1 1 Symposium Chemosensory Receptors Satellite DEVELOPMENT ...

61 Poster Peripheral Olfaction and Peripheral TasteEXPRESSION OF A VOLTAGE-GATED POTASSIUMCHANNEL KCNQ1 IN TASTE BUD CELLSWang H. 1 , Zhou M. 1 , Rong Q. 2 , Inoue M. 3 , Bachmanov A.A. 1 ,Margolskee R.F. 4 , Pfeifer K.E. 2 , Huang L. 1 1 Monell Chemical SensesCenter, Philadelphia, PA; 2 NICHD, NIH, Bethesda, MD; 3 TokyoUniversity of Pharmacy and Life Science, Tokyo, Japan; 4 Neuroscience,Mount Sinai School of Medicine, New York, NYBitter, sweet and umami tastes are mediated by G protein coupledreceptor T1Rs and T2Rs while sour and salty stimuli are received bychannel receptors. Activation of T1R and T2R receptors results in anelevation of cytosolic Ca 2+ in taste receptor cells. The increase in Ca 2+stimulates a non-selective monovalent cation channel TRPM5,triggering influx of cations and consequently depolarizing receptor cellmembrane potential. Interestingly, activation or inhibition of channelreceptors by salty and sour stimuli also leads to membrane potentialdepolarization. To understand how these gustatory signals ofdepolarization are converted into the release of transmitters such asATP from taste bud cells onto afferent gustatory nerves, we reason thatvoltage-gated ion channels may respond to the depolarization andregulate the output of ATP. We set out to isolate voltage-gated ionchannels using various molecular methods. Here we report theoccurrence of a voltage-gated K + channel KCNQ1 (Kv7.1) in tastepapillae. Immunohistochemistry showed that KCNQ1 is expressed in alarge number of taste bud cells in mouse circumvallate and foliatepapillae including TRPM5-expressing cells. However, in fungiformpapillae, KCNQ1 expression is in a near-total overlap with T1R3.Previous studies have shown that in fungiform, T1R3 is largelycoexpressed with T1R1, forming T1R1/T1R3 receptors for umamisubstances, suggesting that KCNQ1 may play a role in umami taste.Preliminary two-bottle tests in fact showed that KCNQ1-null youngmice exhibited reduced preferences for some umami compounds. Theresults from this study may help understand the taste perception ofpatients with long QT or Jervell and Lange-Nielsen (JLN) syndromes.62 Poster Peripheral Olfaction and Peripheral TasteCALIBRATION OF A LINGUAL ELECTRIC STIMULATOR,LATERALITY OF RESPONSE AND METALLIC TASTEMcClure S.T. 1 , Lawless H.T. 1 1 Food Science, Cornell University,Ithaca, NYMetallic tastes can arise from electrical stimulation of the tongue.Two studies compared responses to fabricated electrical stimulators (a1.5 V, anode side exposed) and to a clinical electrogustometer (RIONTR6). The first study compared responses to the battery to theelectrogustometer and found equal intensities to be at 1.61 V and 16.94db, respectively. Verbal responses showed a frequency of metallic(36%), bitter (5.3%), sour (13.6%) and other (45%) reports. A list ofover 20 responses was shown as a guide, but was not limiting. A secondstudy examined responses on three areas of the tongue on each side, tofollow up on some differences in laterality observed in the first study.Results showed no clear laterality that persists through multiple testingsessions. Responses were in no way cued (no choice suggested) in thesecond study. Frequency of reports of different qualities showedmetallic (33.1%), bitter (7.5%), sour (8.3%) and other (51%) reports.The lack of a large difference in verbal reports suggests that a list ofresponses with sufficient choices, even though some are novel, does notstrongly cue towards those novel responses. This allows for use of sucha list when procedure dictates. The lack of strong laterality overmultiple sessions supports findings by others suggesting that there is nota persistent laterality in the tongue. These results still leave open thepossibility of a less persistent laterality, changing over a time intervalshorter than the weeks tested in this study. Supported by NIH RO1-DC-06223 to HTL.63 Poster Peripheral Olfaction and Peripheral TasteAQUAPORIN EXPRESSION IN MICEWatson K.J. 1 , Gilbertson T.A. 1 1 Biology, Utah State University, Logan,UTRecent studies have begun to characterize responses to hypoosmoticstimuli in the peripheral gustatory system in mouse. Aquaporin channels(AQP) have been implicated in the initial rapid movement of waterduring this response. Cellular and behavioral responses to changes inosmolarity have been examined in 2 inbred mouse strains (C57/6ByJand 129X/SvJ) that differentially express AQP5, an apically locatedwater channel. To examine the role of AQP5 more directly, we havecharacterized behavioral responses to taste stimuli in AQP5 null mice.However, we have not observed the magnitude of differences in theseresponses we would predict based on differences in AQP5 expression inB6 and 129 mice. We are exploring the possibility that there iscompensatory expression of one or more of the other AQP channels inAQP5 null mice. As a precursor to testing this hypothesis, we havebegun identifying which additional AQP channels are present in mousetaste buds. Using RT-PCR, we have found expression of other AQPchannels including AQP2 and 3, but not AQP6 in B6 and 129 mousetaste receptor cells (TRCs). Therefore, it is plausible that expression ofthese or other AQP channels may be altered in AQP5 null mice and thatthese AQP channels may also play a role in the water transductionpathway. Studies are in progress to determine whether AQP1, 4, 7, 8and 9 are expressed in mouse and we plan to use real time qPCR andimmunocytochemistry to quantify and localize expression of AQPchannels in mouse TRCs. Supported by NIH DC007239 (KJW);DC02507 (TAG).64 Poster Peripheral Olfaction and Peripheral TasteDIETARY FAT INDUCED OBESITY ALTERS K + CHANNELEXPRESSION AND REDUCES FATTY ACIDRESPONSIVENESS IN RATSBaquero A.F. 1 , Hansen D.R. 1 , Coombs C. 1 , Gilbertson T.A. 1 1 Biology &The Center for Integrated BioSystems, Utah State University, Logan,UTRecently, using heterologous expression and patch clamp recordingto determine the fatty acid sensitivity of delayed rectifying K + (DRK)channel subtypes and quantitative real time PCR (qPCR) to measureDRK expression levels, we have shown that obesity-resistant rats (S5B)express a much higher ratio of fatty acid-sensitive (fa-s) to fatty acidinsensitive(fa-i) DRK channels (5.2:1) than those from obesity-pronerats (O-M; 1.7:1). We hypothesize that the fa-s:fa-i ratio may beimportant in peripheral fat chemosensitivity and ultimately contribute todietary fat intake. To test this idea directly, we induced obesity in anormally obesity-resistant S5B rats by placing them on a diet containing70% fat for two months. S5B rats exhibit pronounced hyperphagia anddeveloped obesity similar to that seen in obesity-prone rats on this diet.After 63 days on the high-fat diet, we analyzed expression of DRKchannels and found that the fa-s:fa-i DRK ratio dropped from 5.2:1 to0.65:1. We next recorded from taste receptor cells (TRCs) from theserats using patch clamp recording to determine if these changes inexpression correlated with reduced responsiveness to fatty acids. Onnormal diets, fatty acids (10 µM) inhibit about 90-95% of the total DRKcurrent in TRCs from S5B rats, however, after developing obesity TRCswere inhibited only ~30%. Thus the fa-s:fa-i DRK ratio is sensitive todietary fat intake and a reduced sensitivity to fatty acids in TRCs iscorrelated with higher dietary fat intake and may contribute to fatinducedobesity. Supported by DK59611 (TAG).16