Fig 1. Borneol stimulated Ca²⁺ influx in HEK293 cells overexpressing TRPM8 channel.

(A-B) In the presence of 1.5 mM extracellular Ca²⁺, borneol and menthol induced an increase of cytosolic Ca²⁺ in TRPM8-expressing cells, but not in the control HEK293 cells without TRPM8 expression at 25 and 35°C. The rise of Ca²⁺ was inhibited by 10 μM AMTB, a selective TRPM8 blocker. (C) Efficacy of 100 μM borneol and menthol on inducing Ca²⁺ influx into TRPM8-expressing cells at 25 and 35°C. (D) In the absence of extracellular Ca²⁺, borneol did not change the intracellular Ca²⁺ level, while subsequent addition of extracellular Ca²⁺ resulted in robust Ca²⁺ influx. (E) Comparison between the effects of borneol and menthol at different concentrations on the induction of Ca²⁺ influx in TRPM8-expressing cells. ** P<0.01, *** P<0.001. Sample numbers are shown in the bars.