Thymol-evoked Ca~(2+) mobilization and ion currents in pituitary GH_3 cells

摘要

In this study, an attempt was made to elucidate the effects of thymol, a monocyclic phenolic compound, on Ca~(2+) mobilization and ion currents in pituitary GH_3 cells with the aid of fura-2 fluorimetry and the whole-cell voltage-clamp technique. Thymol increased intracellular Ca ~(2+) concentrations ([Ca~(2+)]_i) in GH_3 cells loaded with Ca~(2+)-sensitive dye fura-2. Removing extracellular Ca~(2+) reduced the thymol-induced [Ca~(2+)]_i rise. In Ca~(2+)-free solution, thymol-evoked [Ca~(2+)]_i rise was unchanged by depleting the Ca~(2+) store with thapsigargin (1 μM), while the thapsigargin-induced [Ca~(2+)]_i rise was reduced by pretreatment with thymol. These results imply that the Ca ~(2+) stores depleted by thymol comprise thapsigargin-sensitive and thapsigargin-insensitive pools. In addition, after depletion of the internal Ca~(2+) store with 100 μM thymol in Ca~(2+)-free solution, a subsequent application of Ca~(2+) greatly induced a [Ca ~(2+)]_i increase. The results indicate that, similar to thapsigargin, 100 μM thymol may activate the capacitative calcium entry (CCE) channel. However, thymol (100 μM) had a slight depressant action in L-type calcium current (I_(CaL)). The stimulatory actions of thymol on Ca ~(2+) signaling may partly be responsible for the underlying cellular mechanisms through which it affects neuroendocrine functions.