Fig. 5.

Ca²⁺ dynamics affect Zn²⁺ homeostasis in the ER. (A) Effect of thapsigargin on [Ca²⁺]_ER. Treatment with 100 nM thapsigargin, caused [Ca²⁺]_ER to decrease in the presence (n = 6 cells) and absence of (n = 6 cells) extracellular Ca²⁺. (B) Increasing [Ca²⁺]_cyto reduced [Zn²⁺]_ER. Treatment with 100 nM thapsigargin caused [Ca²⁺]_cyto (n = 5 cells) to increase; [Zn²⁺]_ER decreased (n = 6 cells) concomitantly. (C) Thapsigargin increased ER Zn²⁺ when extracellular calcium was absent. [Ca²⁺]_cyto increased (n = 4 cells) and then decreased to resting level upon treatment with 100 nM thapsigargin in calcium free Hepes-buffered Hanks Balanced Salt Solution. [Zn²⁺]_ER slightly decreased (n = 5 cells) when [Ca²⁺]_cyto increased and then increased when [Ca²⁺]_cyto returned to the resting level. (D) Increasing [Ca²⁺]_cyto by activating TrpA1 reduced [Zn²⁺]_ER. HeLa cells expressing TrpA1 were treated with AITC, causing [Ca²⁺]_cyto (n = 4 cells) to increase and [Zn²⁺]_ER (n = 4 cells) to decrease. (E) Effects of extracellular Ca²⁺ on [Zn²⁺]_ER (n = 6 cells). HeLa cells were preincubated with 100 μM ZnCl₂ for 30 min, then increasing extracellular Ca²⁺ reduced [Zn²⁺]_ER. (F) Effects of extracellular Zn²⁺ on [Ca²⁺]_ER (n = 5 cells). HeLa cells were treated with thapsigargin for 30 min to block the SERCA pump. Increasing extracellular Zn²⁺ reduced [Ca²⁺]_ER.