标题：Caspofungin induces the release of Ca 2 ions from internal stores by activating ryanodine receptor-dependent pathways in human tracheal epithelial cells
摘要：The antimycotic drug caspofungin is known to alter the cell function of cardiomyocytes and the cilia-bearing cells of the tracheal epithelium. The objective of this study was to investigate the homeostasis of intracellular Ca2 concentration ([Ca2 ]i) after exposure to caspofungin in isolated human tracheal epithelial cells. The [Ca2 ]i was measured using the ratiometric fluoroprobe FURA-2 AM. We recorded two groups of epithelial cells with distinct responses to caspofungin exposure, which demonstrated either a rapid transient rise in [Ca2 ]i or a sustained elevation of [Ca2 ]i. Both patterns of Ca2 kinetics were still observed when an influx of transmembraneous Ca2 ions was pharmacologically inhibited. Furthermore, in extracellular buffer solutions without Ca2 ions, caspofungin exposure still evoked this characteristic rise in [Ca2 ]i. To shed light on the origin of the Ca2 ions responsible for the elevation in [Ca2 ]i we investigated the possible intracellular storage of Ca2 ions. The depletion of mitochondrial Ca2 stores using 25 µM 2,4-dinitrophenol (DNP) did not prevent the caspofungin-induced rise in [Ca2 ]i, which was rapid and transient. However, the application of caffeine (30 mM) to discharge Ca2 ions that were presumably stored in the endoplasmic reticulum (ER) prior to caspofungin exposure completely inhibited the caspofungin-induced changes in [Ca2 ]i levels. When the ER-bound IP3 receptors were blocked by 2-APB (40 µM), we observed a delayed transient rise in [Ca2 ]i as a response to the caspofungin. Inhibition of the ryanodine receptors (RyR) using 40 µM ryanodine completely prevented the caspofungin-induced elevation of [Ca2 ]i. In summary, caspofungin has been shown to trigger an increase in [Ca2 ]i independent from extracellular Ca2 ions by liberating the Ca2 ions stored in the ER, mainly via a RyR pathway.
