title: Thyronamine induces TRPM8 channel activation in human conjunctival epithelial cells.
abstract: 3-Iodothyronamine (T1AM), an endogenous thyroid hormone (TH) metabolite, induces numerous responses including a spontaneously reversible body temperature decline. As such an effect is associated in the eye with increases in basal tear flow and thermosensitive transient receptor potential melastatin 8 (TRPM8) channel activation, we determined in human conjunctival epithelial cells (IOBA-NHC) if T1AM also acts as a cooling agent to directly affect TRPM8 activation at a constant temperature. RT-PCR and quantitative real-time PCR (qPCR) along with immunocytochemistry probed for TRPM8 gene and protein expression whereas functional activity was evaluated by comparing the effects of T1AM with those of TRPM8 mediators on intracellular Ca(2+) ([Ca(2+)]i) and whole-cell currents. TRPM8 gene and protein expression was evident and icilin (20μM), a TRPM8 agonist, increased Ca(2+) influx as well as whole-cell currents whereas BCTC (10μM), a TRPM8 antagonist, suppressed these effects. Similarly, either temperature lowering below 23°C or T1AM (1μM) induced Ca(2+) transients that were blocked by this antagonist. TRPM8 activation by both 1µM T1AM and 20μM icilin prevented capsaicin (CAP) (20μM) from inducing increases in Ca(2+) influx through TRP vanilloid 1 (TRPV1) activation, whereas BCTC did not block this response. CAP (20μM) induced a 2.5-fold increase in IL-6 release whereas during exposure to 20μM capsazepine this rise was completely blocked. Similarly, T1AM (1μM) prevented this response. Taken together, T1AM like icilin is a cooling agent since they both directly elicit TRPM8 activation at a constant temperature. Moreover, there is an inverse association between changes in TRPM8 and TRPV1 activity since these cooling agents blocked both CAP-induced TRPV1 activation and downstream rises in IL-6 release.
authors.affiliation: Charité-Universitätsmedizin Berlin, Campus Virchow-Klinikum, Klinik für Augenheilkunde, Augustenburger Platz 1, D-13353 Berlin, Germany.
authors.forename: Noushafarin
authors.initials: N
authors.lastname: Khajavi
authors.affiliation: Biological Sciences, SUNY College of Optometry, New York, NY 10036, USA; School of Ophthalmology and Optometry, Wenzhou Medical University, Wenzhou 325027, PR China.
authors.forename: Peter S
authors.initials: PS
authors.lastname: Reinach
authors.affiliation: Biological Sciences, SUNY College of Optometry, New York, NY 10036, USA.
authors.forename: Nefeli
authors.initials: N
authors.lastname: Slavi
authors.affiliation: Department of Animal Physiology and Biochemistry, Poznań University of Life Sciences, 60-637 Poznań, Poland.
authors.forename: Marek
authors.initials: M
authors.lastname: Skrzypski
authors.affiliation: Charité-Universitätsmedizin Berlin, Campus Virchow-Klinikum, Klinik für Augenheilkunde, Augustenburger Platz 1, D-13353 Berlin, Germany.
authors.forename: Alexander
authors.initials: A
authors.lastname: Lucius
authors.affiliation: Charité-Universitätsmedizin Berlin, Campus Virchow-Klinikum, Klinik für Augenheilkunde, Augustenburger Platz 1, D-13353 Berlin, Germany.
authors.forename: Olaf
authors.initials: O
authors.lastname: Strauß
authors.affiliation: Institut für Experimentelle Endokrinologie, Charité-Universitätsmedizin Berlin, Augustenburger Platz 1, D-13353 Berlin, Germany.
authors.forename: Josef
authors.initials: J
authors.lastname: Köhrle
authors.affiliation: Charité-Universitätsmedizin Berlin, Campus Virchow-Klinikum, Klinik für Augenheilkunde, Augustenburger Platz 1, D-13353 Berlin, Germany. Electronic address: stefan.mergler@charite.de.
authors.forename: Stefan
authors.initials: S
authors.lastname: Mergler
mesh_terms: D002118:Calcium / Q000378:metabolism; D002211:Capsaicin / Q000494:pharmacology; D002460:Cell Line; D003228:Conjunctiva / Q000166:cytology / Q000502:physiology; D004847:Epithelial Cells / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D006801:Humans; D015850:Interleukin-6 / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects*; D018408:Patch-Clamp Techniques; D011744:Pyrimidinones / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D050053:TRPM Cation Channels / Q000235:genetics / Q000378:metabolism*; D050916:TRPV Cation Channels / Q000378:metabolism; D013970:Thyronines / Q000494:pharmacology*
chemical_list: C487948:3-iodothyronamine; D015850:Interleukin-6; D011744:Pyrimidinones; D012333:RNA, Messenger; D050053:TRPM Cation Channels; C425966:TRPM8 protein, human; D050916:TRPV Cation Channels; C494482:TRPV1 protein, human; D013970:Thyronines; C490483:icilin; D002211:Capsaicin; D002118:Calcium
keywords: Calcium transient receptor potential melastatin 8 channel; Human conjunctival epithelium; Intracellular Ca(2+), thyronamine, interleukin (IL)-6, dry eye syndrome, planar patch-clamp technique