Autocrine regulation of liver cell volume by ATP release, purinergic receptor stimulation, and Cl^- channel activation

The role of ATP release in autocrine regulation of cell volume was studied in rat HTC hepatoma cells using whole-cell patch clamp techniques and a Coulter Multisizer. Exposure to hypotonie buffer caused rapid swelling to 1.338±.032 of basal volume followed by regulatory volume decrease (RVD) mediated in part by outwardlyrectified CT currents, I_Cl-Swell (-1697±121 pA at -80 mV), that showed time-dependent inactivation at depolarizing potentials. The ATP scavenger apyrase (1 U/ml) completely inhibited I_Cl-Swell and blocked RVD, consistent with a role for extracellular ATP in volume recovery. Hypotonie stress augmented ATP efflux with an increase in ATP conductance 30-fold to 16.5±10.44 pA/pF. Extracellular ATP (2.5-5 μM) but not UTP activated Cl^- currents similar to I_Cl-Swell. Putative P₂ receptor blockers suramin (100 nM) and Reactive Blue 2 (10 nM) prevented activation of I_Cl-Swell and inhibited RVD dosedependently. These observations support an important autocrine role for ATP release and purinergic receptor stimulation in regulation of membrane Cl^- permeability and liver cell volume. This work was supported by NIH Grants DK 46082 and DK 43278.