title: Hydrogen-deuterium exchange effects on beta-endorphin release from AtT20 murine pituitary tumor cells.
abstract: Abundant evidences demonstrate that deuterium oxide (D2O) modulates various secretory activities, but specific mechanisms remain unclear. Using AtT20 cells, we examined effects of D2O on physiological processes underlying beta-endorphin release. Immunofluorescent confocal microscopy demonstrated that 90% D2O buffer increased the amount of actin filament in cell somas and decreased it in cell processes, whereas beta-tubulin was not affected. Ca2+ imaging demonstrated that high-K+-induced Ca2+ influx was not affected during D2O treatment, but was completely inhibited upon D2O washout. The H2O/D2O replacement in internal solutions of patch electrodes reduced Ca2+ currents evoked by depolarizing voltage steps, whereas additional extracellular H2O/D2O replacement recovered the currents, suggesting that D2O gradient across plasma membrane is critical for Ca2+ channel kinetics. Radioimmunoassay of high-K+-induced beta-endorphin release demonstrated an increase during D2O treatment and a decrease upon D(2)O washout. These results demonstrate that the H2O-to-D2O-induced increase in beta-endorphin release corresponded with the redistribution of actin, and the D2O-to-H2O-induced decrease in beta-endorphin release corresponded with the inhibition of voltage-sensitive Ca2+ channels. The computer modeling suggests that the differences in the zero-point vibrational energy between protonated and deuterated amino acids produce an asymmetric distribution of these amino acids upon D2O washout and this causes the dysfunction of Ca2+ channels.
authors.affiliation: Advanced Research Institute for Science and Engineering, Waseda University, 3-4-1 Okubo Shinjuku-ku, Tokyo 169-8555, Japan.
authors.forename: Masayuki
authors.initials: M
authors.lastname: Ikeda
authors.forename: Shigeru
authors.initials: S
authors.lastname: Suzuki
authors.forename: Masahiro
authors.initials: M
authors.lastname: Kishio
authors.forename: Moritoshi
authors.initials: M
authors.lastname: Hirono
authors.forename: Takashi
authors.initials: T
authors.lastname: Sugiyama
authors.forename: Junko
authors.initials: J
authors.lastname: Matsuura
authors.forename: Teppei
authors.initials: T
authors.lastname: Suzuki
authors.forename: Takayuki
authors.initials: T
authors.lastname: Sota
authors.forename: Charles N
authors.initials: CN
authors.lastname: Allen
authors.forename: Shiro
authors.initials: S
authors.lastname: Konishi
authors.forename: Tohru
authors.initials: T
authors.lastname: Yoshioka
mesh_terms: D008841:Actin Cytoskeleton / Q000378:metabolism*; D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000187:drug effects / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects*; D045744:Cell Line, Tumor / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D003198:Computer Simulation; D017666:Deuterium Oxide / Q000494:pharmacology*; D006859:Hydrogen / Q000378:metabolism; D051379:Mice; D008954:Models, Biological; D010911:Pituitary Neoplasms / Q000378:metabolism* / Q000473:pathology; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014018:Tissue Distribution; D014867:Water / Q000378:metabolism; D001615:beta-Endorphin / Q000378:metabolism*
chemical_list: D015220:Calcium Channels; D014867:Water; D001615:beta-Endorphin; D006859:Hydrogen; D017666:Deuterium Oxide; D002118:Calcium