A VOLUME-ACTIVATED ANION CONDUCTANCE IN INSULIN-SECRETING CELLS

The whole-cell patch-clamp recording technique was used to measure vol ume-activated currents in K+-free solutions in RINm5F and HIT-T15 insu linoma cells and in dispersed rat islet cells. Cell swelling, induced by intracellular hypertonicity or extracellular hypotonicity, caused a ctivation of an outwardly rectifying conductance which could be subseq uently inactivated by hypertonic extracellular solutions. The conducta nce required adenosine 5'-triphosphate (ATP) in the pipette solution b ut was Ca2+ independent. Na+ and Cl- substitution studies suggested th at the swelling-activated current is Cl- selective with a halide perme ability sequence of Br > Cl > I. The conductance was reversibly inhibi ted by the anion channel inhibitors 4,4'-diisothiocyanatostilbene-2,2' -disulphonic acid (DIDS) and by 5-nitro-2-(3-phenylpropylamino) benzoi c acid (NPPB). Further evidence for a volume-activated anion conductan ce was provided by studies of volume regulation in insulin-secreting c ells. When RINm5F cells were exposed to a hypotonic medium, the initia l cell swelling was followed by a regulatory volume decrease (RVD). Th is RVD response was also inhibited by DIDS and by NPPB. These data the refore provide evidence for a volume-activated anion conductance in in sulin-secreting cells which could be involved in the RVD following osm otic stress. A possible role for the conductance in hypotonically indu ced insulin release is also discussed.