Progress in Sensory Physiology 6 PDF
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Progress in Sensory Physiology Editors: H. Autrum, D. Ottoson, E.R. Perl, R.F. Schmidt, H. Shimazu, W.D. Willis Editor-in-Chief: D. Ottoson Volume 2 1981. 103 figures. V, 187 pages ISBN 3-540-10923-4 Contents: R. Necker: Thermoreceptionand Temperature Regulation in Homeothermic Vertebrates. - G.A. Manley: A Review ofthe Auditory Physiology ofthe Reptiles. C.A. Smith: Recent Advances in Structural Correlates of Auditory Receptors. Volume 3 W.D. Willis Control of Nociceptive Transmission in the Spinal Cord 1982. 51 figures. VI, 159 pages ISBN 3-540-11510-2 Contents: Introduction: Centrifugal Control ofSensory Pathways. - BehavioralEvidence for Descending Control of NociceptiveTransmission. - Pharmacology ofAnalgesiaDueto DescendingControl Systems. - DescendingControl ofthe Flexion Reflex. - Descending Control ofSpinal Cord Nociceptive Neurons. - Correlations Betweenthe Descending Control ofSpinal Cord NociceptivePathways and the Operation ofthe Analgesia Systems. Volume 4 1983. 41 figures. V, 118 pages ISBN 3-540-12498-5 Contents: N. Mei: SensoryStructures in the Viscera. G.R. Martin: SchematicEyeModels in Vertebrates. - A. Gallego: Organization ofthe OuterPlexiform Layer ofthe TetrapodaRetina. Volume 5 1985. 83 figures. V, 174 pages ISBN 3-54O-15339-X Contents: R.C. Hardie: Functional Organization ofthe Fly Retina. - H. Machemer, J. W. Deitmer: Mechanoreception in Ciliates. - M. Lindauer, H. Martin: The BiologicalSignificance ofthe Earth's MagneticField. - H. Bleckmann: Perception of Water SurfaceWaves: How Surface Waves are Used for Prey Identification Communications. Progress in Sensory Physiology 6 Editors: H.Autrum D.Ottoson E.R.Perl R.ESchmidt H.Shimazu W.D.Willis Editor-in-Chief: D. Ottoson With Contributions by T. Sato K.B. D0ving J.A. Coles S. Mense Springer-Verlag Berlin Heidelberg NewYork Tokyo Editor-in-Chief ProfessorDr. David Ottoson Karolinska Institutet, Fysiologiska Institutionen II Solnavagen 1, 10401 Stockholm 60, Sweden Editors ProfessorDr. HansjochemAutrum Zoologisches Institut der UniversitatMunchen Luisenstrasse 14, 8000Munchen2, Germany ProfessorDr. Edward R. Perl Department ofPhysiology University ofNorth CarolinaatChapelHill ChapelHill, NC 27514, USA Professor Dr. Robert F. Schmidt Physiologisches Institut derUniversitat Rontgenring9,8700Wurzburg, Germany ProfessorDr. Hiroshi Shimazu Department ofNeurophysiology University ofTokyo, Institute ofBrainResearch 7.3.1. Hongo, Bunkyo Ku, Tokyo, Japan Professor Dr. WilliamD. Willis The MarineBiomedicalInstitute University ofTexas MedicalBranch Galveston, TX77550, USA With 86Figures and 10 Tables ISBN-13:978-3-642-70413-0 e-ISBN-13:978-3-642-70411-6 001: 10.1007/978-3-642-70411-6 Thisworkissubjecttocopyright.Allrightsarereserved,whetherthewholeorpartof thematerialisconcerned,specificaUythoseoftranslation, reprinting,re-useofillus trations,broadcasting,reproductionbyphotocopyingmachineorsimilarmeans,and storageindatabanks. Under§54oftheGermanCopyrightLaw, wherecopiesare madeforotherthanprivateuse,afeeispayableto"VerwertungsgeseUschaftWort", Munich. ©Springer-VerlagBerlinHeidelberg1986 Softcoverreprint of the hardcover 1st edition 1986 Theuseofregisterednames,trademarks,etc.inthispublicationdoesnotimply,even intheabsenceofaspecificstatement,thatsuchnamesareexemptfromtherelevant protectivelawsandregulationsandthereforefreeforgeneraluse. ProductLiability:Thepublishercangivenoguaranteeforinformationaboutdrug dosageandapplicationthereofcontainedinthisbook. Ineveryindividualcasethe respectiveusermustcheckitsaccuracybyconsultingotherpharmaceuticalliterature. Typesetting:K+VFotosatzGmbH,Beerfelden 2121/3140-543210 Contents T. Safo ReceptorPotentialinRatTasteCells 1 K.B. Drjving FunctionalPropertiesoftheFishOlfactorySystem 39 J.A. Coles Homeostasis ofExtracellular Fluid in Retinas ofInvertebratesandVertebrates 105 S. Mense Slowly Conducting Afferent Fibers from Deep Tissues: Neurobiological Properties and Central NervousActions .............................. 139 SubjectIndex 221 Receptor Potential in Rat Taste Cells T. Sato Department ofPhysiology, Nagasaki UniversitySchool ofDentistry, 7-1 Sakamoto-machi, Nagasaki 852, Japan 1 Introduction . 1 2 TasteBudCells . 2 3 RestingPotential . 4 3.1 IdentificationofTasteCell . 4 3.2 ValuesofRestingPotential . 5 4 PhysiologicalPropertiesofReceptorPotential . 6 4.1 Shape . 6 4.2 RelationwithStimulusConcentration . 8 4.3 TimeCourse . 10 5 MembraneResistance . 14 5.1 Input-ResistanceandCurrent-VoltageRelationinRestingTasteCell . 14 5.2 RelationBetweenReceptorPotentialandResistanceChange . 15 5.3 TimeCourseofResistanceChangeDuringTasteStimulation . 17 6 MechanismofGenerationofReceptorPotential . 19 7 MultipleSensitivityofTasteCell . 22 7.1 ResponseProfile . 22 7.2 RandomResponsiveness . 25 8 ContributionofDepolarizingandHyperpolarizingReceptorPotentialsto GustatoryNeuralResponse . 26 9 ActionofPotassiumBenzoate . 29 10 Summary . 34 11 References . 35 1 Introduction The physiological significance of gustatory sensation has at least three aspects: (1) the maintenance of life by ingesting nutritive substances and rejecting harmful substances; (2) the controlofsecretion ofsaliva, gastricjuice, and pan creaticjuicecontainingthe digestive enzymes and(3) the pleasures offoods and drinks in humans. 2 T. Sato Mammaliantaste cells monitor the foods and drinks comingintothe oral cavity and discriminate their chemical properties. Although most of the foods and drinks containmanydifferentkindsofmolecules, inthecaseofthephysiological experiments in the laboratory we usually restrict the number of pure chemicals representing the so-called four basic taste qualities in order to understand the fundamental mechanisms oftaste sensation. There are two different types of sensory cells, the primary and the secondary. The primary sensory cell, like an olfactory cell, has an afferent axon which extends directly from the cell body and reaches the central nervous system. On the other hand, the secondary sensory cell, like a taste cell, does not have a directlyextendedafferentaxon, butmakessynapticcontactswiththeaxonofthe first-order sensoryneuron. The restingmembranepotentialofbothsensorycells changes in response to an adequate stimulus applied to the cells, which usually initiates a slow depolarization. This is called the receptor potential or generator potential. The receptor potentialistheprecursorofthegenerationofimpulsesin thegustatorynervefiberthroughthechemicalsynapsebetweenthetastecellsand the fiber terminals. In this review, I describe the various properties ofreceptor potentialsevokedbythefourbasictastestimuliinrattastecellsasinvestigatedin our experiments with an intracellular recording technique. 2 Taste Bud Cells Thetastecells onthemammaliantonguesurfacearesituatedinthetastebudsof the lingual papillae. Thereare four types ofpapillaeonthe mammaliantongue, and the taste buds are present on the fungiform, foliate, and circumvallate papillae. The fungiform papillae in adult rats, which were used in our experi ments, are cylindrical protrusions ofthe tongue mucosa, about 0.4- 0.5 mm in height and 0.2- 0.4 mm in diameter. A single taste bud lies at the top of the fungiform papilla in the rat. The bud measures 50- 80 Ilm in the long axis and 40- 60 Ilm in the short axis (Farbman 1965). The ultrastructure of mammalian taste buds at the electron microscope level has been studied extensively with rabbit foliate papillae by Murray and his collaborators (Murray 1973). They classified the taste bud cells into four distinct types: type I (dark) cell, type II (light) cell, type III cell, and type IV (basal) cell (Murray 1969, Murray et al. 1969). Thetips ofallthecelltypes, exceptthoseofthebasalcells, reach thetaste pore. Theexistenceofthefour types oftastebudcellshas beenconfirmedinthe fungiform, foliate, and circumvallate papillae in various species of mammals (Murrayand Murray 1970, Murray 1971, Murray etal. 1972). Itwas found that thetotal numberofcellsinsingletastebudsofrabbitfoliate papillaevariesfrom 30to 80. Theshares ofthecelltypes werecalculatedtobe55070-75% for type I cells, 15%- 30% for type II cells, 5%-15% for type III cells and 1%- 5% for type IV cells (Murray 1971,1973). Murray et al. (1969) found the classical picture of afferent synaptic contacts between the type III cells and the nerve fibers in the rabbit foliate papilla taste buds, and they considered that the type III cells may be gustatory receptors. In the region ofcontact between a type III cell and an afferent nerve ending, there Receptor Potential in Rat TasteCells 3 exists an increased density of the synaptic membranes and an aggregation of empty synaptic vesicles and dark-cored vesicles in the cytoplasm adjacent to the nerve ending. These characteristics have also been found in the taste buds of fungiform and circumvallate papillae (Murray et al. 1972). Subsequently, more detailed investigations on the taste buds of rat (Fig. 1) and mouse have been carriedoutbyTakedaandhercollaborators(TakedaandHoshino1975,Takeda 1976, 1977, 1981, Takeda and Kitao 1980, Takedo et al. 1982), and they con- Fig. 1. Longitudinal sections oftaste buds from the circumvallate papilla (top) and the fungiformpapilla(bottom) intherat.EC, surroundingepithelialcells; TP, tastepore;DS, dense substance; V; pore vesicle; DG, dense granules; CV, cored vesicles; N, nerves; I, type I cells; 2, type II cells; 3, type III cells (tastecells). (Takedaand Hoshino 1975) 4 T. Sato firmedthatthetypeIIIcellsaregustatorycells. Takeda(1979), usingautoradiog raphy, found that type I, II, and III cells are all separately differentiated from the type IV (basal) cells. Furthermore, by means offluorescence histochemistry and electron microscopy, Takeda and Kitao (1980) and Takeda et al. (1982) found thatadministrationofmonoamineprecursorsleadstoanaccumulationof small dense-cored vesicles at the presynaptic membrane ofthe afferent synapse and an increase in the number and density oflarge dense-cored vesicles only in type III cells. Itis concludedthat onlythe type III cells arecapable oftaking up and storingmonoamines, which mayactas neurotransmitters from the tastecell to the afferent nerve ending. 3 Resting Potential 3.1 Identification ofTaste Cell Therestingpotentials oftastecells ofmanyanimals havebeenmeasuredwithan intracellular microelectrode, e.g. frog (Sato 1969, 1972a, Esakov and Byzov 1971, Akaike et al. 1973, 1976, Sato and Beidler 1975), mudpuppy (West and Bernard 1978), catfish (Teeter and Kare 1974), rat (Kimura and Beidler 1961, Tateda and Beidler 1964, Ozeki 1970, 1971, Ozeki and Sato 1972, Sato 1976a, Sato and Beidler 1979, 1982, 1983a,b), hamster(Kimuraand Beidler 1961), and mouse (Tonosaki and Funakoshi 1983). The mean resting potentials ofthe taste cells in these animals range from - 18 to - 40mV (Sato 1980). The resting potential of taste cells in the mammalian tongue has been measured only in fungiform papillae. Whena glass capillary microelectrodeis advanced into a taste bud cell from the surface ofthe fungiform papilla, it probably penetrates the taste cell body. The penetrationofatastecellwithinatastebudoratastedisk bya microelectrodeis signaled by a sudden appearance of both a negative resting potential and an effective membrane resistance, which can be measured with the aid of an elec trical bridge (Ozeki 1971, Ozeki and Sato 1972, Sato 1972a,b, Sato and Beidler 1975, Akaike et al. 1976, West and Bernard 1978). The microelectrode is assumed to have penetrated a taste cell according to the following criteria: (a) a changeinthe resting membrane potentialineither direction upon application of chemical stimuli; (b) a change in the cell membrane resistance during taste stimulation; (c) a return oftheslow potentialand altered resistance to the initial control level after rinsing the tongue; and (d) a disappearance of the resting potential and the membrane resistance after withdrawal of the microelectrode from the cell. The identification and penetration of a mammalian taste cell by the microelec trode seem to be more difficult than those of a frog taste cell. To record from mammalian taste cells, the microelectrode must be advanced through the taste pore a few microns in diameter; otherwise, the microelectrode will be broken easily. On the other hand, a frog taste disk 100-400 J.l.m in diameter almost coversthesummitofthefungiform papillaandcomprisesmainlythecellbodyof supporting cells in the upper layer and that of taste cells in the lower layer (Graziadei and DeHan 1971), so that a microelectrode penetrates the taste cell Receptor Potential inRatTasteCells 5 throughthesupportingcell.Theshiftinthenegativerestingpotentialuponpene tration occurs in two or three steps, which is part of the evidence of taste cell penetration in frog. However, in the case ofthe rat taste bud, cytoarchitectural studies show that the taste bud cells do not form horizontallayers composed of different cell types, but that the cells beneath a taste pore occupy the taste bud like a cluster of bananas. Therefore, the penetration by a microelectrode ofthe taste budthrough the poreusually does not result inthe appearance ofa resting potentialbytwoorthreesteps. OzekiandSato(1972)investigatedextensivelythe electrophysiology of rat taste bud cells in the fungiform papillae. The electro physiological responses of the taste bud cells to the application oftaste stimuli suggested the presence oftwo kinds ofcells. One celltype responds to chemical stimuliwithadecreaseinthemembranepotential(adepolarization), whereasthe othercelltypedoesnotrespondtostimuli. OzekiandSato(1972)consideredthat the chemically depolarized taste bud cells may be gustatory cells, and that the chemically nondepolarized cells may be other kinds of cells such as supporting cells. Sincethetype IIIcellsinthemammaliantastebudcanbeidentifiedas gustatory cells only by a careful studywith anelectronmicroscope, this celltypewas long regarded as type II (Murray 1973). A singletaste bud or disk cell can be stained iontophoreticallywith a dye-filled microelectrodethat was used first to makean intracellular recording of the cell's receptor potential (Ozeki and Oura 1972, Ozeki 1973, Sato and Beidler 1975, West and Bernard 1978); but it is very dif ficult at present to determine whether the stained cell on which the receptor potential was recorded is truly a gustatory (type III) cell. According to theelectrophysiological criteriaused byOzekiandSato(1972), we candividerattastebudcellsintotwotypes onthebasisofintracellularresponses to the four basic taste stimuli: One is a taste cellwhich responds to taste stimuli and the other is a nontaste cell which does not respond to taste stimuli. 3.2 Values ofRestingPotential Therestingpotentialofrattastecellsinfungiformpapillaewasfirstmeasuredby KimuraandBeidler(1956,1961) andsubsequentlybyTatedaandBeidler(1964). The resting potential is - 30 to - 50mV when the tongue surface is adapted to water. OzekiandSato(1972) obtainedin120rattastecellsameanrestingpoten tial of - 40mV, with a range of - 19 to - 85mV, when the tongue surfacewas adapted to 41.4roMNaC!, which is equivalentto theNaCIconcentration ofthe rat's resting saliva (Hije 1969). It is known that the magnitude of the resting potentialinatastecellisdependentontheadaptingsolution(Akaikeetal. 1976). Adapting thetongue to a lowerconcentrationofNaCI results ina higher magni tude ofresting potential. Thus, restingpotentialvalues oftastecellscanbecom paredonlyundertheconditionthatthesameadaptingsolutionisemployed. Sato and Beidler (1982) measured carefully the resting potential of rat taste cells adaptedto two differentsolutions, distilledwaterand41.4roMNaCI. Themean resting potentialwas - 36± 1mV (SE, n=78) with a range of - 20to - 60mV in41.4roMNaCIsolution, and - 50± 3mV(SE, n=22)witharange of - 20to - 70mVindistilledwater. Infrogtastecellsithasbeensuggestedthattheresting
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