Pervanadate inhibits volume-sensitive chloride current in bovine chromaffin cells

The role of protein tyrosine phosphorylation in the activation of the volume-sensitive Cl- current in bovine chromaffin cells was investigated by studying the effects of inhibitors of protein tyrosine kinases (PTKs) and phosphatases (PTPs). The whole-cell current was induced by intracellular guanosine-5'-0-(3-thiotriphosphate) (GTP-[gamma-S], 100-250 microM), the nonhydrolysable GTP analogue, or by cell inflation through the patch pipette under voltage-clamp conditions. PTK inhibitors tyrphostin B46 (5-50 microM) and genistein (200 microM) did not inhibit the volume-sensitive Cl- current nor did they induce it in the absence of other stimuli. In contrast, the PTP inhibitor pervanadate (200 microM) applied intracellularly prevented activation of the current. Voltage-activated Na+ and Ca2+ currents were unaffected by pervanadate. Neither sodium orthovanadate nor hydrogen peroxide alone mimicked the action of pervanadate. Other PTP inhibitors tested, i.e. ammonium molybdate (10-100 microM), phenylarsine oxide (10 microM), and ZnCl2 (500 microM), as well as the serine/threonine protein phosphatases inhibitor okadaic acid (200 nM) failed to inhibit the volume-sensitive Cl- current. It is suggested that the inhibitory action of pervanadate indicates the involvement of protein tyrosine phosphorylation in the regulation of volume-sensitive Cl- channels in bovine chromaffin cells. The possibility of pervanadate acting via a pathway unrelated to protein phosphorylation is also discussed.