Fig 13. Mutual regulation of ATPe and Vr.

The scheme summarizes the key features of this study. In rbcs, exposure to MST7 triggers activation of two ATP permeabilities (P_ATP¹ and P_ATP²), causing [ATPe] kinetics. In the absence of P2X activation, swelling is activated by ATPe, but the magnitude of volume increase is so small that it does not trigger ATP efflux. This is shown as the arrow leading to Vr<Vr^c. Activation of a P2X receptor by ATPe leads to sodium influx, coupled to water influx and swelling. As Vr increases, it surpasses Vr^c (i.e., Vr>Vr^c), so that P_ATP is transiently activated, leading to ATP release. ATPi and ATPe denote intracellular and extracellular ATP, respectively. The chemical gradient refers to the difference between ATPi and ATPe at both sides of the plasma membrane.