Figure 5

ER Ca²⁺ stores contribute to caspofungin-induced increases in [Ca²⁺]_i. (A) The ER Ca²⁺ stores are identified by their sensitivity to the SERCA inhibitor CPA (10 µM). Exposure to CPA led to a slow increase in [Ca²⁺]_i that returned to baseline levels while still in the presence of CPA. (B) Caffeine (30 mM) also depleted the ER Ca²⁺ stores leading to a rapid increase in [Ca²⁺]_i that soon returned to baseline levels. The subsequent application of CPA did not lead to a further rise in [Ca²⁺]_i, demonstrating that the caffeine had already depleted ER Ca²⁺ stores that are identical to CPA-sensitive Ca²⁺ stores. (C) Applying 30 mM of caffeine was enough to deplete the ER Ca²⁺ stores. The consecutive application of caspofungin while in the presence of caffeine did not change the [Ca²⁺]_i. Under these conditions, no Ca²⁺ transients were observed. (D) The [Ca²⁺]_i measured under caffeine application and subsequent caspofungin application was significantly lower than the rise in [Ca²⁺]_i measured when the ER’s Ca²⁺ stores were not depleted (the horizontal bars in the experimental recordings depict the exposure periods of defined pharmacological agents. n = number of individual investigated cells, **p < 0.01, ***p < 0.001, Mann–Whitney U test).