P2RX7 and interstitial cystitis: In the presence of a high extracellular concentration of ATP, which is highly related to the pathophysiological condition of interstitial cystitis (Sun et al., 2001), the P2X7 receptor can stay activated for a longer time leading to increased intracellular calcium levels (Suadicani et al., 2006) as well as increased cell permeability to larger molecules (Garcia-Marcos et al., 2006) leading to downstream signaling resulting in apoptosis and cell death (Li et al., 2014).