Thymol-evoked Ca 2+ Mobilization and Ion Currents in Pituitary GH 3 Cells

Abstract

In this study, an attempt was made to elucidate the effects of thymol, a monocyclic phenolic compound, on Ca²⁺ mobilization and ion currents in pituitary GH₃ cells with the aid of fura-2 fluorimetry and the whole-cell voltage-clamp technique. Thymol increased intracellular Ca²⁺ concentrations ([Ca²⁺]_i) in GH₃ cells loaded with Ca²⁺-sensitive dye fura-2. Removing extracellular Ca²⁺ reduced the thymol-induced [Ca²⁺]_i rise. In Ca²⁺-free solution, thymol-evoked [Ca²⁺]_i rise was unchanged by depleting the Ca²⁺ store with thapsigargin (1 μM), while the thapsigargin-induced [Ca²⁺]_i rise was reduced by pretreatment with thymol. These results imply that the Ca²⁺ stores depleted by thymol comprise thapsigargin-sensitive and thapsigargin-insensitive pools. In addition, after depletion of the internal Ca²⁺ store with 100 μM thymol in Ca²⁺-free solution, a subsequent application of Ca²⁺ greatly induced a [Ca²⁺]_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 Ca²⁺ signaling may partly be responsible for the underlying cellular mechanisms through which it affects neuroendocrine functions.