Vasopressin Modulates Membrane Properties of Taste Cells Isolated from Bullfrogs

The effect of arginine vasopressin (AVP) on the membrane propertieswas analyzed in isolated bullfrog taste cells using a perforatedwhole-cell patch-clamp technique. AVP (100 nM) induced threekinds of responses in rod-type taste cells: appearance of inwardcurrent, inhibition of voltage ramp-induced outward currentand enhancement of the outward current. The Ca²⁺-ionophore ionomycin(3 µM) also induced inward current in taste cells. A membrane-permeablecAMP analog, 8-CPT-cAMP (0.3 mM) inhibited voltage ramp-inducedoutward current in some rod cells, but enhanced the currentin other rod cells. The results suggest that AVP may increaseeither intracellular Ca²⁺ level or cAMP level in taste cells,modulating the membrane excitability. Chem. Senses 21: 739–745,1996.     

NMDA receptors turn to another channel for inhibition

Activation of glutamate receptors generally increases neuronal excitability. However, Isaacson and Murphy show in olfactory bulb granule cells that NMDA receptor-mediated calcium influx couples to large conductance (BK) calcium-activated potassium channels. The resulting inhibition is long lasting, which may be critical to the operation of the dynamic circuitry of the bulb.     

Difference in Behavior Between Responses to Forskolin and General Odorants in Turtle Vomeronasal Organ

To elucidate the signal transduction mechanisms in the turtlevomeronasal receptor neurons, the effects of forskolin, changesin mucosal Ca²⁺ concentrations and ruthenium red on the responsesof the accessory olfactory bulb to general odorants were examined.Forskolin elicited a large response, suggesting that there arecAMP-gated channels in the vomeronasal neurons. On the otherhand, the dependence of the responses to general odorants onCa²⁺ concentrations was different from that of the responseto forskolin. A large response to an odorant (n-amyl acetate)appeared after the cAMP-mediated pathway was fully desensitizedby application of 50 µM forskolin. These results suggestthat the cAMP-mediated pathway does not contribute significantlyto generation of the response to general odorants. A concentrationof 50 µM ruthenium red significantly reduced the responsesto n-amyl acetate alone and after 50 µM forskolin desensitization,suggesting that the inositol triphosphate-mediated pathway contributespartly to generation of the responses to general odorants inthe vomeronasal neurons. Chem Senses 21: 763–771, 1996.     

Glutamate-mediated extrasynaptic inhibition: direct coupling of NMDA receptors to Ca(2+)-activated K+ channels

NMDA receptors (NMDARs) typically contribute to excitatory synaptic transmission in the CNS. While Ca(2+) influx through NMDARs plays a critical role in synaptic plasticity, direct actions of NMDAR-mediated Ca(2+) influx on neuronal excitability have not been well established. Here we show that Ca(2+) influx through NMDARs is directly coupled to activation of BK-type Ca(2+)-activated K+ channels in outside-out membrane patches from rat olfactory bulb granule cells. Repetitive stimulation of glutamatergic synapses in olfactory bulb slices evokes a slow inhibitory postsynaptic current (IPSC) in granule cells that requires both NMDARs and BK channels. The slow IPSC is enhanced by glutamate uptake blockers, suggesting that extrasynaptic NMDARs underlie the response. These findings reveal a novel inhibitory action of extrasynaptic NMDARs in the brain.     

Effects of Blue Light Pretreatments on Internode Extension Growth in Mustard Seedlings after the Transition to Darkness: Analysis of the Interaction with Phytochrome

The effects of blue light (B) pretreatments on internode extensiongrowth and their possible interaction with phytochrome mediatedresponses were examined in Sinapis alba seedlings grown for11 d under 280 µmol m^–2 s^–1 of continuousblue-deficient light from low pressure sodium lamps (SOX). SupplementaryB (16 µmol m^–2 s^–1) caused no detectable inhibitionof the first internode growth rate under continuous SOX, butgrowth rate was inhibited after transfer to darkness. This effect,and the growth promotion caused by far-red bend-of-day' lightpulses were additive. The addition of B at 16 µmol m^–2s^–1 during 11 d, or only during the first 9 or 10 d orthe latest 0.75, 1 or 2 d of the SOX pretreatment caused approximatelythe same extent of inhibition after the transition to darkness.A single hour of supplementary B before darkness caused morethan 50% of the maximum inhibition. However, 24 h of lower fluencerates of B (4 or 7 µmol m^–2 s^–1) were ineffective.Covering the internode during the supplementary B period didnot prevent the response to B after the transition to darkness.Far-red light given simultaneously with B (instead of the SOXbackground) reduced the inhibitory effect of B. Above a given threshold fluence rate, B perceived mainly inthe leaves inhibits extension growth in subsequent darkness,provided that high phytochrome photo-equilibria are presentduring the irradiation with B. Once triggered, this effect doesnot interact significantly with the ‘end-of-day’phytochrome effect. Key words: Blue light, extension growth, phytochrome     

Conductometric Method for Detecting Ion Efflux during a Single Action Potential of Chara

A simple device was developed to detect net ion efflux duringa single action potential of Chara as an increase in the electricconductance of the bathing solution. The device showed a sufficientlyhigh sensitivity and rapid response to the increase in the electricconductance. Net efflux of monovalent ions was estimated as65–660 pmol cm^–2 impluse^–1 (average 220 pmolcm^–2 impulse^–1). (Received June 28, 1985; Accepted November 13, 1985)     

Ionic Currents across the Plasmalemma of Chara inflata Cells: I. OSMOTIC EFFECTS OF SORBITOL ON K+, CI- AND LEAK CURRENTS

This paper describes experiments designed to investigate theeffects of increases in external osmotic pressure on the electrophysiologicalbehaviour of the plasmalemma in cells of the brackish-wateralga, Chara inflata. The electrical conductance of the plasmalemmaof these cells of, due to the diffusion of ions, consists mainlyof K⁺, Cl^– and leak components. The addition of sorbitolat concentrations in the range 40–280 mol m^–3 tothe external solution bathing the cells, progressively and reversiblydepolarized the cell membrane and increased the total membraneconductance, chiefly due to increases in each of the separateionic conductances. At concentrations higher than about 280mol m^–3 when the cells became plasmolysed, the effectsof sorbitol on the electrical properties of the cell ceasedto be fully reversible. When the membrane electrical potentialdifference is stepped in a negative direction with a voltage-clamp,the resulting inward current has voltage-dependent componentsconsisting of an inactivating K⁺ current, an activating Cl^–current and a constant leak current. The addition of sorbitolto the external solution modified these currents by increasingtheir magnitude, by increasing the half-time of the inactivationof the K⁺ current, and by decreasing the half-time of activationof the Cl^– current. Key words: Chara inflata, osmotic effects, K⁺ and Cl^– currents     

Influence of K-Cl cotransporter activity on activation of volume-sensitive Cl- channels in human osteoblasts

The whole cell recording mode of the patch-clamp technique was used to study the effect of hypotonic NaCl or isotonic high-KCl solution on membrane currents in a human osteoblast-like cell line, C1. Both hypotonic NaCl or isotonic high-KCl solution activated Cl^– channels expressed in these cells as described previously. The reversal potential of the induced Cl^– current is more negative when activated through hypotonic NaCl solution (–47 ± 5 mV; n = 6) compared with activation through isotonic high-KCl solution (–35 ± 3 mV; n = 8). This difference can be explained by an increase in intracellular [Cl^–] through the activity of a K-Cl cotransporter. Potassium aspartate was unable to activate the current, and furosemide or DIOA suppressed the increase in Cl^– current induced by isotonic high-KCl solution. In addition, we used the polymerase chain reaction to demonstrate the presence of KCC1–KCC4 mRNA in the osteoblast-like cell line. From these results, we conclude that human osteoblasts express functional K-Cl cotransporters in their cell membrane that seem to be able to induce the indirect activation of volume-sensitive Cl^– channels by KCl through an increase in the intracellular ion concentration followed by water influx and cell swelling. potasium-chloride cotransporter; KCC1–KCC4; chloride channels; extracellular potassium concentration buffering     

Action Potentials Evoked by Light in Traps of Dionaea muscipula Ellis

At low light intensities (less than 50 µmol m^–2s^–1) illumination evokes transient depolarization of membranepotential in mesophyll cells of the leaf-trap of Dionaea muscipulaEllis. Darkening causes hyperpolarization approximately symmetricto the response to illumination. The amplitude as well as therate of potential changes depend on light intensity. After exceedinga definite threshold (usually between 50 and 80 µmol m^–2s^–1)the depolarization plays the role of a generator potential andan all-or-none action potential (AP) is released. Switchinglight off in a depolarization phase of an AP does not changeits shape and the amplitude. When the light intensity is increasedto 80–150 µmol m^–2 s^–1 a single lightstimulus triggers two successive APs. The time interval betweenthe two APs decreases with increasing stimulus strength andreaches the minimum between 300 and 400 µmol m^–2s^–1. At higher light intensities the interval increasesagain, and finally only a single AP is triggered. It was shownthat the effect was evoked by light but not by temperature changeaccompanying illumination. An inhibitor of the photosyn-theticelectron transport chain, DCMU, blocked the generator potentialsmediating between light absorption and APs. Residual responsesto light stimuli in plants treated with DCMU had reverse polarityand strongly reduced the amplitudes. (Received September 16, 1997; Accepted January 16, 1998)     

Inward rectifier K+ channel Kir2.3 is localized at the postsynaptic membrane of excitatory synapses

Classical inwardly rectifyingK⁺ channels (Kir2.0) are responsible for maintaining theresting membrane potential near the K⁺ equilibriumpotential in various cells, including neurons. Although Kir2.3 is knownto be expressed abundantly in the forebrain, its precise localizationhas not been identified. Using an antibody specific to Kir2.3, weexamined the subcellular localization of Kir2.3 in mouse brain. Kir2.3immunoreactivity was detected in a granular pattern in restricted areasof the brain, including the olfactory bulb (OB). Immunoelectronmicroscopy of the OB revealed that Kir2.3 immunoreactivity wasspecifically clustered on the postsynaptic membrane of asymmetricsynapses between granule cells and mitral/tufted cells. Theimmunoprecipitants for Kir2.3 obtained from brain contained PSD-95 andchapsyn-110, PDZ domain-containing anchoring proteins. In vitro bindingassay further revealed that the COOH-terminal end of Kir2.3 isresponsible for the association with these anchoring proteins.Therefore, the Kir channel may be involved in formation of the restingmembrane potential of the spines and, thus, would affect the responseof N-methyl-D-aspartic acid receptor channels atthe excitatory postsynaptic membrane.

     

Changes in Outward K+ Currents in Response to Two Types of Sweeteners in Sweet Taste Transduction of Gerbil Taste Cells

Using the whole cell patch clamp technique, we measured changesin outward K⁺ currents of gerbil taste cells in response todifferent kinds of sweeteners. Outward K⁺ currents of the tastecell induced by depolarizing pulses were suppressed by sweetstimuli such as 10 mM Na-saccharin. The membrane-permeable analogof cAMP, cpt-cAMP, also decreased outward K⁺ currents. On theother hand, the K+ currents were enhanced by amino acid sweetenerssuch as 10 mM D-tryptophan. The outward K⁺ current was enhancedby external application of Ca²⁺-transporting ionophore, 5 µMionomycin, and intracellular application of 5 µM inositol-1,4,5-trisphosphate(IP₃). The outward K⁺ currents were no longer suppressed by10 mM Na-saccharin containing 20 µM gurmarin, but werestill enhanced by 10 mM D-tryptophan containing 20 µMgurmarin. These results suggest that sweet taste transductionfor one group of sweeteners such as Na-saccharin in gerbilsis concerned with an increase of the intracellular cAMP level,and that the transduction for the other group of sweetenerssuch as D-tryptophan is concerned with an increase of the intracellularIP₃ level which releases Ca²⁺ from the internal stores. Chem.Senses 22: 163–169, 1997.     

Intercellular Transport and Cytoplasmic Streaming in Chara hispida

The correlation between the velocities of cytoplasmic streamingand of translocation of ¹⁴C-photosynthate and ³²P-phosphateassociated radioactivity has been investigated in whole plantsof the green freshwater alga Chara hispida L. Tracer was suppliedto the plant's rhizoid system in a split-chamber. The velocityof cytoplasmic streaming of 52±3.3 µm s^–1compares with 57±10 µm s^–1 found for ¹⁴C-transportand 32±20 µm s^–1 found for ³²P-transport.There was no indication of intercellular translocation at avelocity faster than visible streaming. Cytochalasin B inhibitedthe translocation of ³²P and cytoplasmic streaming. CytochalasinB becomes fully effective in inhibiting streaming and transportafter an incubation time of at least 5 h. Key words: Chara hispida, Cytoplasmic streaming, Intercellular transport     

The Hydrostatic and Hydrodynamic Volumes of Polyols in Aqueous Solutions and Their Sweet Taste

The tastes and solution properties of sugar alcohols were studiedin an attempt to illuminate the mechanism of sweet taste chemoreception.The SMURF method was used to measure taste time-intensity ofaqueous solutions of sugar alcohols and the results were interpretedusing the Stevens power function and kinetic parameters. Theapparent molar volumes, apparent specific volumes, partial molarvolumes, partial specific volumes and intrinsic viscositiesof the solutions were studied. Apparent molar volume reflectsthe size of the molecule in a hydrostatic state whereas intrinsicviscosity gives a measure of the size of the molecules in ahydrodynamic state. Generally the apparent molar volumes ofthe polyols are 6–13% greater than those of the parentsugars, indicating less interaction with the water structure.Apparent specific volume values can predict taste quality, andthe average apparent specific volume for the sugar alcoholsstudied fits within the central part of the sweet range, i.e.0.5–0.68 cm³/g, which accords with their ability to elicita pure sweet taste response. Intensities and persistences ofsweetness in the polyols followed the same trend as intrinsicviscosities. Chem. Senses 22: 149–161, 1997.     

Cytoplasmic Ca2+ has No Effect on the Excitability of Chara Plasmalemma

Internodal cells of Chara australis were subjected to two consecutiveintracellular perfusions with a Ca²⁺-free EGTA medium whichdisintegrated the tonoplast within about 10 minutes and thenwith a Ca²⁺-buffered medium. All perfusion media usually contained1 mM ATP. To stop the electrogenic pump, the internode was depletedof intracellular ATP. The excitability of the plasmalemma wasnot significantly influenced by intracellular free Ca²⁺ concentrationsup to 10^–4 M. To trigger action potentials, minimum currentdensities of 1 to 2 µA cm^–2 had to be applied atall tested Ca²⁺ concentrations. In the absence of cytoplasmicATP, excitability was completely lost at all Ca²⁺ concentrations. ¹ Present address: Botanisches Institut der Universit?t Bonn,Venusbergweg 22, D-5300 Bonn, FRG. (Received September 22, 1984; Accepted March 6, 1985)     

Granule neurons in cerebellum express distinct splice variants of the inositol trisphosphate receptor that are modulated by calcium

Primary cultures of granule cells (GC) from rat cerebellar cortex were used to determine whether bioelectric activity, via a Ca²⁺/calmodulin-dependent kinase (CaMK) signaling cascade, modulates expression and exon selection in the inositol trisphosphate receptor type 1 (IP₃R1). IP₃R1 contains or lacks three exons (S1, S2, and S3) that are regulated in a regionally and temporally specific manner. The neuronal, or long, form of IP₃R1 is distinguished from peripheral tissues by inclusion of the S2 exon. Although previous studies indicated that IP₃R1 are undetectable in the cerebellar granular layer in vivo, receptor protein and mRNA are induced in cultured GC grown in medium supplemented with 25 mM KCl or NMDA, two trophic agents that promote long-term survival, compared with GC grown in 5 mM KCl. IP₃R1 induction in response to 25 mM KCl or NMDA is attenuated by coaddition of voltage-sensitive calcium channel or NMDA receptor antagonists, respectively. Actinomycin D, CaMK, and calcineurin antagonists likewise suppress induction. Unlike the major variants of IP₃R1 in Purkinje neurons, which lack S1 and S3, GC grown with trophic agents express mRNA containing these exons. Both neuronal types contain S2. Evidence obtained using mutant mice with Purkinje cell lesions, laser-microdissected GC neurons from slices, and explant cultures indicates that GC predominantly express the S1-containing variant of IP₃R1 in vivo. calmodulin; exon selection     

Electrophysiological Measurements on the Root of Atriplex hastata

The ion contents and membrane potentials of the cells of young,hydroponically cultured seedlings of Atriplex hastata L. var.salina, Wallr. have been measured at several different NaClconcentrations. The total tissue concentrations of Na⁺ and Cl^–increase as external NaCl increases, but there is always a markedexcess of internal Na⁺ over Cl^–; this is balanced by endogenousorganic anion formation with a concomitant extrusion of H⁺ tothe bathing solution. Membrane potentials of the root cells remain essentially invariantwith changes in external NaCl at approx. –130 mV; thereis no evidence of a radial gradient of potential across theroot. The potential seems to contain a cyanide-sensitive electrogeniccomponent, also invariant with NaCl concentration, of about–70 mV, and a diffusion component. The electrogenic componentseems likely to be a H⁺ efflux, probably through a H⁺ uniportATPase.     

Diurnal K+ and Anion Transport in Phaseolus Pulvinus

Diurnal movement of Phaseolus leaf is caused by deformationof the laminar pulvinus located at the joint of the leaf bladeand the petiole. The plants were cultured in solutions withvarious ion compositions, and changes of K⁺, Na⁺, Ca²⁺, Mg²⁺,Cl^–, NO₃– and P₁ concentrations both in the upperand lower parts of the laminar pulvinus were measured. Culturein 10 mM KCl solution caused an increase in K⁺ and Cl^–concentrations both in the upper and lower parts without anysignificant change in the concentration of NO₃^–; culturein 10 mM KNO₃ solution caused an increase in K⁺ and NO₃^–concentration without any significant change in the concentrationof Cl^–; and culture in 10 mM KH₂PO₄ solution caused anincrease in K⁺ and P₁ concentrations without any significantchange in the concentrations of NO₃- and Cl^–. K⁺ moved from the upper to lower parts or from the lower toupper parts diurnally in all plants cultured in any solutionmentioned above. The main inorganic anion that accompanied thisK⁺ movement was Cl^– in KCl solution, and NO₃^– inKNO₃ solution. When the seedlings were cultured in distilledwater or in KH₂PO₄ solution, neither Cl^– NO₃^– norP₁ accompanied this K⁺ movement. In these cases, mainly H⁺ and/ororganic anions are supposed to move in exchange for and/or incombination with K⁺ movement. (Received November 8, 1982; Accepted June 13, 1983)     

The Relationship between Respiration-Related Membrane Potential Slow Oscillations and Discharge Patterns in Mitral/Tufted Cells: What Are the Rules?

Background

A slow respiration-related rhythm strongly shapes the activity of the olfactory bulb. This rhythm appears as a slow oscillation that is detectable in the membrane potential, the respiration-related spike discharge of the mitral/tufted cells and the bulbar local field potential. Here, we investigated the rules that govern the manifestation of membrane potential slow oscillations (MPSOs) and respiration-related discharge activities under various afferent input conditions and cellular excitability states.

Methodology and Principal Findings

We recorded the intracellular membrane potential signals in the mitral/tufted cells of freely breathing anesthetized rats. We first demonstrated the existence of multiple types of MPSOs, which were influenced by odor stimulation and discharge activity patterns. Complementary studies using changes in the intracellular excitability state and a computational model of the mitral cell demonstrated that slow oscillations in the mitral/tufted cell membrane potential were also modulated by the intracellular excitability state, whereas the respiration-related spike activity primarily reflected the afferent input. Based on our data regarding MPSOs and spike patterns, we found that cells exhibiting an unsynchronized discharge pattern never exhibited an MPSO. In contrast, cells with a respiration-synchronized discharge pattern always exhibited an MPSO. In addition, we demonstrated that the association between spike patterns and MPSO types appeared complex.

Conclusion

We propose that both the intracellular excitability state and input strength underlie specific MPSOs, which, in turn, constrain the types of spike patterns exhibited.     

UMBONIUM VESTIARIUM (L.) (GASTROPODA, TROCHACEA) AS THE FOOD SOURCE FOR NATICID GASTROPODS AND A STARFISH ON A MALAYSIAN SANDY SHORE

Umbonium vestiarium (L.) forms virtually the entire diet of3 (possibly 4) species of naticid snails and the starfish Astropectenvappa Mueller annd Troschel on some north Penang sandy shores.Umbonium comprises about 99% of numbers and tissue of macrofauna.Predation totalled some 1.75 Umbonium (ca. 33 mg dry tissue).m^-2.day^-1 across much of the downshore sand flats rising to 2.3Umbonium (ca. 45 mg). m^-2. day^-1 near MLWS. Natica maculosaLamarck comprised > 80% of the predators and took 77–94%of the Umbonium eaten. Natica antonii Phillippi alone addedto this toll on the upper reaches of the zone while Polinicesspp and Astropecten appear to have taken 12–14% of thetotal toll of Umbonium near MLWS. Total predation is indicatedat 237–327 kJ.m^-2. year^-1 across the shore and this representsalmost the total flow of energy from primary consumers to intertidalbenthic predators on such shores and accounts for some 15.6%(lower shore)—20.5% (upper shore) of total Umbonium production. (Received 10 September 1982;