Figure 9

Caspofungin depletes caffeine-sensitive ER Ca²⁺ stores. (A) In the Ca²⁺-free buffer solution, exposure to caffeine (30 mM) led to a rapid and prolonged reduction in Mag-Fluo-4-fluorescence. The ER stores were replenished by a voltage-gated Ca²⁺ influx (exposure to 200 mM K⁺ ions). (B) Caffeine exposure induces the discharge of ER Ca²⁺ stores prior to caspofungin application. In addition, caspofungin did not induce a further reduction in Mag-Fluo-4-fluorescence, demonstrating that ER stores were already depleted by caffeine. (C) The addition of caffeine led to a significant reduction in the Mag-Fluo-4-fluorescence indicating that the Ca²⁺ stores in the ER were empty. Subsequent application of caspofungin in the presence of caffeine did not alter the Mag-Fluo-4-fluorescence any further. (D) Isolated mice tracheae were either exposed to caspofungin (120 µM) or kept as controls in buffer solutions. Under both conditions, we observed only minor alterations in ROS generation displayed by emission fluorescence at 590 nm. (the horizontal bars in the experimental recordings depict the exposure periods of defined pharmacological agents. n = number of individual investigated cells, ns = not significant, ***p < 0.001, two-way ANOVA).