CHARACTERIZATION OF THE VOLTAGE-DEPENDENT PROPERTIES OF A VOLUME-SENSITIVE ANION CONDUCTANCE

Outwardly rectified, swelling-activated anion conductances have been d escribed in numerous cell types. The major functional variable observe d amongst these conductances is the extent and rate of depolarization- induced inactivation. In general, the conductances can be divided into two broad classes, those that show rapid inactivation in response to strong depolarization and those that show little or no voltage depende nce. The swelling-activated anion conductance in rat C6 glioma cells i s inactivated nearly completely by membrane depolarization above +90 m V and reactivated by membrane hyperpolarization. The kinetics of inact ivation and reactivation are fit by single and double exponentials, re spectively. Voltage-dependent behavior is well described by a simple l inear kinetic model in which the channel exists in an open or one of t hree inactivated states. pH-induced changes in voltage-dependent gatin g suggest that the voltage sensor contains critical basic amino acid r esidues. Extracellular ATP blacks the channel in a voltage-dependent m anner. The block is sensitive to the direction of net Cl- movement and increases open channel noise indicating that ATP interacts with the c hannel pore. Blockage of the channel with ATP dramatically slows depol arization-induced inactivation.