Search PubMed⌕ Search

Biomedical subjects

S A Simon

Publications and source records attributed to S A Simon.

At least 109 records · Page 6Linked to original sources
PubMed1988

Activation by odorants of a multistate cation channel from olfactory cilia.

Single-channel records were obtained after fusion of ciliary membranes from the olfactory epithelium of Rana catesbeiana to planar lipid bilayers, and odorant-activated cation-selective channels were identified. In addition, a 190-pS potassium-selective channel and a 40-pS cation-selective channel were found in a 0.2 M salt-containing buffer. Odorant-sensitive channels were directly and reversibly activated by nanomolar concentrations of the bell pepper odorant 3-isobutyl-2-methoxypyrazine and the citrus odorant 3,7,-dimethyl-2,6-octadienenitrile. These channels display burst kinetics, multiple conductance levels between 35 and 420 pS, and open times in the millisecond range. With increasing concentrations of odorant, the probability of populating the higher conductance levels increases. These results show that direct activation of channels by odorants may mediate excitation of the olfactory receptor cell.

Animals↗
PubMed1988

Structural characteristics of gap junctions. I. Channel number in coupled and uncoupled conditions.

Gap junctions between crayfish lateral axons were studied by combining anatomical and electrophysiological measurements to determine structural changes associated during uncoupling by axoplasmic acidification. In basal conditions, the junctional resistance, Rj, was approximately 60-80 k omega and the synapses appeared as two adhering membranes; 18-20-nm overall thickness, containing transverse densities (channels) spanning both membranes and the narrow extracellular gap (4-6 nm). In freeze-fracture replicas, the synapses contained greater than 3 X 10(3) gap junction plaques having a total of approximately 3.5 X 10(5) intramembrane particles. "Single" gap junction particles represented approximately 10% of the total number of gap junction particles present in the synapse. Therefore, in basal conditions, most of the gap junction particles were organized in plaques. Moreover, correlations of the total number of gap junction particles with Rj suggested that most of the junctional particles in plaques corresponded to conducting channels. Upon acidification of the axoplasm to pH 6.7-6.8, the junctional resistance increased to approximately 300 k omega and action potentials failed to propagate across the septum. Morphological measurements showed that the total number of gap junction particles in plaques decreased approximately 11-fold to 3.1 X 10(4) whereas the number of single particles dispersed in the axolemmae increased significantly. Thin sections of these synapses showed that the width of the extracellular gap increased from 4-6 nm in basal conditions to 10-20 nm under conditions where axoplasmic pH was 6.7-6.8. These observations suggest that single gap junction particles dispersed in the synapse most likely represent hemi-channels produced by the dissasembly of channels previously arranged in plaques.

Animals↗
PubMed1988

Spatial map of salts and saccharides on dog tongue.

Front and rear regions of dog tongue were tested for spatial heterogeneity with respect to monovalent chloride salts (NaCl, KCl, and NH4Cl) and sweet tastants (sucrose, D-glucose, and L-glucose) by placing them in Ussing chambers where the open-circuit potential, Voc, and short-circuit current, Isc, were measured. The responses of Voc and Isc to 0.5 M NaCl were greater in the front of the tongue than in the rear, whereas the responses of Voc and Isc to 0.5 M sucrose were greater in the rear of the tongue than in the front. These results are similar to those of published neurophysiological measurements from the chorda tympani nerve and thalamus. These data suggest that the spatial heterogeneities seen in higher taste centers are present in the isolated lingual epithelium where primary taste transduction events occur.

Ammonium Chloride↗
PubMed1988

How many channels should there be in a gap junction?

The junctional resistance of the gap junctions between the lateral giant axons of the crayfish has been measured in coupled and uncoupled conditions and the number of gap junction particles has been counted under the same conditions. From these two sets of data it can be concluded that the plaque-forming particles observed in freeze fracture replicas of the synaptic area are all gap junctional particles and that their channels are open. Based on this and published results from other isolated pairs of coupled cells, an inverse relationship has been found between the input resistance of the cells and the calculated number of open gap junctional channels between them. The relationship applies to both excitable and nonexcitable cells.

Animals↗
PubMed1987

Steric repulsion between phosphatidylcholine bilayers.

The change in pressure needed to bring egg phosphatidylcholine bilayers into contact from their equilibrium separation in excess water has been determined as a function of both distance between the bilayers and water content. A distinct upward break in the pressure-distance relation appears at an interbilayer separation of about 5 A, whereas no such deviation is present in the pressure-water content relation. Thus, this break is not a property of the dehydration process per se, but instead is attributed to steric repulsion between the mobile lipid head groups that extend 2-3 A into the fluid space between bilayers. That is, electron density profiles of these bilayers indicate that the observed break in the pressure-spacing relation occurs at a bilayer separation where extended head groups from apposing bilayers come into steric hindrance. The pressure-spacing data are used to separate steric pressure from the repulsive hydration pressure, as well as to quantitate the range and magnitude of the steric interaction. An appreciable fraction of the measured steric energy can be ascribed to a decrease in configurational entropy due to restricted head-group motion as adjacent bilayers come together.

Kinetics↗
PubMed1987

Lipid monolayer states and their relationships to bilayers.

Uncommon methods of formation and analysis of lipid monolayers have enabled the recognition of several monolayer states and the identification of that in which molecular organization corresponds closely to that of the bilayer. Monolayers were formed by continuously adding a solution of phospholipid [dimyristoyl phosphatidylcholine in hexane/ethanol, 9:1 (vol/vol)] to the air/water interface of a constant-area trough. This procedure generates unconventional surface pressure (pi)-surface concentration (gamma) isotherms, which for liquid-crystalline monolayers consist of straight lines with three prominent intersections, two of which are not apparent in conventional pi-A isotherms. The regions of linear change of pi are explicable in terms of the area dependence of alkyl chain entropy. The two breaks at lower pi delimit states in which both chains lie parallel to the surface. The third occurs at collapse, which corresponds to a true equilibrium for unstressed liposomes. Mechanical and thermodynamic properties of bilayers, particularly phase-transition parameters, correspond closely to those of monolayers with which they are in equilibrium.

Cholesterol↗
PubMed1986

Area per molecule and distribution of water in fully hydrated dilauroylphosphatidylethanolamine bilayers.

The area per lipid molecule for fully hydrated dilauroylphosphatidylethanolamine (DLPE) has been obtained in both the gel and liquid-crystalline states by combining wide-angle X-ray diffraction, electron density profiles, and previously published dilatometry results [Wilkinson, D. A., & Nagle, J. F. (1981) Biochemistry 20, 187-192]. The molecular area increases from 41.0 +/- 0.2 to 49.1 +/- 1.2 A2 upon melting from the gel to liquid-crystalline phase. The thickness of the bilayer, as measured from the electron density profiles, decreases about 4 A upon melting, from 45.2 +/- 0.3 to 41.0 +/- 0.6 A. A somewhat unexpected result is that the fluid layer between fully hydrated bilayers is the same in both gel and liquid-crystalline phases and is only about 5 A thick. From these data, plus the volume of the anhydrous DLPE molecule, it is possible to determine the number of water molecules per lipid and their approximate distribution relative to the lipid molecule. Our analysis shows that there are about 7 and 9 waters per DLPE molecule in the gel and liquid-crystalline phases, respectively. About half of the water is located in the fluid space between adjacent bilayers, and the remaining waters are intercalated into the bilayer, presumably in the head group region. There are significantly fewer water molecules in the fluid spaces between DLPE bilayers than in the fluid spaces in gel- or liquid-crystalline-phase phosphatidylcholine bilayers. This small fluid space in PE bilayers could arise from interbilayer hydrogen bond formation through the water molecules or electrostatic interactions between the amine and phosphate groups on apposing bilayers.

Gels↗
PubMed1986

Hydration force and bilayer deformation: a reevaluation.

The hydration repulsive force between lipid bilayers and the deformability of both gel and liquid-crystalline bilayers have been quantitated by an X-ray diffraction analysis of osmotically stressed liposomes. Both sampling theorem reconstructions and electron density distributions were calculated from diffraction data obtained from multilayers with applied osmotic pressures of 0-50 atm. The bilayer thickness and area per lipid molecule remain nearly constant (to within about 4%) in this pressure range, as adjacent bilayers move from their equilibrium separation in excess water to within 2-4 A of each other. This analysis indicates that the bilayers are relatively incompressible. This results differs from previously published X-ray diffraction studies of bilayer compressibility but agrees with direct mechanical measurements of the bilayer compressibility modulus. It is also found that the hydration repulsive force decays exponentially with separation between bilayers with a decay constant of 1.4 A for gel-state dipalmitoylphosphatidylcholine and 1.7 A for liquid-crystalline egg phosphatidylcholine bilayers. This implies that the exponential decay constant is not necessarily equal to the diameter of a water molecule, as has been previously suggested on experimental and theoretical grounds.

Dextrans↗
PubMed1986

One-dimensional crystals of (Na+ + K+)-ATPase dimers.

Preparations of purified (Na+ + K+)-ATPase contain both fragments of membranes and long and undulating cylindrical structures. These structures have been described as edgeways of membrane fragments. We have analyzed these structures using negative staining, thin sectioning and freeze-fracture-etch electron microscopy and describe their structure for the first time. Each cylinder is 12-19 nm in width and is comprised of an unstained core from which rows of distinct particles spaced 5-6 nm apart project on both sides. Each cylindrical structure was interpreted as a linear polymer of (alpha beta)2 dimers of (Na+ + K+)-ATPase molecules. Therefore, the particles that project from both sides are the cytoplasmic domains of the molecules of the enzyme, whereas the membrane-spanning domains form the unstained core of the cylinder. From considerations of the packing of the dimers in the cylinder we conclude that the cross-sectional area of the cytoplasmic domain should be larger than that of the membrane-spanning domain. Our results are consistent with the hypothesis that the (alpha beta) protomer is the native state of the enzyme. The (alpha beta)2 dimers observed in the fractions are the result of a secondary aggregation process occurring during the purification procedure.

Animals↗
PubMed1986

Binding of 3H-phenamil, an irreversible amiloride analog, to toad urinary bladder: effects of aldosterone and vasopressin.

Phenamil, an analog of amiloride, has previously been shown to bind specifically to sodium channels in toad bladder (J.L. Garvin et al., J. Membrane Biol. 87:45-54, 1985). In this paper, 3H-phenamil was used to measure sodium channel density in both isolated epithelial cells and intact bladders. From the specific binding to intact bladders, a channel density of 455 +/- 102 channels/micron2 was calculated. No correlation between specific binding and the magnitude of irreversible inhibition of short-circuit current was found. Pretreatment of intact bladders with 1 mg/ml trypsin reduced specific binding to isolated cells by 82 +/- 5%. In isolated cells, neither aldosterone nor vasopressin had any significant effect on specific phenamil binding. It is inferred that phenamil binds to both open and closed channels which may be either in the mucosal membrane or in the submembrane space. Finally, and rather surprisingly, we found that 3H-phenamil binds irreversibly to the basolateral membrane at concentrations as low as 4 X 10(-7) M. Therefore, care must be used in interpreting binding studies with amiloride or its analog at such concentrations.

Aldosterone↗
PubMed1986

Bretylium tosylate enhances salt taste.

Bretylium tosylate (BT), an antifibrillary drug, was found to potentiate the taste of NaCl and LiCl in both humans and rats. Application of 1 mM BT (pH 6.3) to the human tongue statistically potentiated the taste of 0.2 M NaCl and 0.2 M LiCl by 33.5% and 12.5% respectively. Electrophysiological taste responses from nucleus tractus solitarius (NTS) in rat for both hyposmotic and hyperosmotic concentrations of NaCl and 0.1 M LiCl were also increased by 30 to 40% after application of 1 mM BT. This potentiation induced by BT was reduced by amiloride in both humans and rats. Furthermore, amiloride became ineffective in inhibiting taste responses to NaCl in the presence of BT.

Adolescent↗
PubMed1986

Epithelial responses of rabbit tongues and their involvement in taste transduction.

The response of rabbit tongue, placed in a modified Ussing chamber, to salts [KCl, NaCl, NH4Cl, tetraethylammonium chloride (TEACl)], sweeteners (D-glucose, sucrose), acid (HCl), and a bitter tastant, quinine, was investigated for the first time. These experiments were conducted to further explore the new paradigm of taste transduction that correlates changes in the electrical behavior of lingual epithelia with neural responses. In addition, the responses of rabbit tongue data were compared with previously published data on dog and frog tongues. When increases in short-circuit current (Isc) for rabbit tongue induced by hyperosmotic concentrations of several salts were compared, the following sequence was found: KCl greater than NH4Cl greater than NaCl greater than TEACl. These results are consistent with previously published integrated chorda tympani responses (ICTR) as well as behavioral studies that showed that rabbits prefer KCl to NaCl with their natural diet. Pharmacological studies using ouabain and amiloride suggest that K and Na are traversing rabbit tongue through different pathways. The maximal stimulation of Isc by D-glucose and sucrose (in 50 mM NaCl) was significantly smaller than those measured for KCl and NaCl. The rabbit tongue was sensitive to HCl at concentrations less than 1 mM in agreement with ICTR measurements.

Animals↗
PubMed1985

Phenamil: an irreversible inhibitor of sodium channels in the toad urinary bladder.

Several new amiloride analogues and two reported photoaffinity analogues were tested for irreversible inhibition of short-circuit current, Isc, in toad bladder. Bromoamiloride, a photoaffinity analogue, induced 40% irreversible inhibition at 500 microM after irradiation with ultraviolet light greater than or equal to 320 nm. Iodoamiloride caused no irreversible inhibition. Of the new analogues tested, only 3,5-diamino-6-chloro-N-[(phenylamino) amino-methylene] pyrazinecarboxamide, phenamil, irreversibly inhibited Isc at concentrations of 0.05 to 5 microM when added to the mucosal solution. Irreversible inhibition of Isc by phenamil may be attributed to specific blockage of the mucosal sodium channels, which depended on: 1) time of exposure; 2) mucosal pH; 3) mucosal sodium concentration. For example, 5 microM phenamil irreversibly inhibited Isc by 38% in 103 mM Na at pH 8.6 and nearly 75% in 30 mM Na at pH 6.4 after a 40-min exposure. Irreversible inhibition occurred in two phases with time constants of less than or equal to 10 min and approximately 140 min. Due to its irreversible nature, phenamil may be used to measure channel density.

Amiloride↗
PubMed1985

Salt and acid studies on canine lingual epithelium.

A section of dog tongue just anterior to the circumvallate papillae was placed in an Ussing chamber and characterized with respect to monovalent cation transport pathways, response to HCl, and the interaction between salt and acid for the purposes of determining whether ion transport through the tongue is related to the transduction process. The primary findings of this work follow. The stimulation of the short-circuit current (Isc) with decreasing pH on the dorsal surface results from a net Cl- efflux through an amiloride- and ouabain-insensitive pathway that changed its selectivity from cationic at neutral pH to anionic at lower pH values. The stimulation is abolished at isotonic NaCl concentrations. This behavior would not be predicted from the proton-binding model to a "sour receptor" as suggested by Beidler (Handbook of Sensory Physiology; Berlin: Springer-Verlag, 1971). In symmetrical solutions of Krebs-Henseleit buffer, Isc is inhibited 30% by 10(-4) M amiloride on the mucosal side and 100% by 10(-3) M ouabain on the serosal side. These results coupled with net Cl- and Na+ flux measurements show that Isc is due to a net Cl- efflux. With 1.0 M NaCl on the dorsal side, 10(-4) M amiloride inhibits Isc 84%. In contrast, when the mucosal surface is bathed in KCl (1.0 M), CsCl (1.0 M), or HCl (10(-3) M), Isc is insensitive to both 10(-4) M amiloride and/or 10(-3) M ouabain. These data suggest that K+, Cs+, and H+ traverse the tongue through different pathways from Na+ and are not energized by a Na+ gradient.

Amiloride↗
PubMed1984

New structural model for mixed-chain phosphatidylcholine bilayers.

Multilamellar suspensions of a mixed-chain saturated phosphatidylcholine with 18 carbon atoms in the sn-1 chain and 10 carbon atoms in the sn-2 chain have been analyzed by X-ray diffraction techniques. The structural parameters for this lipid in the gel state are quite different than usual phosphatidylcholine bilayer phases. A symmetric and sharp wide-angle reflection at 4.11 A indicates that the hydrocarbon chains in hydrated C(18):C(10)PC bilayers are more tightly packed than in usual gel-state phosphatidylcholine bilayers and that there is no hydrocarbon chain tilt. The lipid thickness is about 12 A smaller than would be expected in a normal bilayer phase, and the area per molecule is 3 times the area per hydrocarbon chain. In addition, the bilayer thickness increases upon melting to the liquid-crystalline state, whereas normal bilayer phases decrease in thickness upon melting. On the basis of these data, we propose a new lipid packing model for gel-state C(18):C(10)PC bilayers in which the long C(18) chain spans the entire width of the hydrocarbon region of the bilayer and the short C(10) chain aligns or abuts with the C(10) chain from the apposing molecule. This model is novel in that there are three hydrocarbon chains per head group at the lipid-water interface. Calculations show that this phase is energetically favorable for mixed-chain lipids provided the long acyl chain is nearly twice the length of the shorter chain. In the liquid-crystalline state C(18):C(10)PC forms a normal fluid bilayer, with two chains per head group.(ABSTRACT TRUNCATED AT 250 WORDS)

Chemical Phenomena↗
PubMed1984

Interdigitated hydrocarbon chain packing causes the biphasic transition behavior in lipid/alcohol suspensions.

It has been shown recently by Rowe ((1983) Biochemistry 22, 3299-3305) that ethanol has a 'biphasic' effect on the transition temperature (Tm) of phosphatidylcholine bilayers, reducing Tm at low concentrations but increasing Tm at high concentrations. Our X-ray diffraction data show that this reversal of Tm is a consequence of the induction of an unusual gel phase, where the lipid hydrocarbon chains from apposing monolayers fully interpenetrate or interdigitate. The properties of this interdigitated phase also explain the lipid chain length dependence of the reversal in the Tm versus ethanol concentration curves and the narrow width of the transition at high ethanol concentrations, as well as spectroscopic and calorimetric data from lipid suspensions containing other drugs such as methanol, benzyl alcohol, phenyl ethanol, and chlorpromazine.

Lipid Bilayers↗
PubMed1983

Malakoplakia of testis.

Malakoplakia of the testicle was first reported in 1958. Since then approximately 25 cases have been reported. We add another case.

Aged↗