) films of poly[1 -[4-(3-carboxy-4 hydroxypheny-lazo) benzene sulfonamido]-1,2-ethanediyl, sodium salt] (PAZO). Birefringence was photoinduced faster in PAZO cast films prepared at high pHs, with the characteristic writing times decreasing almost linearly with the pH in the range between 4 and 9. This was attributed to an increased free volume for the azochromophores with the enhanced electrostatic repulsion in PAZO charged to a greater extent. In contrast, in LbL films of PAZO alternated with poly(allylamine hydrochloride) (PAH), the electrostatic interactions between the oppositely charged polymers hampered photoisomerization and molecular rearrangement, thus leading to a slower writing kinetics for highly charged PAH or PAZO.

Voltammetric sensor for sodium nitroprusside determination in biological fluids using films of poly-L-lysine

Sodium nitroprusside (NP), a commercial vasodilator, can be pre-concentrated on vitreous carbon electrode modified by films of 97.5%: 2.5% Poly-L-lysine (PLL): glutaraldehyde (GA). This coating gives acceptable anion exchange properties whilst giving the required improvement of adhesion to the glassy carbon electrode surface. Linear response range and detection limit on nitroprusside in B-R buffer pH 4.0, were 1 x 10(-6) to 2 x 10-(5) mol L-1 and 1 x 10(-7) mol L-1, respectively. The repeatability of the proposed sensor, evaluated in term of relative standard deviation, was measured as 4.1% for 10 experiments. The voltammetric sensor was directly applied to determination of nitroprusside in human plasma and urine samples and the average recovery for these samples was around 95-97% without any pre treatment.

Effects of different treatments on purity of silica from soluble sodium silicate

Noncrystalline silica was obtained with low iron, sodium, and nitrate ions concentrations from soluble sodium silicate (water glass) and nitric acid solution. Extractions with nitric acid solution and/or deionized water and/or dialysis were carried out to eliminate soluble metal ions. Products were dried in a microwave oven and characterized by chemical analysis, XRD, and IR. Dialysis seems to be the best treatment for the elimination of sodium and nitrate ions. Silica purified by nitric acid and water extractions followed by dialysis yields the purest silica sample.

Novel wasp toxin discriminates between neuronal and cardiac sodium channels

Pompilidotoxins (PMTXs), derived from the venom of solitary wasp has been known to facilitate synaptic transmission in the lobster neuromuscular junction, and a recent further study from rat trigeminal neurons revealed that the toxin slows Na+ channel inactivation without modifying activation process. Here we report that beta -PMTX modifies rat brain type II Na+ channel alpha -subunit (rBII) expressed in human embryonic kidney cells but fails to act on the rat heart alpha -subunit (rH1) at similar concentrations. We constructed a series of chimeric mutants of rBII and rH1 Na+ channels and compared modification of the steady-state Na+ currents by beta -PMTX. We found that a difference in a single amino acid between Glu-1616 in rBII and Gln-1615 in rH1 at the extracellular loop of D4S3-S4 is crucial for the action of beta -PMTX. PMTXs, which are small peptides with 13 amino acids, would be a potential tool for exploring a new functional moiety of Na+ channels.

Effect of ion reduction of sodium, calcium and potassium on spontaneous contraction of the esophagus of Pomacea lineata SPIX, 1827 (Mollusca-Gastropoda-Prosobranchia)

The invertebrate's musculature still presents many elusive points, especially in molluscs that generally present smooth and cracked fibers with peculiar characteristics. It was found that the molluscs reactions to the ion variation in the bathing are not very clear, mainly in view of the isolated reduction or equivalent of the ions. Suspended in bath, the isolated esophagus of the P. lineata exhibited spontaneous activity. This rhythmic activity was sensitive to the ion variation of the perfusion liquid, evidenced by alterations in the spontaneous contractions. The equivalent reduction of the ion reduced the spontaneous activity, evidenced by the amplitude reduction of the response, besides maintaning an organ contraction, primarily in the reductions below 50%. When the isolated reductions of the Na, Ca or K ion were performed, occurred interference in the spontaneous contractions of the organs, principally in amplitude of the response and maintenance of the contracture in reductions of 50 and 25% of the ion.

Bombesin affects the central nervous system to produce sodium intake inhibition in rats

Bombesin (BN) elicits in the rat important behavioural modifications, including inhibition of food and of water intake. Recently, it has been observed that the peptide also inhibits the intake of sodium chloride. To stare whether BN possesses a selective antinatriorexic effect or it elicits only an aspecific depression of ingestive behaviour, we studied the effects of this peptide on the intake of sodium, water or sucrose of Wistar rats after injections into the fourth brain ventricle or into selected brain areas involved in the control of sodium intake, containing BN-like peptides and/or their precursors or specific receptors. We observed that: a) BN (100-200 ng/rat) injected into the fourth brain ventricle inhibits not only the intake of 2% NaCl of sodium depleted rats but also that of water and of 5% sucrose; b) BN (5-50 ng/rat) administered into the nucleus of the solitary tract and the medial amygdala does not influence the intake of these fluids and c) BN (5-50 ng/rat) injected into the paraventricular nucleus does not influence the intake of water and 5% sucrose but potently inhibits that of 2% NaCl. We concluded that the inhibitory effect elicited on salt intake by intracranial administration of BN is selective for this behaviour and is not the expression of an aspecific depression of ingestive behaviour. (C) 1998 Elsevier B.V.