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  • Fura-2 imaging of thyrotropin-releasing hormone and dopamine effects on calcium homeostasis of bovine lactotrophs
    Akerman, S... N. ...
    Dual wavelength digital imaging microscopy to detect fura-2 has been employed to characterize in normal bovine PRL-secreting cells the effects of TRH and dopamine on the intracellular ionized calcium ... concentration Š( Ca2+Ći). Concentrations of TRH greater than 10 nM caused a rapid but transient increase in ŠCa2+Ći, arising mainly from intracellular calcium stores, since it was unaffected by lowering extracellular calcium with EGTA or blocking calcium channels with Co2+. The threshold for TRH action was close to 0.1 nM. TRH action was dose dependent, with lower concentrations (less than 1-10 nM) slowing the time to peak ŠCa2+Ći response. The TRH-induced ŠCa2+Ći rise had a Q10 of about 2. TRH caused multiple transient increases in ŠCa2+Ći, but a recovery time of 10-15 min was required for full restoration of the TRH-induced response. In some cells the ŠCa2+Ći response to TRH was polarized to one region of the cell, suggesting the following possibilities, none of them exclusive: 1) Ca2+ release sites may be localized within the cell; or 2) an efficient local mechanism exists for lowering Ca2+ once it is liberated inside the cells; or 3) barriers may exist to diffusion of Ca2+ released within the cell. Extracellular application of Co2+, Mn2+, and EGTA under basal conditions resulted in lowering of ŠCa2+Ći within seconds, consistent with tonic Ca2+ influx under resting conditions which could contribute to the basal release of hormone. Dopamine, a PRL release-inhibiting factor, also lowered ŠCa2+Ći under basal conditions. However, the ŠCa2+Ći response of lactotrophs to TRH was unaffected by dopamine. This suggests that dopamine and TRH act via separate intracellular pathways to modulate hormone secretion. Applications of forskolin preceding the TRH-induced transient rise in ŠCa2+Ći resulted in a prolonged plateau rise in ŠCa2+Ći.(trunc.)
    Vir: Endocrinology. - ISSN 0013-7227 (Let. 129, št. 1, 1991, str. 475-488)
    Vrsta gradiva - članek, sestavni del
    Leto - 1991
    Jezik - angleški
    COBISS.SI-ID - 1873369

vir: Endocrinology. - ISSN 0013-7227 (Let. 129, št. 1, 1991, str. 475-488)
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