Protein phosphotyrosine phosphatase inhibitors suppress regulatory volume decrease and the volume-sensitive Cl- conductance in mouse fibroblasts

The effects of the protein tyrosine phosphatase (PTP) inhibitors, pervanada te, monoperoxo(picolinato)-oxo-vanadate(V) [mpV(pic)] and dephostatin, on r egulatory volume decrease (RVD) and the volume-sensitive Cl- current in mou se L-fibroblasts were studied with the aid of video microscopy and the whol e-cell patch-clamp technique. The RVD induced by the hyposmotic shift from 300 to 150 mosmol/l, was strongly suppressed in cells that had been pre-inc ubated in pervanadate (25 mu M) or in mpV(pic) (10 mu M). or subjected to e xtracellular application of dephostatin (20 mu M). The acceleration in RVD caused by gramicidin (0.5 mu M) was also slowed down by pervanadate pre-tre atment, suggesting that the PTP inhibitors affected the volume-sensitive Cl - conductance. Inhibition of the volume-sensitive Cl- current by pervanadat e (25 mu M) pre-treatment and by acutely applied dephostatin (20 mu M) was confirmed in the whole-cell experiments (by congruent to 70% and by congrue nt to 50%, respectively). Both pervanadate and dephostatin inhibited the ou tward and inward Cl- currents equally, which suggests that only the number of open channels was affected. The amplitude of the Cl- current decreased s lowly during application of dephostatin and did not recover after its termi nation. We conclude that in mouse L-fibroblasts, similar to bovine chromaff in cells, inhibition of PTPs results in the suppression of both RVD and the volume-sensitive Cl- current.