Norepinephrine is coreleased with serotonin in mouse taste buds.
ATP and serotonin (5-HT) are neurotransmitters secreted from taste bud receptor (type II) and presynaptic (type III) cells, respectively. Norepinephrine (NE) has also been proposed to be a neurotransmitter or paracrine hormone in taste buds. Yet, to date, the specific stimulus for NE release in taste buds is not well understood, and the identity of the taste cells that secrete NE is not known. Chinese hamster ovary cells were transfected with alpha(1A) adrenoceptors and loaded with fura-2 ("biosensors") to detect NE secreted from isolated mouse taste buds and taste cells. Biosensors responded to low concentrations of NE (>or=10 nm) with a reliable fura-2 signal. NE biosensors did not respond to stimulation with KCl or taste compounds. However, we recorded robust responses from NE biosensors when they were positioned against mouse circumvallate taste buds and the taste buds were stimulated with KCl (50 mm) or a mixture of taste compounds (cycloheximide, 10 microm; saccharin, 2 mm; denatonium, 1 mm; SC45647, 100 microm). NE biosensor responses evoked by stimulating taste buds were reversibly blocked by prazosin, an alpha(1A) receptor antagonist. Together, these findings indicate that taste bud cells secrete NE when they are stimulated. We isolated individual taste bud cells to identify the origin of NE release. NE was secreted only from presynaptic (type III) taste cells and not receptor (type II) cells. Stimulus-evoked NE release depended on Ca(2+) in the bathing medium. Using dual biosensors (sensitive to 5-HT and NE), we found all presynaptic cells secrete 5-HT and 33% corelease NE with 5-HT.
Huang
Yijen A
YA
Department of Physiology and Biophysics, and Program in Neuroscience, University of Miami School of Medicine, Miami, Florida 33136, USA.
Maruyama
Yutaka
Y
Roper
Stephen D
SD
D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D016466:CHO Cells; D002628:Chemoreceptor Cells / Q000187:drug effects / Q000378:metabolism*; D006224:Cricetinae; D003412:Cricetulus; D003513:Cycloheximide / Q000494:pharmacology; D016257:Fura-2; D007202:Indicators and Reagents; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D009638:Norepinephrine / Q000378:metabolism* / Q000494:pharmacology; D011189:Potassium Chloride / Q000494:pharmacology; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology; D018340:Receptors, Adrenergic, alpha-1 / Q000235:genetics; D012439:Saccharin / Q000494:pharmacology; D012701:Serotonin / Q000378:metabolism*; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology*; D013649:Taste / Q000187:drug effects / Q000502:physiology; D013650:Taste Buds / Q000187:drug effects / Q000378:metabolism*; D014059:Tongue / Q000294:innervation / Q000502:physiology*
C547714:Adra1a protein, mouse; D000317:Adrenergic alpha-Antagonists; D007202:Indicators and Reagents; D000644:Quaternary Ammonium Compounds; D018340:Receptors, Adrenergic, alpha-1; D012701:Serotonin; D011189:Potassium Chloride; D003513:Cycloheximide; D012439:Saccharin; C053525:denatonium saccharide; D016257:Fura-2; D009638:Norepinephrine