Figure 1

Emetine decreases [Ca²⁺]_L in an intracellular store different to the ER. (A) Representative simultaneous recording of changes in both [Ca²⁺]_c (upper panel) and [Ca²⁺]_L (lower panel) in HeLa cells (2 × 10⁵ cells/ml) in the presence of 1.8 mM [Ca²⁺] ( + Ca²⁺). Black traces show the effect of first adding the combination of 10 μM ATP and 1 μM Tg followed by 50 μM emetine at the times indicated by the horizontal lines. Red traces show the [Ca²⁺] responses observed when the order of addition was reversed. (B) The upper bar graph represents the average peak [Ca²⁺]_c response (n = 5) to the combination of ATP and Tg in the absence of emetine (black bar) or in the presence of emetine (red bar). The lower bar graph (left side) shows the maximal reduction in the [Ca²⁺]_L in response to ATP and Tg in the absence of emetine (black bar) or in the presence of emetine (red bar). The right side of the bottom part displays the maximal reduction in the [Ca²⁺]_L induced by emetine before (red bar) or after application of ATP and Tg (black bar). (C) Representative traces of a typical experiment, performed as described in A) except that these were carried out in the absence of external Ca²⁺ and with 0.1 mM EGTA (-Ca²⁺). Smaller agonist-induced [Ca²⁺]_c responses were obtained than those in the presence of external Ca²⁺. (D) Bar graphs represent the average peak [Ca²⁺]_c (top) or the reduction in the [Ca²⁺]_L (bottom) elicited by ATP and Tg in presence (left red bar, n = 8) or absence (left black bar, n = 10) of emetine or those in response to emetine, before or after the addition of ATP and Tg (right side ones). Data are presented as mean ± SEM and n is the number of independent experiments. Notice that emetine decreased the ATP and Tg-induced [Ca²⁺]_c rise without having any effect on the associated [Ca²⁺]_L drop regardless of the external [Ca²⁺].