INVOLVEMENT OF STRETCH-ACTIVATED CL- CHANNELS IN RAMIFICATION OF MURINE MICROGLIA

A stretch-activated Cl- current (I-Cl) was investigated in cultured mu rine microglia using the whole-cell configuration of the patch-clamp t echnique. After application of membrane stretch, a Cl- current appeare d within seconds, and its amplitude increased further within 3-8 min. I-Cl underwent rundown, which was prevented by addition of 4 mM ATP to the intracellular perfusing solution. The stretch-activated Cl- curre nt exhibited outward rectification and did not show any voltage-depend ent gating. Lowering the concentration of extracellular Cl- from 142 t o 12 mM by equimolar substitution of Cl- with gluconate shifted the re versal potential of I-Cl by 41.6 +/- 1.8 mV in the depolarizing direct ion. 4,4'-Diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS) and cet amido-4'-isothiocyanatostilbene-2,2'-disulfonic acid (SITS) blocked I- Cl in a voltage- and time-dependent manner. At a test potential of +40 mV, a half-maximal blockade at 16.1 mu M DIDS and at 71.0 mu M SITS w as determined for I-Cl. At a concentration of 200 mu M, 5-nitro-2-(3-p henylpropylamino)benzoic acid or flufenamic acid blocked I-Cl by 88% a nd 75%, respectively. Each of these four Cl- channel blockers reversib ly inhibited the ramification process of microglia, whereas blockers o f voltage-gated Na+ and K+ channels did not affect the transformation of microglia from their ameboid into the ramified phenotype. It is sug gested that in microglia functional stretch-activated Cl- channels are required for the induction of ramification but not for maintaining th e ramified shape.